perlos2 - Perl under OS/2, DOS, Win0.3*, Win0.95 and WinNT.

- NAME
- SYNOPSIS
- DESCRIPTION

- Target
- Other OSes
- Prerequisites
- Starting Perl programs under OS/2 (and DOS and...)
- Starting OS/2 (and DOS) programs under Perl

- Frequently asked questions

- ``It does not work''
- I cannot run external programs
- I cannot embed perl into my program, or use perl.dll from my
- ```` and pipe-`open` do not work under DOS.
- Cannot start `find.exe "pattern" file`

- INSTALLATION

- Automatic binary installation
- Manual binary installation
- Warning

- Accessing documentation

- OS/2 .INF file
- Plain text
- Manpages
- HTML
- GNU `info` files
- PDF files
- `LaTeX` docs

- BUILD

- The short story
- Prerequisites
- Getting perl source
- Application of the patches
- Hand-editing
- Making
- Testing
- Installing the built perl
- `a.out`-style build

- Building a binary distribution
- Building custom .EXE files

- Making executables with a custom collection of statically loaded extensions
- Making executables with a custom search-paths

- Build FAQ

- Some `/` became `\` in pdksh.
- `'errno'` - unresolved external
- Problems with tr or sed
- Some problem (forget which ;-)
- Library ... not found
- Segfault in make
- op/sprintf test failure

- Specific (mis)features of OS/2 port

- `setpriority`, `getpriority`
- `system()`
- `extproc` on the first line
- Additional modules:
- Prebuilt methods:
- Prebuilt variables:
- Misfeatures
- Modifications
- Identifying DLLs
- Centralized management of resources

- Perl flavors

- perl.exe
- perl_.exe
- perl__.exe
- perl___.exe
- Why strange names?
- Why dynamic linking?
- Why chimera build?

- ENVIRONMENT

- `PERLLIB_PREFIX`
- `PERL_BADLANG`
- `PERL_BADFREE`
- `PERL_SH_DIR`
- `USE_PERL_FLOCK`
- `TMP` or `TEMP`

- Evolution

- Text-mode filehandles
- Priorities
- DLL name mangling: pre 5.6.2
- DLL name mangling: 5.6.2 and beyond
- DLL forwarder generation
- Threading
- Calls to external programs
- Memory allocation
- Threads

- BUGS
- AUTHOR
- SEE ALSO

# NAME

perlos2 - Perl under OS/2, DOS, Win0.3*, Win0.95 and WinNT.

# SYNOPSIS

One can read this document in the following formats:

            man perlos2
            view perl perlos2
            explorer perlos2.html
            info perlos2

to list some (not all may be available simultaneously), or it may be read as is: either as README.os2, or pod/perlos2.pod.

To read the .INF version of documentation (very recommended) outside of OS/2, one needs an IBM's reader (may be available on IBM ftp sites (?) (URL anyone?)) or shipped with PC DOS 7.0 and IBM's Visual Age C++ 3.5.

A copy of a Win* viewer is contained in the ``Just add OS/2 Warp'' package

      ftp://ftp.software.ibm.com/ps/products/os2/tools/jaow/jaow.zip

in ?:\JUST_ADD\view.exe. This gives one an access to EMX's .INF docs as well (text form is available in /emx/doc in EMX's distribution). There is also a different viewer named xview.

Note that if you have lynx.exe or netscape.exe installed, you can follow WWW links from this document in .INF format. If you have EMX docs installed correctly, you can follow library links (you need to have `view emxbook` working by setting `EMXBOOK` environment variable as it is described in EMX docs).

# DESCRIPTION

## Target

The target is to make OS/2 one of the best supported platform for using/building/developing Perl and Perl applications, as well as make Perl the best language to use under OS/2. The secondary target is to try to make this work under DOS and Win* as well (but not too hard).

The current state is quite close to this target. Known limitations:

- Some *nix programs use `fork()` a lot; with the mostly useful flavors of perl for OS/2 (there are several built simultaneously) this is supported; but some flavors do not support this (e.g., when Perl is called from inside REXX). Using `fork()` after useing dynamically loading extensions would not work with very old versions of EMX.

- You need a separate perl executable perl__.exe (see perl__.exe) if you want to use PM code in your application (as Perl/Tk or OpenGL Perl modules do) without having a text-mode window present.

  While using the standard perl.exe from a text-mode window is possible too, I have seen cases when this causes degradation of the system stability. Using perl__.exe avoids such a degradation.

- There is no simple way to access WPS objects. The only way I know is via `OS2::REXX` and `SOM` extensions (see the OS2::REXX manpage, Som). However, we do not have access to convenience methods of Object-REXX. (Is it possible at all? I know of no Object-REXX API.) The `SOM` extension (currently in alpha-text) may eventually remove this shortcoming; however, due to the fact that DII is not supported by the `SOM` module, using `SOM` is not as convenient as one would like it.

Please keep this list up-to-date by informing me about other items.

## Other OSes

Since OS/2 port of perl uses a remarkable EMX environment, it can run (and build extensions, and - possibly - be built itself) under any environment which can run EMX. The current list is DOS, DOS-inside-OS/2, Win0.3*, Win0.95 and WinNT. Out of many perl flavors, only one works, see perl_.exe.

Note that not all features of Perl are available under these environments. This depends on the features the extender - most probably RSX - decided to implement.

Cf. Prerequisites.

## Prerequisites

EMX

  EMX runtime is required (may be substituted by RSX). Note that it is possible to make perl_.exe to run under DOS without any external support by binding emx.exe/rsx.exe to it, see emxbind. Note that under DOS for best results one should use RSX runtime, which has much more functions working (like `fork`, `popen` and so on). In fact RSX is required if there is no VCPI present. Note the RSX requires DPMI. Many implementations of DPMI are known to be very buggy, beware!

  Only the latest runtime is supported, currently `0.9d fix 03`. Perl may run under earlier versions of EMX, but this is not tested.

  One can get different parts of EMX from, say

        http://www.leo.org/pub/comp/os/os2/leo/gnu/emx+gcc/
        http://powerusersbbs.com/pub/os2/dev/   [EMX+GCC Development]
        http://hobbes.nmsu.edu/pub/os2/dev/emx/v0.9d/

  The runtime component should have the name emxrt.zip.

  NOTE. When using emx.exe/rsx.exe, it is enough to have them on your path. One does not need to specify them explicitly (though this

        emx perl_.exe -de 0

  will work as well.)

RSX

  To run Perl on DPMI platforms one needs RSX runtime. This is needed under DOS-inside-OS/2, Win0.3*, Win0.95 and WinNT (see Other OSes). RSX would not work with VCPI only, as EMX would, it requires DMPI.

  Having RSX and the latest sh.exe one gets a fully functional *nix-ish environment under DOS, say, `fork`, ```` and pipe-`open` work. In fact, MakeMaker works (for static build), so one can have Perl development environment under DOS.

  One can get RSX from, say

        ftp://ftp.cdrom.com/pub/os2/emx09c/contrib
        ftp://ftp.uni-bielefeld.de/pub/systems/msdos/misc
        ftp://ftp.leo.org/pub/comp/os/os2/leo/devtools/emx+gcc/contrib

  Contact the author on `rainer@mathematik.uni-bielefeld.de`.

  The latest sh.exe with DOS hooks is available in

        http://www.ilyaz.org/software/os2/

  as sh_dos.zip or under similar names starting with `sh`, `pdksh` etc.

HPFS

  Perl does not care about file systems, but the perl library contains many files with long names, so to install it intact one needs a file system which supports long file names.

  Note that if you do not plan to build the perl itself, it may be possible to fool EMX to truncate file names. This is not supported, read EMX docs to see how to do it.

pdksh

  To start external programs with complicated command lines (like with pipes in between, and/or quoting of arguments), Perl uses an external shell. With EMX port such shell should be named sh.exe, and located either in the wired-in-during-compile locations (usually F:/bin), or in configurable location (see PERL_SH_DIR).

  For best results use EMX pdksh. The standard binary (5.2.14 or later) runs under DOS (with RSX) as well, see

        http://www.ilyaz.org/software/os2/

## Starting Perl programs under OS/2 (and DOS and...)

Start your Perl program foo.pl with arguments `arg1 arg2 arg3` the same way as on any other platform, by

            perl foo.pl arg1 arg2 arg3

If you want to specify perl options `-my_opts` to the perl itself (as opposed to your program), use

            perl -my_opts foo.pl arg1 arg2 arg3

Alternately, if you use OS/2-ish shell, like CMD or 4os2, put the following at the start of your perl script:

            extproc perl -S -my_opts

rename your program to foo.cmd, and start it by typing

            foo arg1 arg2 arg3

Note that because of stupid OS/2 limitations the full path of the perl script is not available when you use `extproc`, thus you are forced to use `-S` perl switch, and your script should be on the `PATH`. As a plus side, if you know a full path to your script, you may still start it with

            perl ../../blah/foo.cmd arg1 arg2 arg3

(note that the argument `-my_opts` is taken care of by the `extproc` line in your script, see `extproc` on the first line).

To understand what the above magic does, read perl docs about `-S` switch - see the perlrun manpage, and cmdref about `extproc`:

            view perl perlrun
            man perlrun
            view cmdref extproc
            help extproc

or whatever method you prefer.

There are also endless possibilities to use executable extensions of 4os2, associations of WPS and so on... However, if you use *nixish shell (like sh.exe supplied in the binary distribution), you need to follow the syntax specified in Switches in the perlrun manpage.

Note that -S switch supports scripts with additional extensions .cmd, .btm, .bat, .pl as well.

## Starting OS/2 (and DOS) programs under Perl

This is what `system()` (see system in the perlfunc manpage), ```` (see I/O Operators in the perlop manpage), and open pipe (see open in the perlfunc manpage) are for. (Avoid `exec()` (see exec in the perlfunc manpage) unless you know what you do).

Note however that to use some of these operators you need to have a sh-syntax shell installed (see Pdksh, Frequently asked questions), and perl should be able to find it (see PERL_SH_DIR).

