[Swfdec] The Cautionary Tale of Multi-Arch glib

[Nick Zitzmann]

I'm mainly writing this in hopes that it gets picked up by Google in  
case anyone else runs into this problem.

I was going to distribute the source & binaries for the first sneaky- 
peek at Swfdec for Mac OS X today. But yesterday, when I tried running  
my player application within Mac OS X's PowerPC emulator (Rosetta), I  
noticed it was crashing in some animations with the following stderr  
output:

GThread-ERROR **: file gthread-posix.c: line 197  
(g_mutex_trylock_posix_impl): error 'Invalid argument' during  
'pthread_mutex_trylock'

Of course, this wasn't happening in the Intel build, only PPC. And I  
can't ship a binary that's going to be unstable on many users'  
computers. So I searched Google and found several other people who had  
run into this problem, but no one had a solution.

Then I remembered that glib writes out one very CPU-specific header  
file, glibconfig.h, that includes everything from byte-swapping macros  
to the structure of a pthread mutex. I knew from previous experience  
that the file was very different when building for X86-64 than it was  
on X86, but then I forgot that it was probably different between X86  
and PPC as well.

One of the more interesting features of Mac OS X's Mach-O ABI is the  
ability to include code for multiple architectures in a single  
executable. But the GNU build system was set up under the assumption  
that nobody ever did this, which was probably a safe assumption to  
make in the early '90s, but is kind of dated now. Nevertheless, I was  
building glib by setting multiple architectures in CFLAGS and  
disabling autoconf dependencies, trying to weasel around this  
restriction, which resulted in a glibconfig.h file with a little- 
endian mutex format, which is what was causing the crash.

So I had to build glib manually three times, once for PPC, once for  
X86, and once for X86-64, and then manually mash the glibconfig.h and  
binaries together. Which is incredibly tedious, since it can't be  
automated (at least, not the glibconfig.h part). I didn't even bother  
with a PPC64 build. But once I did this, then the player quit  
crashing, and world peace was realized.

If you're reading this through Google, I hope this helped you...

Oh, yes, and I'll now release the source & binaries next Monday during  
prime-time. Maybe now I'll have some time to figure out how to decode  
video with ffmpeg directly...

Nick Zitzmann
<http://seiryu.home.comcast.net/>
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