Re: linuxthreads 2.2.2 causes SEGV

[Dan Maas]

Greetings all, I am homing in on the cause of this problem (segfault inside
__pthread_alt_lock() at startup time with any program linked to
libpthread.so).

The immediate cause is __pthread_alt_lock() trying to get thread_self() by
reading from the descriptor struct pointed to by 'gs'... On my system, 'gs'
is 0x0 (NULL) when this happens, so, kaboom. Here's the backtrace:

#0  0x40030e7a in __pthread_alt_lock () from /lib/libpthread.so.0
#1  0x4002e46f in pthread_mutex_lock () from /lib/libpthread.so.0
#2  0x4016e56b in __register_frame_info (begin=0x401858b8, ob=0x40187760)
                                       at ../../gcc/frame.c:581
#3  0x4007f13e in __libc_global_ctors () from /lib/libc.so.6
#4  0x4007f1ee in init () from /lib/libc.so.6
#5  0x4000e9cf in call_init () from /lib/ld-linux.so.2
#6  0x4000eb2e in _dl_init () from /lib/ld-linux.so.2

I believe the root cause is incorrect startup/initialization order. The 'gs'
register must be set up (by __pthread_initialize_minimal) *BEFORE* any other
pthread functions execute. But on my system, __register_frame_info() tries
to call pthread_mutex_lock() before initialize_minimal() executes.

So to fix this we need to make sure pthread_mutex_lock() does NOT get called
until AFTER __pthread_initialize_minimal()... I'm not sure how to do this,
help would be appreciated.

FYI, I am using gcc 2.95.3 (final), kernel 2.4.2, and glibc 2.2.2 (compiled
for 2.4.x kernels only, and i686 only -- obviously this problem is specific
to LDT-based pthreads).

Regards,
Dan