The cases when the shell is used are:

1. One-argument `system()` (see system in the perlfunc manpage), `exec()` (see exec in the perlfunc manpage) with redirection or shell meta-characters;

2. Pipe-open (see open in the perlfunc manpage) with the command which contains redirection or shell meta-characters;

3. Backticks ```` (see I/O Operators in the perlop manpage) with the command which contains redirection or shell meta-characters;

4. If the executable called by system()/exec()/pipe-open()/```` is a script with the ``magic'' `#!` line or `extproc` line which specifies shell;

5. If the executable called by system()/exec()/pipe-open()/```` is a script without ``magic'' line, and `$ENV{EXECSHELL}` is set to shell;

6. If the executable called by system()/exec()/pipe-open()/```` is not found (is not this remark obsolete?);

7. For globbing (see glob in the perlfunc manpage, I/O Operators in the perlop manpage) (obsolete? Perl uses builtin globbing nowadays...).

For the sake of speed for a common case, in the above algorithms backslashes in the command name are not considered as shell metacharacters.

Perl starts scripts which begin with cookies `extproc` or `#!` directly, without an intervention of shell. Perl uses the same algorithm to find the executable as pdksh: if the path on `#!` line does not work, and contains `/`, then the directory part of the executable is ignored, and the executable is searched in . and on `PATH`. To find arguments for these scripts Perl uses a different algorithm than pdksh: up to 3 arguments are recognized, and trailing whitespace is stripped.

If a script does not contain such a cooky, then to avoid calling sh.exe, Perl uses the same algorithm as pdksh: if `$ENV{EXECSHELL}` is set, the script is given as the first argument to this command, if not set, then `$ENV{COMSPEC} /c` is used (or a hardwired guess if `$ENV{COMSPEC}` is not set).

When starting scripts directly, Perl uses exactly the same algorithm as for the search of script given by -S command-line option: it will look in the current directory, then on components of `$ENV{PATH}` using the following order of appended extensions: no extension, .cmd, .btm, .bat, .pl.

Note that Perl will start to look for scripts only if OS/2 cannot start the specified application, thus `system 'blah'` will not look for a script if there is an executable file blah.exe anywhere on `PATH`. In other words, `PATH` is essentially searched twice: once by the OS for an executable, then by Perl for scripts.

Note also that executable files on OS/2 can have an arbitrary extension, but .exe will be automatically appended if no dot is present in the name. The workaround is as simple as that: since blah. and blah denote the same file (at list on FAT and HPFS file systems), to start an executable residing in file n:/bin/blah (no extension) give an argument `n:/bin/blah.` (dot appended) to system().

Perl will start PM programs from VIO (=text-mode) Perl process in a separate PM session; the opposite is not true: when you start a non-PM program from a PM Perl process, Perl would not run it in a separate session. If a separate session is desired, either ensure that shell will be used, as in `system 'cmd /c myprog'`, or start it using optional arguments to `system()` documented in `OS2::Process` module. This is considered to be a feature.

# Frequently asked questions

## ``It does not work''

Perl binary distributions come with a testperl.cmd script which tries to detect common problems with misconfigured installations. There is a pretty large chance it will discover which step of the installation you managed to goof. `;-)`

## I cannot run external programs

- Did you run your programs with `-w` switch? See Starting OS/2 (and DOS) programs under Perl.

- Do you try to run internal shell commands, like ``copy a b`` (internal for cmd.exe), or ``glob a*b`` (internal for ksh)? You need to specify your shell explicitly, like ``cmd /c copy a b``, since Perl cannot deduce which commands are internal to your shell.

## I cannot embed perl into my program, or use perl.dll from my program.

Is your program EMX-compiled with `-Zmt -Zcrtdll`?

  Well, nowadays Perl DLL should be usable from a differently compiled program too... If you can run Perl code from REXX scripts (see the OS2::REXX manpage), then there are some other aspect of interaction which are overlooked by the current hackish code to support differently-compiled principal programs.

  If everything else fails, you need to build a stand-alone DLL for perl. Contact me, I did it once. Sockets would not work, as a lot of other stuff.

Did you use the ExtUtils::Embed manpage?

  Some time ago I had reports it does not work. Nowadays it is checked in the Perl test suite, so grep ./t subdirectory of the build tree (as well as *.t files in the ./lib subdirectory) to find how it should be done ``correctly''.

## ```` and pipe-`open` do not work under DOS.

This may a variant of just I cannot run external programs, or a deeper problem. Basically: you need RSX (see Prerequisites) for these commands to work, and you may need a port of sh.exe which understands command arguments. One of such ports is listed in Prerequisites under RSX. Do not forget to set variable `"PERL_SH_DIR"` as well.

DPMI is required for RSX.

## Cannot start `find.exe "pattern" file`

The whole idea of the ``standard C API to start applications'' is that the forms `foo` and `"foo"` of program arguments are completely interchangable. find breaks this paradigm;

      find "pattern" file
      find pattern file

are not equivalent; find cannot be started directly using the above API. One needs a way to surround the doublequotes in some other quoting construction, necessarily having an extra non-Unixish shell in between.

Use one of

      system 'cmd', '/c', 'find "pattern" file';
      `cmd /c 'find "pattern" file'`

This would start find.exe via cmd.exe via `sh.exe` via `perl.exe`, but this is a price to pay if you want to use non-conforming program.

# INSTALLATION

## Automatic binary installation

The most convenient way of installing a binary distribution of perl is via perl installer install.exe. Just follow the instructions, and 99% of the installation blues would go away.

Note however, that you need to have unzip.exe on your path, and EMX environment running. The latter means that if you just installed EMX, and made all the needed changes to Config.sys, you may need to reboot in between. Check EMX runtime by running

            emxrev

Binary installer also creates a folder on your desktop with some useful objects. If you need to change some aspects of the work of the binary installer, feel free to edit the file Perl.pkg. This may be useful e.g., if you need to run the installer many times and do not want to make many interactive changes in the GUI.

Things not taken care of by automatic binary installation:

`PERL_BADLANG`

  may be needed if you change your codepage after perl installation, and the new value is not supported by EMX. See PERL_BADLANG.

`PERL_BADFREE`

  see PERL_BADFREE.

Config.pm

  This file resides somewhere deep in the location you installed your perl library, find it out by

        perl -MConfig -le "print $INC{'Config.pm'}"

  While most important values in this file are updated by the binary installer, some of them may need to be hand-edited. I know no such data, please keep me informed if you find one. Moreover, manual changes to the installed version may need to be accompanied by an edit of this file.

NOTE. Because of a typo the binary installer of 5.00305 would install a variable `PERL_SHPATH` into Config.sys. Please remove this variable and put `PERL_SH_DIR` instead.

## Manual binary installation

As of version 5.00305, OS/2 perl binary distribution comes split into 11 components. Unfortunately, to enable configurable binary installation, the file paths in the zip files are not absolute, but relative to some directory.

Note that the extraction with the stored paths is still necessary (default with unzip, specify `-d` to pkunzip). However, you need to know where to extract the files. You need also to manually change entries in Config.sys to reflect where did you put the files. Note that if you have some primitive unzipper (like `pkunzip`), you may get a lot of warnings/errors during unzipping. Upgrade to `(w)unzip`.

Below is the sample of what to do to reproduce the configuration on my machine. In VIEW.EXE you can press `Ctrl-Insert` now, and cut-and-paste from the resulting file - created in the directory you started VIEW.EXE from.

For each component, we mention environment variables related to each installation directory. Either choose directories to match your values of the variables, or create/append-to variables to take into account the directories.

Perl VIO and PM executables (dynamically linked)

        unzip perl_exc.zip *.exe *.ico -d f:/emx.add/bin
        unzip perl_exc.zip *.dll -d f:/emx.add/dll

  (have the directories with `*.exe` on PATH, and `*.dll` on LIBPATH);

Perl_ VIO executable (statically linked)

        unzip perl_aou.zip -d f:/emx.add/bin

  (have the directory on PATH);

Executables for Perl utilities

        unzip perl_utl.zip -d f:/emx.add/bin

  (have the directory on PATH);

Main Perl library

        unzip perl_mlb.zip -d f:/perllib/lib

  If this directory is exactly the same as the prefix which was compiled into perl.exe, you do not need to change anything. However, for perl to find the library if you use a different path, you need to `set PERLLIB_PREFIX` in Config.sys, see PERLLIB_PREFIX.

Additional Perl modules

        unzip perl_ste.zip -d f:/perllib/lib/site_perl/5.8.8/

  Same remark as above applies. Additionally, if this directory is not one of directories on @INC (and @INC is influenced by `PERLLIB_PREFIX`), you need to put this directory and subdirectory ./os2 in `PERLLIB` or `PERL5LIB` variable. Do not use `PERL5LIB` unless you have it set already. See ENVIRONMENT in the perl manpage.

  [Check whether this extraction directory is still applicable with the new directory structure layout!]

Tools to compile Perl modules

        unzip perl_blb.zip -d f:/perllib/lib

  Same remark as for perl_ste.zip.

Manpages for Perl and utilities

        unzip perl_man.zip -d f:/perllib/man

  This directory should better be on `MANPATH`. You need to have a working man to access these files.

Manpages for Perl modules

        unzip perl_mam.zip -d f:/perllib/man

  This directory should better be on `MANPATH`. You need to have a working man to access these files.

Source for Perl documentation

        unzip perl_pod.zip -d f:/perllib/lib

  This is used by the `perldoc` program (see the perldoc manpage), and may be used to generate HTML documentation usable by WWW browsers, and documentation in zillions of other formats: `info`, `LaTeX`, `Acrobat`, `FrameMaker` and so on. [Use programs such as pod2latex etc.]

Perl manual in .INF format

        unzip perl_inf.zip -d d:/os2/book

  This directory should better be on `BOOKSHELF`.

Pdksh

        unzip perl_sh.zip -d f:/bin

  This is used by perl to run external commands which explicitly require shell, like the commands using redirection and shell metacharacters. It is also used instead of explicit /bin/sh.

  Set `PERL_SH_DIR` (see PERL_SH_DIR) if you move sh.exe from the above location.

  Note. It may be possible to use some other sh-compatible shell (untested).

After you installed the components you needed and updated the Config.sys correspondingly, you need to hand-edit Config.pm. This file resides somewhere deep in the location you installed your perl library, find it out by

      perl -MConfig -le "print $INC{'Config.pm'}"

You need to correct all the entries which look like file paths (they currently start with `f:/`).

