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

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 Makefiles.

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.

Debugging techniques

Using a logging LIBC DLL

Modern OS/2 programs are built with GCC which uses ​kLIBC as its POSIX-like C runtime library. This library provides a powerful logging facility where it logs a lot of internal actions as well as entry and exit from each public function it provides. Sometimes, especially when debugging application crashes that can't be caught by other means, it is very handy to get this logging for your application.

There are several versions of the LIBC DLL in each release. The normal version, LIBCxyz.dll, is an optimized build that doesn't provide any logging or debug info. The logging version is called LIBCxyz.logchk. In the RPM environment this DLL lives in the libc-devel package. In order to use it in place of the normal version, do the following:

1. Make sure you have LIBCxyz.logchk installed and that xyz matches the version of LIBC you normally use.
2. Put this fragment to your CONFIG.SYS:

   REM // Disable all LIBC logging in the logchk dll by default
   SET LIBC_LOGGING=-ALL
   

3. Unlock LIBCxyz.dll and rename it to LIBCxyz.dll.normal.
4. Rename LIBCxyz.logchk to LIBCxyz.dll.
5. Reboot.

Note that this will cause all applications linked against LIBCxyz.dll to create a log file named libc-ABCD.log in the application's current directory where ABCD is a hex number of a running process. Given that we disabled all logging by SET LIBC_LOGGING=-ALL in CONFIG.SYS, these files will only contain a small log header and won't grow at runtime — this is done to avoid excessive logging for unneeded applications and unnecessary slowdown caused by this logging.

In order to get anything useful in the log file, you need to enable logging for your application. This is done by overriding the LIBC_LOGGING environment variable before starting it. To enable full logging, just do

SET LIBC_LOGGING=+ALL

before starting the application. Not that this will produce a huge amount of logs especially if your application starts other processes which will also have all logging enabled. You may fine-tune what to log using log groups as defined in ​http://svn.netlabs.org/repos/libc/branches/libc-0.6/src/emx/src/lib/sys/logstrict.c (look for aDefGrps). For example, in order to enable all but I/O logging, you do

SET LIBC_LOGGING=+ALL-IO

If you want to go back to the normal LIBC version, just unlock LIBCxyz.dll, rename it back to LIBCxyz.logchk, rename LIBCxyz.dll.normal to LIBCxyz.dll and reboot.

Note that while technically you could copy LIBCxyz.logchk to a separate directory, rename it to LIBCxyz.dll there and then set BEGINLIBPATH=<DIR> and LIBPATHSTRICT=T in the environment to have this version of LIBC used for your process without rebooting, this will not work well. Doing so will lead to having two different LIBC copies in memory which don't cooperate because of the LIBC design that assumes there is only one active LIBC DLL at a time. In particular, having more than one DLL in memory is known to make forked children crash with some weird errors (even if one manages to separate shared structures of different LIBC versions by using unique mutex and shared memory names).