Googling this problem doesn't show many people complaining, so I'm 
wondering if it's just something wrong with my system.

So, simply put:

int main() { abort(); }

Running it and getting backtrace gives:

#0  0xb7ebdee9 in raise () from /lib/tls/libc.so.6
#1  0xb7fcbedc in ?? () from /lib/tls/libc.so.6
#2  0xbffff3f0 in ?? ()
#3  0xb7ebf781 in abort () from /lib/tls/libc.so.6
#4  0x00000000 in ?? ()
#5  0x00000020 in ?? ()
..
#37 0xb8000c40 in ?? () from /lib/ld-linux.so.2
#38 0xb7fe919c in ?? ()
#39 0x08048217 in ?? ()
#40 0xbffff3d8 in ?? ()
#41 0xb7ff23cf in _dl_lookup_versioned_symbol () from /lib/ld-linux.so.2
#42 0xb7ea97f8 in __libc_start_main () from /lib/tls/libc.so.6
#43 0xb7fcbedc in ?? () from /lib/tls/libc.so.6

Not very helpful. Sometimes it gives almost usable backtrace by losing 
only the first 5 functions, but sometimes it's entirely corrupted.

First this happened with Linux 2.6.5, gdb 6.0 and gcc 3.something. I 
went back to 2.4 kernel. Today I thought maybe it would be fixed by 
now, but it still happens with 2.6.9-rc2-mm1, gdb 6.2.1 and gcc 3.3.4 
(from Debian unstable). CPU is Athlon XP.

Is this kernel or gdb problem?