## Warning

The automatic and manual perl installation leave precompiled paths inside perl executables. While these paths are overwriteable (see PERLLIB_PREFIX, PERL_SH_DIR), some people may prefer binary editing of paths inside the executables/DLLs.

# Accessing documentation

Depending on how you built/installed perl you may have (otherwise identical) Perl documentation in the following formats:

## OS/2 .INF file

Most probably the most convenient form. Under OS/2 view it as

      view perl
      view perl perlfunc
      view perl less
      view perl ExtUtils::MakeMaker

(currently the last two may hit a wrong location, but this may improve soon). Under Win* see SYNOPSIS.

If you want to build the docs yourself, and have OS/2 toolkit, run

            pod2ipf > perl.ipf

in /perllib/lib/pod directory, then

            ipfc /inf perl.ipf

(Expect a lot of errors during the both steps.) Now move it on your BOOKSHELF path.

## Plain text

If you have perl documentation in the source form, perl utilities installed, and GNU groff installed, you may use

            perldoc perlfunc
            perldoc less
            perldoc ExtUtils::MakeMaker

to access the perl documentation in the text form (note that you may get better results using perl manpages).

Alternately, try running pod2text on .pod files.

## Manpages

If you have man installed on your system, and you installed perl manpages, use something like this:

            man perlfunc
            man 3 less
            man ExtUtils.MakeMaker

to access documentation for different components of Perl. Start with

            man perl

Note that dot (.) is used as a package separator for documentation for packages, and as usual, sometimes you need to give the section - `3` above - to avoid shadowing by the less(1) manpage.

Make sure that the directory above the directory with manpages is on our `MANPATH`, like this

      set MANPATH=c:/man;f:/perllib/man

for Perl manpages in `f:/perllib/man/man1/` etc.

## HTML

If you have some WWW browser available, installed the Perl documentation in the source form, and Perl utilities, you can build HTML docs. Cd to directory with .pod files, and do like this

            cd f:/perllib/lib/pod
            pod2html

After this you can direct your browser the file perl.html in this directory, and go ahead with reading docs, like this:

            explore file:///f:/perllib/lib/pod/perl.html

Alternatively you may be able to get these docs prebuilt from CPAN.

## GNU `info` files

Users of Emacs would appreciate it very much, especially with `CPerl` mode loaded. You need to get latest `pod2texi` from `CPAN`, or, alternately, the prebuilt info pages.

## PDF files

for `Acrobat` are available on CPAN (may be for slightly older version of perl).

## `LaTeX` docs

can be constructed using `pod2latex`.

# BUILD

Here we discuss how to build Perl under OS/2. There is an alternative (but maybe older) view on http://www.shadow.net/~troc/os2perl.html.

## The short story

Assume that you are a seasoned porter, so are sure that all the necessary tools are already present on your system, and you know how to get the Perl source distribution. Untar it, change to the extract directory, and

      gnupatch -p0 < os2\diff.configure
      sh Configure -des -D prefix=f:/perllib
      make
      make test
      make install
      make aout_test
      make aout_install

This puts the executables in f:/perllib/bin. Manually move them to the `PATH`, manually move the built perl*.dll to `LIBPATH` (here for Perl DLL * is a not-very-meaningful hex checksum), and run

      make installcmd INSTALLCMDDIR=d:/ir/on/path

Assuming that the `man`-files were put on an appropriate location, this completes the installation of minimal Perl system. (The binary distribution contains also a lot of additional modules, and the documentation in INF format.)

What follows is a detailed guide through these steps.

## Prerequisites

You need to have the latest EMX development environment, the full GNU tool suite (gawk renamed to awk, and GNU find.exe earlier on path than the OS/2 find.exe, same with sort.exe, to check use

      find --version
      sort --version

). You need the latest version of pdksh installed as sh.exe.

Check that you have BSD libraries and headers installed, and - optionally - Berkeley DB headers and libraries, and crypt.

Possible locations to get the files:

      ftp://hobbes.nmsu.edu/os2/unix/
      ftp://ftp.cdrom.com/pub/os2/unix/
      ftp://ftp.cdrom.com/pub/os2/dev32/
      ftp://ftp.cdrom.com/pub/os2/emx09c/

It is reported that the following archives contain enough utils to build perl: gnufutil.zip, gnusutil.zip, gnututil.zip, gnused.zip, gnupatch.zip, gnuawk.zip, gnumake.zip, gnugrep.zip, bsddev.zip and ksh527rt.zip (or a later version). Note that all these utilities are known to be available from LEO:

      ftp://ftp.leo.org/pub/comp/os/os2/leo/gnu

Note also that the db.lib and db.a from the EMX distribution are not suitable for multi-threaded compile (even single-threaded flavor of Perl uses multi-threaded C RTL, for compatibility with XFree86-OS/2). Get a corrected one from

      http://www.ilyaz.org/software/os2/db_mt.zip

If you have exactly the same version of Perl installed already, make sure that no copies or perl are currently running. Later steps of the build may fail since an older version of perl.dll loaded into memory may be found. Running `make test` becomes meaningless, since the test are checking a previous build of perl (this situation is detected and reported by lib/os2_base.t test). Do not forget to unset `PERL_EMXLOAD_SEC` in environment.

Also make sure that you have /tmp directory on the current drive, and . directory in your `LIBPATH`. One may try to correct the latter condition by

      set BEGINLIBPATH .\.

if you use something like CMD.EXE or latest versions of 4os2.exe. (Setting BEGINLIBPATH to just `.` is ignored by the OS/2 kernel.)

Make sure your gcc is good for `-Zomf` linking: run `omflibs` script in /emx/lib directory.

Check that you have link386 installed. It comes standard with OS/2, but may be not installed due to customization. If typing

      link386

shows you do not have it, do Selective install, and choose `Link object modules` in Optional system utilities/More. If you get into link386 prompts, press `Ctrl-C` to exit.

## Getting perl source

You need to fetch the latest perl source (including developers releases). With some probability it is located in

      http://www.cpan.org/src/5.0
      http://www.cpan.org/src/5.0/unsupported

If not, you may need to dig in the indices to find it in the directory of the current maintainer.

Quick cycle of developers release may break the OS/2 build time to time, looking into

      http://www.cpan.org/ports/os2/

may indicate the latest release which was publicly released by the maintainer. Note that the release may include some additional patches to apply to the current source of perl.

Extract it like this

      tar vzxf perl5.00409.tar.gz

You may see a message about errors while extracting Configure. This is because there is a conflict with a similarly-named file configure.

Change to the directory of extraction.

## Application of the patches

You need to apply the patches in ./os2/diff.* like this:

      gnupatch -p0 < os2\diff.configure

You may also need to apply the patches supplied with the binary distribution of perl. It also makes sense to look on the perl5-porters mailing list for the latest OS/2-related patches (see http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/). Such patches usually contain strings `/os2/` and `patch`, so it makes sense looking for these strings.

## Hand-editing

You may look into the file ./hints/os2.sh and correct anything wrong you find there. I do not expect it is needed anywhere.

## Making

      sh Configure -des -D prefix=f:/perllib

`prefix` means: where to install the resulting perl library. Giving correct prefix you may avoid the need to specify `PERLLIB_PREFIX`, see PERLLIB_PREFIX.

Ignore the message about missing `ln`, and about `-c` option to tr. The latter is most probably already fixed, if you see it and can trace where the latter spurious warning comes from, please inform me.

Now

      make

At some moment the built may die, reporting a version mismatch or unable to run perl. This means that you do not have . in your LIBPATH, so perl.exe cannot find the needed perl67B2.dll (treat these hex digits as line noise). After this is fixed the build should finish without a lot of fuss.

## Testing

Now run

      make test

All tests should succeed (with some of them skipped). If you have the same version of Perl installed, it is crucial that you have `.` early in your LIBPATH (or in BEGINLIBPATH), otherwise your tests will most probably test the wrong version of Perl.

Some tests may generate extra messages similar to

A lot of `bad free`

  in database tests related to Berkeley DB. This should be fixed already. If it persists, you may disable this warnings, see PERL_BADFREE.

Process terminated by SIGTERM/SIGINT

  This is a standard message issued by OS/2 applications. *nix applications die in silence. It is considered to be a feature. One can easily disable this by appropriate sighandlers.

  However the test engine bleeds these message to screen in unexpected moments. Two messages of this kind should be present during testing.

To get finer test reports, call

      perl t/harness

The report with io/pipe.t failing may look like this:

      Failed Test  Status Wstat Total Fail  Failed  List of failed
      ------------------------------------------------------------
      io/pipe.t                    12    1   8.33%  9
      7 tests skipped, plus 56 subtests skipped.
      Failed 1/195 test scripts, 99.49% okay. 1/6542 subtests failed, 99.98% okay.

The reasons for most important skipped tests are:

op/fs.t

1. Checks `atime` and `mtime` of `stat()` - unfortunately, HPFS provides only 2sec time granularity (for compatibility with FAT?).

2. Checks `truncate()` on a filehandle just opened for write - I do not know why this should or should not work.

op/stat.t

  Checks `stat()`. Tests:

1. Checks `atime` and `mtime` of `stat()` - unfortunately, HPFS provides only 2sec time granularity (for compatibility with FAT?).

## Installing the built perl

If you haven't yet moved `perl*.dll` onto LIBPATH, do it now.

Run

      make install

It would put the generated files into needed locations. Manually put perl.exe, perl__.exe and perl___.exe to a location on your PATH, perl.dll to a location on your LIBPATH.

Run

      make installcmd INSTALLCMDDIR=d:/ir/on/path

to convert perl utilities to .cmd files and put them on PATH. You need to put .EXE-utilities on path manually. They are installed in `$prefix/bin`, here `$prefix` is what you gave to Configure, see Making.

If you use `man`, either move the installed */man/ directories to your `MANPATH`, or modify `MANPATH` to match the location. (One could have avoided this by providing a correct `manpath` option to ./Configure, or editing ./config.sh between configuring and making steps.)

## `a.out`-style build

Proceed as above, but make perl_.exe (see perl_.exe) by

      make perl_

test and install by

      make aout_test
      make aout_install

Manually put perl_.exe to a location on your PATH.

Note. The build process for `perl_` does not know about all the dependencies, so you should make sure that anything is up-to-date, say, by doing

      make perl_dll

first.

