= Common tasks and useful tips for porting Unix software to OS/2 =

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This page explains some common code changes often necessary to make Unix software work properly on OS/2. These changes are mainly related to various components shared among Unix programs. These changes are tracked here since we don't normally push upstream and hence we should apply them in each new project that we port and that uses these components.

== Common tasks ==

=== Fix POTFILES generation ===

The fix is applied to `po.m4` that creates rules for `POTFILES` generation. Unfortunately, the upstream version doesn't take DOS drive letters into account and hence creates incorrect relative paths in the generated `POTFILES` file (like `../D:/Coding/myproject/trunk/...`). Here is a typical fix: r1009. When applied, `configure` and friends need to be regenerated in the source tree and then `configure` needs to be re-run to generate proper `Makefile`s.

=== Fix HAVE_ICONV detection ===

The fix is applied to `iconv.m4` that detects if the `HAVE_ICONV` config.h macro should be set or not. Here is a typical fix: r1023 (originally this: r934). When applied, `configure` and friends need to be regenerated in the source tree and then `configure` needs to be re-run to generate a proper `config.h`.

=== Fix EOLs in git-version-gen ===

Some projects use the `build-aux/git-version-gen` script to define the project version in `configure.ac`. The "stock" version of this script doesn't understand CRLF as line terminators which leads to a corrupt `configure`. The fix is rather simple and can be seen here: r968.

=== Fix OS/2 DLL name in libtool ===

When `libtool` is used to generate project DLLs, such a DLL often gets a version number in its name (e.g. `libpixman-1.so.0`, where `pixman-1` is the  base DLL name and `0` is the major version number). However, on OS/2 the version information cannot follow the extension and hence it must be put into the name part. But the name part is limited to 8 chars so `libtool` has to cut the base DLL name by default to make the appended major version number fit the limit. In case of the `pixman` this would give us `pixman-0.dll` which looks misleading (the correct name is `pixman10.dll` in this case).

A proper solution here is to force `libtool` use a special, short version of the base name for the DLL file (and only for it — all other files, such as the import library name, should carry the original name so that the linker can find it). This is done using the `-shortname` libtool option. Where to add it varies from project to project but the typical place is the _la_LDFLAGS variable in `Makefile.am` for the library. See r1232 for a real-life example.

=== Have libtool add a buildlevel string to the DLL ===

With the latest `libtool` it is possible to have a buildlevel string built into a dll. To do so you need to teach the `Makefile` how to handle it. Most likely it is the best practice to change `Makefile.am` and then do a `sh -c "autoreconf -fvi"`. How to adjust a `Makefile.am` can be seen here: r1823 

=== Increase default stack file for executables ===

The default stack size in the EMX GCC tool chain is 1 Mbyte. This is not always enough. A clear indication of your program running out of stack is a crash in GCC1.DLL (in a stack checking function `___chkstk_ms` usually located at 0001:00000F4).

The stack size can be increased using the `-Zstack` linker option which specifies the stack size in Kbytes. For example, passing `-Zstack 0x2000` to the linker (e.g. via LDFLAGS) will increase the stack size to 8 Mbytes. Read the next section if you want to change the stack size using LDFLAGS in an Autoconf-based project.

=== Add OS/2 specific build details to Autoconf-based projects ===

**Method 1**. If `configure.ac` already uses AC_CANONICAL_TARGET or AC_CANONICAL_HOST macros, then you can add the following excerpt to it to do OS/2-specific job (`$target_os` becomes `$host_os` if AC_CANONICAL_HOST is used instead of AC_CANONICAL_TARGET):

{{{
case "$host_os" in
os2*)
	# Increase stack size to 8MB
	export LDFLAGS="$LDFLAGS -Zstack 0x2000"
esac
}}}

**Method 2**. If the above AC_CANONICAL macros are not used, then it will be simpler to use `uname` to do the OS/2-specific job:

{{{
case `uname -s 2>/dev/null` in
OS/2)
	# Increase stack size to 8MB
	export LDFLAGS="$LDFLAGS -Zstack 0x2000"
esac
}}}

Note though that if you need to add such a block more than once, it makes sense to add AC_CANONICAL_TARGET right after AC_INIT to `configure.ac` and go with //Method 1// described above.