# Building a binary distribution

[This section provides a short overview only...]

Building should proceed differently depending on whether the version of perl you install is already present and used on your system, or is a new version not yet used. The description below assumes that the version is new, so installing its DLLs and .pm files will not disrupt the operation of your system even if some intermediate steps are not yet fully working.

The other cases require a little bit more convoluted procedures. Below I suppose that the current version of Perl is `5.8.2`, so the executables are named accordingly.

1. Fully build and test the Perl distribution. Make sure that no tests are failing with `test` and `aout_test` targets; fix the bugs in Perl and the Perl test suite detected by these tests. Make sure that `all_test` make target runs as clean as possible. Check that `os2/perlrexx.cmd` runs fine.

2. Fully install Perl, including `installcmd` target. Copy the generated DLLs to `LIBPATH`; copy the numbered Perl executables (as in perl5.8.2.exe) to `PATH`; copy `perl_.exe` to `PATH` as `perl_5.8.2.exe`. Think whether you need backward-compatibility DLLs. In most cases you do not need to install them yet; but sometime this may simplify the following steps.

3. Make sure that `CPAN.pm` can download files from CPAN. If not, you may need to manually install `Net::FTP`.

4. Install the bundle `Bundle::OS2_default`

         perl5.8.2 -MCPAN -e "install Bundle::OS2_default" < nul |& tee 00cpan_i_1

   This may take a couple of hours on 1GHz processor (when run the first time). And this should not be necessarily a smooth procedure. Some modules may not specify required dependencies, so one may need to repeat this procedure several times until the results stabilize.

         perl5.8.2 -MCPAN -e "install Bundle::OS2_default" < nul |& tee 00cpan_i_2
         perl5.8.2 -MCPAN -e "install Bundle::OS2_default" < nul |& tee 00cpan_i_3

   Even after they stabilize, some tests may fail.

   Fix as many discovered bugs as possible. Document all the bugs which are not fixed, and all the failures with unknown reasons. Inspect the produced logs 00cpan_i_1 to find suspiciously skipped tests, and other fishy events.

   Keep in mind that installation of some modules may fail too: for example, the DLLs to update may be already loaded by CPAN.pm. Inspect the `install` logs (in the example above 00cpan_i_1 etc) for errors, and install things manually, as in

         cd $CPANHOME/.cpan/build/Digest-MD5-2.31
         make install

   Some distributions may fail some tests, but you may want to install them anyway (as above, or via `force install` command of `CPAN.pm` shell-mode).

   Since this procedure may take quite a long time to complete, it makes sense to ``freeze'' your CPAN configuration by disabling periodic updates of the local copy of CPAN index: set `index_expire` to some big value (I use 365), then save the settings

         CPAN> o conf index_expire 365
         CPAN> o conf commit

   Reset back to the default value `1` when you are finished.

5. When satisfied with the results, rerun the `installcmd` target. Now you can copy `perl5.8.2.exe` to `perl.exe`, and install the other OMF-build executables: `perl__.exe` etc. They are ready to be used.

6. Change to the `./pod` directory of the build tree, download the Perl logo CamelGrayBig.BMP, and run

         ( perl2ipf > perl.ipf ) |& tee 00ipf
         ipfc /INF perl.ipf |& tee 00inf

   This produces the Perl docs online book `perl.INF`. Install in on `BOOKSHELF` path.

7. Now is the time to build statically linked executable perl_.exe which includes newly-installed via `Bundle::OS2_default` modules. Doing testing via `CPAN.pm` is going to be painfully slow, since it statically links a new executable per XS extension.

   Here is a possible workaround: create a toplevel Makefile.PL in $CPANHOME/.cpan/build/ with contents being (compare with Making executables with a custom collection of statically loaded extensions)

         use ExtUtils::MakeMaker;
         WriteMakefile NAME => 'dummy';

   execute this as

         perl_5.8.2.exe Makefile.PL <nul |& tee 00aout_c1
         make -k all test <nul |& 00aout_t1

   Again, this procedure should not be absolutely smooth. Some `Makefile.PL`'s in subdirectories may be buggy, and would not run as ``child'' scripts. The interdependency of modules can strike you; however, since non-XS modules are already installed, the prerequisites of most modules have a very good chance to be present.

   If you discover some glitches, move directories of problematic modules to a different location; if these modules are non-XS modules, you may just ignore them - they are already installed; the remaining, XS, modules you need to install manually one by one.

   After each such removal you need to rerun the `Makefile.PL`/`make` process; usually this procedure converges soon. (But be sure to convert all the necessary external C libraries from .lib format to .a format: run one of

         emxaout foo.lib
         emximp -o foo.a foo.lib

   whichever is appropriate.) Also, make sure that the DLLs for external libraries are usable with with executables compiled without `-Zmtd` options.

   When you are sure that only a few subdirectories lead to failures, you may want to add `-j4` option to `make` to speed up skipping subdirectories with already finished build.

   When you are satisfied with the results of tests, install the build C libraries for extensions:

         make install |& tee 00aout_i

   Now you can rename the file ./perl.exe generated during the last phase to perl_5.8.2.exe; place it on `PATH`; if there is an inter-dependency between some XS modules, you may need to repeat the `test`/`install` loop with this new executable and some excluded modules - until the procedure converges.

   Now you have all the necessary .a libraries for these Perl modules in the places where Perl builder can find it. Use the perl builder: change to an empty directory, create a ``dummy'' Makefile.PL again, and run

         perl_5.8.2.exe Makefile.PL |& tee 00c
         make perl                  |& tee 00p

   This should create an executable ./perl.exe with all the statically loaded extensions built in. Compare the generated perlmain.c files to make sure that during the iterations the number of loaded extensions only increases. Rename ./perl.exe to perl_5.8.2.exe on `PATH`.

   When it converges, you got a functional variant of perl_5.8.2.exe; copy it to `perl_.exe`. You are done with generation of the local Perl installation.

8. Make sure that the installed modules are actually installed in the location of the new Perl, and are not inherited from entries of @INC given for inheritance from the older versions of Perl: set `PERLLIB_582_PREFIX` to redirect the new version of Perl to a new location, and copy the installed files to this new location. Redo the tests to make sure that the versions of modules inherited from older versions of Perl are not needed.

   Actually, the log output of pod2ipf during the step 6 gives a very detailed info about which modules are loaded from which place; so you may use it as an additional verification tool.

   Check that some temporary files did not make into the perl install tree. Run something like this

         pfind . -f "!(/\.(pm|pl|ix|al|h|a|lib|txt|pod|imp|bs|dll|ld|bs|inc|xbm|yml|cgi|uu|e2x|skip|packlist|eg|cfg|html|pub|enc|all|ini|po|pot)$/i or /^\w+$/") | less

   in the install tree (both top one and sitelib one).

   Compress all the DLLs with lxlite. The tiny .exe can be compressed with `/c:max` (the bug only appears when there is a fixup in the last 6 bytes of a page (?); since the tiny executables are much smaller than a page, the bug will not hit). Do not compress `perl_.exe` - it would not work under DOS.

9. Now you can generate the binary distribution. This is done by running the test of the CPAN distribution `OS2::SoftInstaller`. Tune up the file test.pl to suit the layout of current version of Perl first. Do not forget to pack the necessary external DLLs accordingly. Include the description of the bugs and test suite failures you could not fix. Include the small-stack versions of Perl executables from Perl build directory.

   Include perl5.def so that people can relink the perl DLL preserving the binary compatibility, or can create compatibility DLLs. Include the diff files (`diff -pu old new`) of fixes you did so that people can rebuild your version. Include perl5.map so that one can use remote debugging.

10. Share what you did with the other people. Relax. Enjoy fruits of your work.

11. Brace yourself for thanks, bug reports, hate mail and spam coming as result of the previous step. No good deed should remain unpunished!

# Building custom .EXE files

The Perl executables can be easily rebuilt at any moment. Moreover, one can use the embedding interface (see the perlembed manpage) to make very customized executables.

## Making executables with a custom collection of statically loaded extensions

It is a little bit easier to do so while decreasing the list of statically loaded extensions. We discuss this case only here.

1. Change to an empty directory, and create a placeholder <Makefile.PL>:

         use ExtUtils::MakeMaker;
         WriteMakefile NAME => 'dummy';

2. Run it with the flavor of Perl (perl.exe or perl_.exe) you want to rebuild.

         perl_ Makefile.PL

3. Ask it to create new Perl executable:

         make perl

   (you may need to manually add `PERLTYPE=-DPERL_CORE` to this commandline on some versions of Perl; the symptom is that the command-line globbing does not work from OS/2 shells with the newly-compiled executable; check with

         .\perl.exe -wle "print for @ARGV" *

   ).

4. The previous step created perlmain.c which contains a list of `newXS()` calls near the end. Removing unnecessary calls, and rerunning

         make perl

   will produce a customized executable.

## Making executables with a custom search-paths

The default perl executable is flexible enough to support most usages. However, one may want something yet more flexible; for example, one may want to find Perl DLL relatively to the location of the EXE file; or one may want to ignore the environment when setting the Perl-library search patch, etc.

If you fill comfortable with embedding interface (see the perlembed manpage), such things are easy to do repeating the steps outlined in Making executables with a custom collection of statically loaded extensions, and doing more comprehensive edits to `main()` of perlmain.c. The people with little desire to understand Perl can just rename main(), and do necessary modification in a custom `main()` which calls the renamed function in appropriate time.

However, there is a third way: perl DLL exports the `main()` function and several callbacks to customize the search path. Below is a complete example of a ``Perl loader'' which

1. Looks for Perl DLL in the directory `$exedir/../dll`;

2. Prepends the above directory to `BEGINLIBPATH`;

3. Fails if the Perl DLL found via `BEGINLIBPATH` is different from what was loaded on step 1; e.g., another process could have loaded it from `LIBPATH` or from a different value of `BEGINLIBPATH`. In these cases one needs to modify the setting of the system so that this other process either does not run, or loads the DLL from `BEGINLIBPATH` with `LIBPATHSTRICT=T` (available with kernels after September 2000).

4. Loads Perl library from `$exedir/../dll/lib/`.

5. Uses Bourne shell from `$exedir/../dll/sh/ksh.exe`.

For best results compile the C file below with the same options as the Perl DLL. However, a lot of functionality will work even if the executable is not an EMX applications, e.g., if compiled with

      gcc -Wall -DDOSISH -DOS2=1 -O2 -s -Zomf -Zsys perl-starter.c -DPERL_DLL_BASENAME=\"perl312F\" -Zstack 8192 -Zlinker /PM:VIO

Here is the sample C file:

      #define INCL_DOS
      #define INCL_NOPM
      /* These are needed for compile if os2.h includes os2tk.h, not os2emx.h */
      #define INCL_DOSPROCESS
      #include <os2.h>

      #include "EXTERN.h"
      #define PERL_IN_MINIPERLMAIN_C
      #include "perl.h"

      static char *me;
      HMODULE handle;

      static void
      die_with(char *msg1, char *msg2, char *msg3, char *msg4)
      {
         ULONG c;
         char *s = " error: ";

         DosWrite(2, me, strlen(me), &c);
         DosWrite(2, s, strlen(s), &c);
         DosWrite(2, msg1, strlen(msg1), &c);
         DosWrite(2, msg2, strlen(msg2), &c);
         DosWrite(2, msg3, strlen(msg3), &c);
         DosWrite(2, msg4, strlen(msg4), &c);
         DosWrite(2, "\r\n", 2, &c);
         exit(255);
      }

      typedef ULONG (*fill_extLibpath_t)(int type, char *pre, char *post, int replace, char *msg);
      typedef int (*main_t)(int type, char *argv[], char *env[]);
      typedef int (*handler_t)(void* data, int which);

      #ifndef PERL_DLL_BASENAME
      #  define PERL_DLL_BASENAME "perl"
      #endif

      static HMODULE
      load_perl_dll(char *basename)
      {
          char buf[300], fail[260];
          STRLEN l, dirl;
          fill_extLibpath_t f;
          ULONG rc_fullname;
          HMODULE handle, handle1;

          if (_execname(buf, sizeof(buf) - 13) != 0)
              die_with("Can't find full path: ", strerror(errno), "", "");
          /* XXXX Fill `me' with new value */
          l = strlen(buf);
          while (l && buf[l-1] != '/' && buf[l-1] != '\\')
              l--;
          dirl = l - 1;
          strcpy(buf + l, basename);
          l += strlen(basename);
          strcpy(buf + l, ".dll");
          if ( (rc_fullname = DosLoadModule(fail, sizeof fail, buf, &handle)) != 0
               && DosLoadModule(fail, sizeof fail, basename, &handle) != 0 )
              die_with("Can't load DLL ", buf, "", "");
          if (rc_fullname)
              return handle;                /* was loaded with short name; all is fine */
          if (DosQueryProcAddr(handle, 0, "fill_extLibpath", (PFN*)&f))
              die_with(buf, ": DLL exports no symbol ", "fill_extLibpath", "");
          buf[dirl] = 0;
          if (f(0 /*BEGINLIBPATH*/, buf /* prepend */, NULL /* append */,
                0 /* keep old value */, me))
              die_with(me, ": prepending BEGINLIBPATH", "", "");
          if (DosLoadModule(fail, sizeof fail, basename, &handle1) != 0)
              die_with(me, ": finding perl DLL again via BEGINLIBPATH", "", "");
          buf[dirl] = '\\';
          if (handle1 != handle) {
              if (DosQueryModuleName(handle1, sizeof(fail), fail))
                  strcpy(fail, "???");
              die_with(buf, ":\n\tperl DLL via BEGINLIBPATH is different: \n\t",
                       fail,
                       "\n\tYou may need to manipulate global BEGINLIBPATH and LIBPATHSTRICT"
                       "\n\tso that the other copy is loaded via BEGINLIBPATH.");
          }
          return handle;
      }

      int
      main(int argc, char **argv, char **env)
      {
          main_t f;
          handler_t h;

          me = argv[0];
          /**/
          handle = load_perl_dll(PERL_DLL_BASENAME);

          if (DosQueryProcAddr(handle, 0, "Perl_OS2_handler_install", (PFN*)&h))
              die_with(PERL_DLL_BASENAME, ": DLL exports no symbol ", "Perl_OS2_handler_install", "");
          if ( !h((void *)"~installprefix", Perlos2_handler_perllib_from)
               || !h((void *)"~dll", Perlos2_handler_perllib_to)
               || !h((void *)"~dll/sh/ksh.exe", Perlos2_handler_perl_sh) )
              die_with(PERL_DLL_BASENAME, ": Can't install @INC manglers", "", "");

          if (DosQueryProcAddr(handle, 0, "dll_perlmain", (PFN*)&f))
              die_with(PERL_DLL_BASENAME, ": DLL exports no symbol ", "dll_perlmain", "");
          return f(argc, argv, env);
      }

# Build FAQ

## Some `/` became `\` in pdksh.

You have a very old pdksh. See Prerequisites.

## `'errno'` - unresolved external

You do not have MT-safe db.lib. See Prerequisites.

## Problems with tr or sed

reported with very old version of tr and sed.

## Some problem (forget which ;-)

You have an older version of perl.dll on your LIBPATH, which broke the build of extensions.

## Library ... not found

You did not run `omflibs`. See Prerequisites.

## Segfault in make

You use an old version of GNU make. See Prerequisites.

## op/sprintf test failure

This can result from a bug in emx sprintf which was fixed in 0.9d fix 03.

# Specific (mis)features of OS/2 port

## `setpriority`, `getpriority`

Note that these functions are compatible with *nix, not with the older ports of '94 - 95. The priorities are absolute, go from 32 to -95, lower is quicker. 0 is the default priority.

WARNING. Calling `getpriority` on a non-existing process could lock the system before Warp3 fixpak22. Starting with Warp3, Perl will use a workaround: it aborts `getpriority()` if the process is not present. This is not possible on older versions `2.*`, and has a race condition anyway.

## `system()`

Multi-argument form of `system()` allows an additional numeric argument. The meaning of this argument is described in the OS2::Process manpage.

When finding a program to run, Perl first asks the OS to look for executables on `PATH` (OS/2 adds extension .exe if no extension is present). If not found, it looks for a script with possible extensions added in this order: no extension, .cmd, .btm, .bat, .pl. If found, Perl checks the start of the file for magic strings `"#!"` and `"extproc "`. If found, Perl uses the rest of the first line as the beginning of the command line to run this script. The only mangling done to the first line is extraction of arguments (currently up to 3), and ignoring of the path-part of the ``interpreter'' name if it can't be found using the full path.

E.g., `system 'foo', 'bar', 'baz'` may lead Perl to finding C:/emx/bin/foo.cmd with the first line being

     extproc /bin/bash    -x   -c

If /bin/bash.exe is not found, then Perl looks for an executable bash.exe on `PATH`. If found in C:/emx.add/bin/bash.exe, then the above `system()` is translated to

      system qw(C:/emx.add/bin/bash.exe -x -c C:/emx/bin/foo.cmd bar baz)

One additional translation is performed: instead of /bin/sh Perl uses the hardwired-or-customized shell (see `"PERL_SH_DIR"`).

The above search for ``interpreter'' is recursive: if bash executable is not found, but bash.btm is found, Perl will investigate its first line etc. The only hardwired limit on the recursion depth is implicit: there is a limit 4 on the number of additional arguments inserted before the actual arguments given to system(). In particular, if no additional arguments are specified on the ``magic'' first lines, then the limit on the depth is 4.

If Perl finds that the found executable is of PM type when the current session is not, it will start the new process in a separate session of necessary type. Call via `OS2::Process` to disable this magic.

WARNING. Due to the described logic, you need to explicitly specify .com extension if needed. Moreover, if the executable perl5.6.1 is requested, Perl will not look for perl5.6.1.exe. [This may change in the future.]

## `extproc` on the first line

If the first chars of a Perl script are `"extproc "`, this line is treated as `#!`-line, thus all the switches on this line are processed (twice if script was started via cmd.exe). See DESCRIPTION in the perlrun manpage.

## Additional modules:

the OS2::Process manpage, the OS2::DLL manpage, the OS2::REXX manpage, the OS2::PrfDB manpage, the OS2::ExtAttr manpage. These modules provide access to additional numeric argument for `system` and to the information about the running process, to DLLs having functions with REXX signature and to the REXX runtime, to OS/2 databases in the .INI format, and to Extended Attributes.

Two additional extensions by Andreas Kaiser, `OS2::UPM`, and `OS2::FTP`, are included into `ILYAZ` directory, mirrored on CPAN. Other OS/2-related extensions are available too.

## Prebuilt methods:

`File::Copy::syscopy`

  used by `File::Copy::copy`, see the File::Copy manpage.

`DynaLoader::mod2fname`

  used by `DynaLoader` for DLL name mangling.

`Cwd::current_drive()`

  Self explanatory.

`Cwd::sys_chdir(name)`

  leaves drive as it is.

`Cwd::change_drive(name)`

  chanes the ``current'' drive.

`Cwd::sys_is_absolute(name)`

  means has drive letter and is_rooted.

`Cwd::sys_is_rooted(name)`

  means has leading `[/\\]` (maybe after a drive-letter:).

`Cwd::sys_is_relative(name)`

  means changes with current dir.

`Cwd::sys_cwd(name)`

  Interface to cwd from EMX. Used by `Cwd::cwd`.

`Cwd::sys_abspath(name, dir)`

  Really really odious function to implement. Returns absolute name of file which would have `name` if CWD were `dir`. `Dir` defaults to the current dir.

`Cwd::extLibpath([type])`

  Get current value of extended library search path. If `type` is present and positive, works with `END_LIBPATH`, if negative, works with `LIBPATHSTRICT`, otherwise with `BEGIN_LIBPATH`.

`Cwd::extLibpath_set( path [, type ] )`

  Set current value of extended library search path. If `type` is present and positive, works with <END_LIBPATH>, if negative, works with `LIBPATHSTRICT`, otherwise with `BEGIN_LIBPATH`.

`OS2::Error(do_harderror,do_exception)`

  Returns `undef` if it was not called yet, otherwise bit 1 is set if on the previous call do_harderror was enabled, bit 2 is set if on previous call do_exception was enabled.

  This function enables/disables error popups associated with hardware errors (Disk not ready etc.) and software exceptions.

  I know of no way to find out the state of popups before the first call to this function.

`OS2::Errors2Drive(drive)`

  Returns `undef` if it was not called yet, otherwise return false if errors were not requested to be written to a hard drive, or the drive letter if this was requested.

  This function may redirect error popups associated with hardware errors (Disk not ready etc.) and software exceptions to the file POPUPLOG.OS2 at the root directory of the specified drive. Overrides OS2::Error() specified by individual programs. Given argument undef will disable redirection.

  Has global effect, persists after the application exits.

  I know of no way to find out the state of redirection of popups to the disk before the first call to this function.

OS2::SysInfo()

  Returns a hash with system information. The keys of the hash are

              MAX_PATH_LENGTH, MAX_TEXT_SESSIONS, MAX_PM_SESSIONS,
              MAX_VDM_SESSIONS, BOOT_DRIVE, DYN_PRI_VARIATION,
              MAX_WAIT, MIN_SLICE, MAX_SLICE, PAGE_SIZE,
              VERSION_MAJOR, VERSION_MINOR, VERSION_REVISION,
              MS_COUNT, TIME_LOW, TIME_HIGH, TOTPHYSMEM, TOTRESMEM,
              TOTAVAILMEM, MAXPRMEM, MAXSHMEM, TIMER_INTERVAL,
              MAX_COMP_LENGTH, FOREGROUND_FS_SESSION,
              FOREGROUND_PROCESS

OS2::BootDrive()

  Returns a letter without colon.

`OS2::MorphPM(serve)`, `OS2::UnMorphPM(serve)`

  Transforms the current application into a PM application and back. The argument true means that a real message loop is going to be served. OS2::MorphPM() returns the PM message queue handle as an integer.

  See Centralized management of resources for additional details.

`OS2::Serve_Messages(force)`

  Fake on-demand retrieval of outstanding PM messages. If `force` is false, will not dispatch messages if a real message loop is known to be present. Returns number of messages retrieved.

  Dies with ``QUITing...'' if WM_QUIT message is obtained.

`OS2::Process_Messages(force [, cnt])`

  Retrieval of PM messages until window creation/destruction. If `force` is false, will not dispatch messages if a real message loop is known to be present.

  Returns change in number of windows. If `cnt` is given, it is incremented by the number of messages retrieved.

  Dies with ``QUITing...'' if WM_QUIT message is obtained.

`OS2::_control87(new,mask)`

  the same as _control87(3) of EMX. Takes integers as arguments, returns the previous coprocessor control word as an integer. Only bits in `new` which are present in `mask` are changed in the control word.

OS2::get_control87()

  gets the coprocessor control word as an integer.

`OS2::set_control87_em(new=MCW_EM,mask=MCW_EM)`

  The variant of OS2::_control87() with default values good for handling exception mask: if no `mask`, uses exception mask part of `new` only. If no `new`, disables all the floating point exceptions.

  See Misfeatures for details.

`OS2::DLLname([how [, \&xsub]])`

  Gives the information about the Perl DLL or the DLL containing the C function bound to by `&xsub`. The meaning of `how` is: default (2): full name; 0: handle; 1: module name.

(Note that some of these may be moved to different libraries - eventually).

## Prebuilt variables:

$OS2::emx_rev

  numeric value is the same as _emx_rev of EMX, a string value the same as _emx_vprt (similar to `0.9c`).

$OS2::emx_env

  same as _emx_env of EMX, a number similar to 0x8001.

$OS2::os_ver

  a number `OS_MAJOR + 0.001 * OS_MINOR`.

$OS2::is_aout

  true if the Perl library was compiled in AOUT format.

$OS2::can_fork

  true if the current executable is an AOUT EMX executable, so Perl can fork. Do not use this, use the portable check for $Config::Config{dfork}.

$OS2::nsyserror

  This variable (default is 1) controls whether to enforce the contents of $^E to start with `SYS0003`-like id. If set to 0, then the string value of $^E is what is available from the OS/2 message file. (Some messages in this file have an `SYS0003`-like id prepended, some not.)

## Misfeatures

- Since flock(3) is present in EMX, but is not functional, it is emulated by perl. To disable the emulations, set environment variable `USE_PERL_FLOCK=0`.

- Here is the list of things which may be ``broken'' on EMX (from EMX docs):

  - The functions recvmsg(3), sendmsg(3), and socketpair(3) are not implemented.

  - sock_init(3) is not required and not implemented.

  - flock(3) is not yet implemented (dummy function). (Perl has a workaround.)

  - kill(3): Special treatment of PID=0, PID=1 and PID=-1 is not implemented.

  - waitpid(3):

              WUNTRACED
                      Not implemented.
              waitpid() is not implemented for negative values of PID.

  Note that `kill -9` does not work with the current version of EMX.

- See Text-mode filehandles.

- Unix-domain sockets on OS/2 live in a pseudo-file-system `/sockets/...`. To avoid a failure to create a socket with a name of a different form, `"/socket/"` is prepended to the socket name (unless it starts with this already).

  This may lead to problems later in case the socket is accessed via the ``usual'' file-system calls using the ``initial'' name.

- Apparently, IBM used a compiler (for some period of time around '95?) which changes FP mask right and left. This is not that bad for IBM's programs, but the same compiler was used for DLLs which are used with general-purpose applications. When these DLLs are used, the state of floating-point flags in the application is not predictable.

  What is much worse, some DLLs change the floating point flags when in `_DLLInitTerm()` (e.g., TCP32IP). This means that even if you do not call any function in the DLL, just the act of loading this DLL will reset your flags. What is worse, the same compiler was used to compile some HOOK DLLs. Given that HOOK dlls are executed in the context of all the applications in the system, this means a complete unpredictablity of floating point flags on systems using such HOOK DLLs. E.g., GAMESRVR.DLL of DIVE origin changes the floating point flags on each write to the TTY of a VIO (windowed text-mode) applications.

  Some other (not completely debugged) situations when FP flags change include some video drivers (?), and some operations related to creation of the windows. People who code OpenGL may have more experience on this.

  Perl is generally used in the situation when all the floating-point exceptions are ignored, as is the default under EMX. If they are not ignored, some benign Perl programs would get a `SIGFPE` and would die a horrible death.

  To circumvent this, Perl uses two hacks. They help against one type of damage only: FP flags changed when loading a DLL.

  One of the hacks is to disable floating point exceptions on Perl startup (as is the default with EMX). This helps only with compile-time-linked DLLs changing the flags before `main()` had a chance to be called.

  The other hack is to restore FP flags after a call to dlopen(). This helps against similar damage done by DLLs `_DLLInitTerm()` at runtime. Currently no way to switch these hacks off is provided.

## Modifications

Perl modifies some standard C library calls in the following ways:

`popen`

  `my_popen` uses sh.exe if shell is required, cf. PERL_SH_DIR.

`tmpnam`

  is created using `TMP` or `TEMP` environment variable, via `tempnam`.

`tmpfile`

  If the current directory is not writable, file is created using modified `tmpnam`, so there may be a race condition.

`ctermid`

  a dummy implementation.

`stat`

  `os2_stat` special-cases /dev/tty and /dev/con.

`mkdir`, `rmdir`

  these EMX functions do not work if the path contains a trailing `/`. Perl contains a workaround for this.

`flock`

  Since flock(3) is present in EMX, but is not functional, it is emulated by perl. To disable the emulations, set environment variable `USE_PERL_FLOCK=0`.

## Identifying DLLs

All the DLLs built with the current versions of Perl have ID strings identifying the name of the extension, its version, and the version of Perl required for this DLL. Run `bldlevel DLL-name` to find this info.

## Centralized management of resources

Since to call certain OS/2 API one needs to have a correctly initialized `Win` subsystem, OS/2-specific extensions may require getting `HAB`s and `HMQ`s. If an extension would do it on its own, another extension could fail to initialize.

Perl provides a centralized management of these resources:

`HAB`

  To get the HAB, the extension should call `hab = perl_hab_GET()` in C. After this call is performed, `hab` may be accessed as `Perl_hab`. There is no need to release the HAB after it is used.

  If by some reasons perl.h cannot be included, use

        extern int Perl_hab_GET(void);

  instead.

`HMQ`

  There are two cases:

- the extension needs an `HMQ` only because some API will not work otherwise. Use `serve = 0` below.

- the extension needs an `HMQ` since it wants to engage in a PM event loop. Use `serve = 1` below.

To get an `HMQ`, the extension should call `hmq = perl_hmq_GET(serve)` in C. After this call is performed, `hmq` may be accessed as `Perl_hmq`.

To signal to Perl that HMQ is not needed any more, call `perl_hmq_UNSET(serve)`. Perl process will automatically morph/unmorph itself into/from a PM process if HMQ is needed/not-needed. Perl will automatically enable/disable `WM_QUIT` message during shutdown if the message queue is served/not-served.

NOTE. If during a shutdown there is a message queue which did not disable WM_QUIT, and which did not process the received WM_QUIT message, the shutdown will be automatically cancelled. Do not call `perl_hmq_GET(1)` unless you are going to process messages on an orderly basis.

- Treating errors reported by OS/2 API

  There are two principal conventions (it is useful to call them `Dos*` and `Win*` - though this part of the function signature is not always determined by the name of the API) of reporting the error conditions of OS/2 API. Most of `Dos*` APIs report the error code as the result of the call (so 0 means success, and there are many types of errors). Most of `Win*` API report success/fail via the result being `TRUE`/`FALSE`; to find the reason for the failure one should call `WinGetLastError()` API.

  Some `Win*` entry points also overload a ``meaningful'' return value with the error indicator; having a 0 return value indicates an error. Yet some other `Win*` entry points overload things even more, and 0 return value may mean a successful call returning a valid value 0, as well as an error condition; in the case of a 0 return value one should call `WinGetLastError()` API to distinguish a successful call from a failing one.

  By convention, all the calls to OS/2 API should indicate their failures by resetting $^E. All the Perl-accessible functions which call OS/2 API may be broken into two classes: some die()s when an API error is encountered, the other report the error via a false return value (of course, this does not concern Perl-accessible functions which expect a failure of the OS/2 API call, having some workarounds coded).

  Obviously, in the situation of the last type of the signature of an OS/2 API, it is must more convenient for the users if the failure is indicated by die()ing: one does not need to check $^E to know that something went wrong. If, however, this solution is not desirable by some reason, the code in question should reset $^E to 0 before making this OS/2 API call, so that the caller of this Perl-accessible function has a chance to distinguish a success-but-0-return value from a failure. (One may return undef as an alternative way of reporting an error.)

  The macros to simplify this type of error propagation are

  `CheckOSError(expr)`

    Returns true on error, sets $^E. Expects `expr()` be a call of `Dos*`-style API.

`CheckWinError(expr)`

  Returns true on error, sets $^E. Expects `expr()` be a call of `Win*`-style API.

`SaveWinError(expr)`

  Returns `expr`, sets $^E from `WinGetLastError()` if `expr` is false.

`SaveCroakWinError(expr,die,name1,name2)`

  Returns `expr`, sets $^E from `WinGetLastError()` if `expr` is false, and die()s if `die` and $^E are true. The message to die is the concatenated strings `name1` and `name2`, separated by `": "` from the contents of $^E.

`WinError_2_Perl_rc`

  Sets `Perl_rc` to the return value of WinGetLastError().

`FillWinError`

  Sets `Perl_rc` to the return value of WinGetLastError(), and sets $^E to the corresponding value.

`FillOSError(rc)`

  Sets `Perl_rc` to `rc`, and sets $^E to the corresponding value.

- Loading DLLs and ordinals in DLLs

  Some DLLs are only present in some versions of OS/2, or in some configurations of OS/2. Some exported entry points are present only in DLLs shipped with some versions of OS/2. If these DLLs and entry points were linked directly for a Perl executable/DLL or from a Perl extensions, this binary would work only with the specified versions/setups. Even if these entry points were not needed, the load of the executable (or DLL) would fail.

  For example, many newer useful APIs are not present in OS/2 v2; many PM-related APIs require DLLs not available on floppy-boot setup.

  To make these calls fail only when the calls are executed, one should call these API via a dynamic linking API. There is a subsystem in Perl to simplify such type of calls. A large number of entry points available for such linking is provided (see `entries_ordinals` - and also `PMWIN_entries` - in os2ish.h). These ordinals can be accessed via the APIs:

        CallORD(), DeclFuncByORD(), DeclVoidFuncByORD(),
        DeclOSFuncByORD(), DeclWinFuncByORD(), AssignFuncPByORD(),
        DeclWinFuncByORD_CACHE(), DeclWinFuncByORD_CACHE_survive(),
        DeclWinFuncByORD_CACHE_resetError_survive(),
        DeclWinFunc_CACHE(), DeclWinFunc_CACHE_resetError(),
        DeclWinFunc_CACHE_survive(), DeclWinFunc_CACHE_resetError_survive()

  See the header files and the C code in the supplied OS/2-related modules for the details on usage of these functions.

  Some of these functions also combine dynaloading semantic with the error-propagation semantic discussed above.

# Perl flavors

Because of idiosyncrasies of OS/2 one cannot have all the eggs in the same basket (though EMX environment tries hard to overcome this limitations, so the situation may somehow improve). There are 4 executables for Perl provided by the distribution:

## perl.exe

The main workhorse. This is a chimera executable: it is compiled as an `a.out`-style executable, but is linked with `omf`-style dynamic library perl.dll, and with dynamic CRT DLL. This executable is a VIO application.

It can load perl dynamic extensions, and it can fork().

Note. Keep in mind that `fork()` is needed to open a pipe to yourself.

## perl_.exe

This is a statically linked `a.out`-style executable. It cannot load dynamic Perl extensions. The executable supplied in binary distributions has a lot of extensions prebuilt, thus the above restriction is important only if you use custom-built extensions. This executable is a VIO application.

This is the only executable with does not require OS/2. The friends locked into `M$` world would appreciate the fact that this executable runs under DOS, Win0.3*, Win0.95 and WinNT with an appropriate extender. See Other OSes.

## perl__.exe

This is the same executable as perl___.exe, but it is a PM application.

Note. Usually (unless explicitly redirected during the startup) STDIN, STDERR, and STDOUT of a PM application are redirected to nul. However, it is possible to see them if you start `perl__.exe` from a PM program which emulates a console window, like Shell mode of Emacs or EPM. Thus it is possible to use Perl debugger (see the perldebug manpage) to debug your PM application (but beware of the message loop lockups - this will not work if you have a message queue to serve, unless you hook the serving into the `getc()` function of the debugger).

Another way to see the output of a PM program is to run it as

      pm_prog args 2>&1 | cat -

with a shell different from cmd.exe, so that it does not create a link between a VIO session and the session of `pm_porg`. (Such a link closes the VIO window.) E.g., this works with sh.exe - or with Perl!

      open P, 'pm_prog args 2>&1 |' or die;
      print while <P>;

The flavor perl__.exe is required if you want to start your program without a VIO window present, but not `detach`ed (run `help detach` for more info). Very useful for extensions which use PM, like `Perl/Tk` or `OpenGL`.

Note also that the differences between PM and VIO executables are only in the default behaviour. One can start any executable in any kind of session by using the arguments `/fs`, `/pm` or `/win` switches of the command `start` (of CMD.EXE or a similar shell). Alternatively, one can use the numeric first argument of the `system` Perl function (see the OS2::Process manpage).

## perl___.exe

This is an `omf`-style executable which is dynamically linked to perl.dll and CRT DLL. I know no advantages of this executable over `perl.exe`, but it cannot `fork()` at all. Well, one advantage is that the build process is not so convoluted as with `perl.exe`.

It is a VIO application.

## Why strange names?

Since Perl processes the `#!`-line (cf. DESCRIPTION in the perlrun manpage, Switches in the perlrun manpage, Not a perl script in the perldiag manpage, No Perl script found in input in the perldiag manpage), it should know when a program is a Perl. There is some naming convention which allows Perl to distinguish correct lines from wrong ones. The above names are almost the only names allowed by this convention which do not contain digits (which have absolutely different semantics).

## Why dynamic linking?

Well, having several executables dynamically linked to the same huge library has its advantages, but this would not substantiate the additional work to make it compile. The reason is the complicated-to-developers but very quick and convenient-to-users ``hard'' dynamic linking used by OS/2.

There are two distinctive features of the dyna-linking model of OS/2: first, all the references to external functions are resolved at the compile time; second, there is no runtime fixup of the DLLs after they are loaded into memory. The first feature is an enormous advantage over other models: it avoids conflicts when several DLLs used by an application export entries with the same name. In such cases ``other'' models of dyna-linking just choose between these two entry points using some random criterion - with predictable disasters as results. But it is the second feature which requires the build of perl.dll.

The address tables of DLLs are patched only once, when they are loaded. The addresses of the entry points into DLLs are guaranteed to be the same for all the programs which use the same DLL. This removes the runtime fixup - once DLL is loaded, its code is read-only.

While this allows some (significant?) performance advantages, this makes life much harder for developers, since the above scheme makes it impossible for a DLL to be ``linked'' to a symbol in the .EXE file. Indeed, this would need a DLL to have different relocations tables for the (different) executables which use this DLL.

However, a dynamically loaded Perl extension is forced to use some symbols from the perl executable, e.g., to know how to find the arguments to the functions: the arguments live on the perl internal evaluation stack. The solution is to put the main code of the interpreter into a DLL, and make the .EXE file which just loads this DLL into memory and supplies command-arguments. The extension DLL cannot link to symbols in .EXE, but it has no problem linking to symbols in the .DLL.

This greatly increases the load time for the application (as well as complexity of the compilation). Since interpreter is in a DLL, the C RTL is basically forced to reside in a DLL as well (otherwise extensions would not be able to use CRT). There are some advantages if you use different flavors of perl, such as running perl.exe and perl__.exe simultaneously: they share the memory of perl.dll.

NOTE. There is one additional effect which makes DLLs more wasteful: DLLs are loaded in the shared memory region, which is a scarse resource given the 512M barrier of the ``standard'' OS/2 virtual memory. The code of .EXE files is also shared by all the processes which use the particular .EXE, but they are ``shared in the private address space of the process''; this is possible because the address at which different sections of the .EXE file are loaded is decided at compile-time, thus all the processes have these sections loaded at same addresses, and no fixup of internal links inside the .EXE is needed.

Since DLLs may be loaded at run time, to have the same mechanism for DLLs one needs to have the address range of any of the loaded DLLs in the system to be available in all the processes which did not load a particular DLL yet. This is why the DLLs are mapped to the shared memory region.

## Why chimera build?

Current EMX environment does not allow DLLs compiled using Unixish `a.out` format to export symbols for data (or at least some types of data). This forces `omf`-style compile of perl.dll.

Current EMX environment does not allow .EXE files compiled in `omf` format to fork(). `fork()` is needed for exactly three Perl operations:

- explicit `fork()` in the script,

- `open FH, "|-"`

- `open FH, "-|"`, in other words, opening pipes to itself.

While these operations are not questions of life and death, they are needed for a lot of useful scripts. This forces `a.out`-style compile of perl.exe.

# ENVIRONMENT

Here we list environment variables with are either OS/2- and DOS- and Win*-specific, or are more important under OS/2 than under other OSes.

## `PERLLIB_PREFIX`

Specific for EMX port. Should have the form

      path1;path2

or

      path1 path2

If the beginning of some prebuilt path matches path1, it is substituted with path2.

Should be used if the perl library is moved from the default location in preference to `PERL(5)LIB`, since this would not leave wrong entries in @INC. For example, if the compiled version of perl looks for @INC in f:/perllib/lib, and you want to install the library in h:/opt/gnu, do

      set PERLLIB_PREFIX=f:/perllib/lib;h:/opt/gnu

This will cause Perl with the prebuilt @INC of

      f:/perllib/lib/5.00553/os2
      f:/perllib/lib/5.00553
      f:/perllib/lib/site_perl/5.00553/os2
      f:/perllib/lib/site_perl/5.00553
      .

to use the following @INC:

      h:/opt/gnu/5.00553/os2
      h:/opt/gnu/5.00553
      h:/opt/gnu/site_perl/5.00553/os2
      h:/opt/gnu/site_perl/5.00553
      .

## `PERL_BADLANG`

If 0, perl ignores `setlocale()` failing. May be useful with some strange locales.

## `PERL_BADFREE`

If 0, perl would not warn of in case of unwarranted free(). With older perls this might be useful in conjunction with the module DB_File, which was buggy when dynamically linked and OMF-built.

Should not be set with newer Perls, since this may hide some real problems.

## `PERL_SH_DIR`

Specific for EMX port. Gives the directory part of the location for sh.exe.

## `USE_PERL_FLOCK`

Specific for EMX port. Since flock(3) is present in EMX, but is not functional, it is emulated by perl. To disable the emulations, set environment variable `USE_PERL_FLOCK=0`.

## `TMP` or `TEMP`

Specific for EMX port. Used as storage place for temporary files.

# Evolution

Here we list major changes which could make you by surprise.

## Text-mode filehandles

Starting from version 5.8, Perl uses a builtin translation layer for text-mode files. This replaces the efficient well-tested EMX layer by some code which should be best characterized as a ``quick hack''.

In addition to possible bugs and an inability to follow changes to the translation policy with off/on switches of TERMIO translation, this introduces a serious incompatible change: before `sysread()` on text-mode filehandles would go through the translation layer, now it would not.

## Priorities

`setpriority` and `getpriority` are not compatible with earlier ports by Andreas Kaiser. See `"setpriority, getpriority"`.

## DLL name mangling: pre 5.6.2

With the release 5.003_01 the dynamically loadable libraries should be rebuilt when a different version of Perl is compiled. In particular, DLLs (including perl.dll) are now created with the names which contain a checksum, thus allowing workaround for OS/2 scheme of caching DLLs.

It may be possible to code a simple workaround which would

- find the old DLLs looking through the old @INC;

- mangle the names according to the scheme of new perl and copy the DLLs to these names;

- edit the internal `LX` tables of DLL to reflect the change of the name (probably not needed for Perl extension DLLs, since the internally coded names are not used for ``specific'' DLLs, they used only for ``global'' DLLs).

- edit the internal `IMPORT` tables and change the name of the ``old'' perl????.dll to the ``new'' perl????.dll.

## DLL name mangling: 5.6.2 and beyond

In fact mangling of extension DLLs was done due to misunderstanding of the OS/2 dynaloading model. OS/2 (effectively) maintains two different tables of loaded DLL:

Global DLLs

  those loaded by the base name from `LIBPATH`; including those associated at link time;

specific DLLs

  loaded by the full name.

When resolving a request for a global DLL, the table of already-loaded specific DLLs is (effectively) ignored; moreover, specific DLLs are always loaded from the prescribed path.

There is/was a minor twist which makes this scheme fragile: what to do with DLLs loaded from

`BEGINLIBPATH` and `ENDLIBPATH`

  (which depend on the process)

. from `LIBPATH`

  which effectively depends on the process (although `LIBPATH` is the same for all the processes).

Unless `LIBPATHSTRICT` is set to `T` (and the kernel is after 2000/09/01), such DLLs are considered to be global. When loading a global DLL it is first looked in the table of already-loaded global DLLs. Because of this the fact that one executable loaded a DLL from `BEGINLIBPATH` and `ENDLIBPATH`, or . from `LIBPATH` may affect which DLL is loaded when another executable requests a DLL with the same name. This is the reason for version-specific mangling of the DLL name for perl DLL.

Since the Perl extension DLLs are always loaded with the full path, there is no need to mangle their names in a version-specific ways: their directory already reflects the corresponding version of perl, and @INC takes into account binary compatibility with older version. Starting from `5.6.2` the name mangling scheme is fixed to be the same as for Perl 5.005_53 (same as in a popular binary release). Thus new Perls will be able to resolve the names of old extension DLLs if @INC allows finding their directories.

However, this still does not guarantee that these DLL may be loaded. The reason is the mangling of the name of the Perl DLL. And since the extension DLLs link with the Perl DLL, extension DLLs for older versions would load an older Perl DLL, and would most probably segfault (since the data in this DLL is not properly initialized).

There is a partial workaround (which can be made complete with newer OS/2 kernels): create a forwarder DLL with the same name as the DLL of the older version of Perl, which forwards the entry points to the newer Perl's DLL. Make this DLL accessible on (say) the `BEGINLIBPATH` of the new Perl executable. When the new executable accesses old Perl's extension DLLs, they would request the old Perl's DLL by name, get the forwarder instead, so effectively will link with the currently running (new) Perl DLL.

This may break in two ways:

- Old perl executable is started when a new executable is running has loaded an extension compiled for the old executable (ouph!). In this case the old executable will get a forwarder DLL instead of the old perl DLL, so would link with the new perl DLL. While not directly fatal, it will behave the same as new executable. This beats the whole purpose of explicitly starting an old executable.

- A new executable loads an extension compiled for the old executable when an old perl executable is running. In this case the extension will not pick up the forwarder - with fatal results.

With support for `LIBPATHSTRICT` this may be circumvented - unless one of DLLs is started from . from `LIBPATH` (I do not know whether `LIBPATHSTRICT` affects this case).

REMARK. Unless newer kernels allow . in `BEGINLIBPATH` (older do not), this mess cannot be completely cleaned. (It turns out that as of the beginning of 2002, . is not allowed, but .\. is - and it has the same effect.)

REMARK. `LIBPATHSTRICT`, `BEGINLIBPATH` and `ENDLIBPATH` are not environment variables, although cmd.exe emulates them on `SET ...` lines. From Perl they may be accessed by the Cwd::extLibpath manpage and the Cwd::extLibpath_set manpage.

## DLL forwarder generation

Assume that the old DLL is named perlE0AC.dll (as is one for 5.005_53), and the new version is 5.6.1. Create a file perl5shim.def-leader with

      LIBRARY 'perlE0AC' INITINSTANCE TERMINSTANCE
      DESCRIPTION '@#perl5-porters@perl.org:5.006001#@ Perl module for 5.00553 -> Perl 5.6.1 forwarder'
      CODE LOADONCALL
      DATA LOADONCALL NONSHARED MULTIPLE
      EXPORTS

modifying the versions/names as needed. Run

     perl -wnle "next if 0../EXPORTS/; print qq(  \"$1\") if /\"(\w+)\"/" perl5.def >lst

in the Perl build directory (to make the DLL smaller replace perl5.def with the definition file for the older version of Perl if present).

     cat perl5shim.def-leader lst >perl5shim.def
     gcc -Zomf -Zdll -o perlE0AC.dll perl5shim.def -s -llibperl

(ignore multiple `warning L4085`).

## Threading

As of release 5.003_01 perl is linked to multithreaded C RTL DLL. If perl itself is not compiled multithread-enabled, so will not be perl's malloc(). However, extensions may use multiple thread on their own risk.

This was needed to compile `Perl/Tk` for XFree86-OS/2 out-of-the-box, and link with DLLs for other useful libraries, which typically are compiled with `-Zmt -Zcrtdll`.

## Calls to external programs

Due to a popular demand the perl external program calling has been changed wrt Andreas Kaiser's port. If perl needs to call an external program via shell, the f:/bin/sh.exe will be called, or whatever is the override, see PERL_SH_DIR.

Thus means that you need to get some copy of a sh.exe as well (I use one from pdksh). The path F:/bin above is set up automatically during the build to a correct value on the builder machine, but is overridable at runtime,

Reasons: a consensus on `perl5-porters` was that perl should use one non-overridable shell per platform. The obvious choices for OS/2 are cmd.exe and sh.exe. Having perl build itself would be impossible with cmd.exe as a shell, thus I picked up `sh.exe`. This assures almost 100% compatibility with the scripts coming from *nix. As an added benefit this works as well under DOS if you use DOS-enabled port of pdksh (see Prerequisites).

Disadvantages: currently sh.exe of pdksh calls external programs via fork()/exec(), and there is no functioning `exec()` on OS/2. `exec()` is emulated by EMX by an asynchronous call while the caller waits for child completion (to pretend that the `pid` did not change). This means that 1 extra copy of sh.exe is made active via fork()/exec(), which may lead to some resources taken from the system (even if we do not count extra work needed for fork()ing).

Note that this a lesser issue now when we do not spawn sh.exe unless needed (metachars found).

One can always start cmd.exe explicitly via

      system 'cmd', '/c', 'mycmd', 'arg1', 'arg2', ...

If you need to use cmd.exe, and do not want to hand-edit thousands of your scripts, the long-term solution proposed on p5-p is to have a directive

      use OS2::Cmd;

which will override system(), exec(), ````, and `open(,'...|')`. With current perl you may override only system(), `readpipe()` - the explicit version of ````, and maybe exec(). The code will substitute the one-argument call to `system()` by `CORE::system('cmd.exe', '/c', shift)`.

If you have some working code for `OS2::Cmd`, please send it to me, I will include it into distribution. I have no need for such a module, so cannot test it.

For the details of the current situation with calling external programs, see Starting OS/2 (and DOS) programs under Perl. Set us mention a couple of features:

- External scripts may be called by their basename. Perl will try the same extensions as when processing -S command-line switch.

- External scripts starting with `#!` or `extproc` will be executed directly, without calling the shell, by calling the program specified on the rest of the first line.

## Memory allocation

Perl uses its own `malloc()` under OS/2 - interpreters are usually malloc-bound for speed, but perl is not, since its malloc is lightning-fast. Perl-memory-usage-tuned benchmarks show that Perl's malloc is 5 times quicker than EMX one. I do not have convincing data about memory footprint, but a (pretty random) benchmark showed that Perl's one is 5% better.

Combination of perl's `malloc()` and rigid DLL name resolution creates a special problem with library functions which expect their return value to be free()d by system's free(). To facilitate extensions which need to call such functions, system memory-allocation functions are still available with the prefix `emx_` added. (Currently only DLL perl has this, it should propagate to perl_.exe shortly.)

## Threads

One can build perl with thread support enabled by providing `-D usethreads` option to Configure. Currently OS/2 support of threads is very preliminary.

Most notable problems:

`COND_WAIT`

  may have a race condition (but probably does not due to edge-triggered nature of OS/2 Event semaphores). (Needs a reimplementation (in terms of chaining waiting threads, with the linked list stored in per-thread structure?)?)

os2.c

  has a couple of static variables used in OS/2-specific functions. (Need to be moved to per-thread structure, or serialized?)

Note that these problems should not discourage experimenting, since they have a low probability of affecting small programs.

# BUGS

This description is not updated often (since 5.6.1?), see ./os2/Changes (perlos2delta) for more info.

# AUTHOR

Ilya Zakharevich, cpan@ilyaz.org

# SEE ALSO

perl(1).

perlos2 - Perl under OS/2, DOS, Win0.3*, Win0.95 and WinNT.