SIGTRAP during thr_new syscall
dixit at netapp.com
Wed Sep 24 21:34:14 UTC 2008
I am seeing an unexpected SIGTRAP being reported to gdbserver when the
debugged process creates a new thread via the _pthread_create() call of
libthr library. [libthr/thread/thr_create.c,v 220.127.116.11, Freebsd 6.0]
Gdbserver has internally set a breakpoint on address of
_thread_bp_create() so that it gets notified on thread creation and is
expecting a SIGTRAP at address (stop pc) of _thread_bp_create(). But
instead SIGTRAP happens as a side-effect of thr_new() system call and
the stop pc at that point is that of routine thread_start() which is the
starting function of new thread. So gdbserver cannot match expected
breakpoint (ie. _thread_bp_create) and is confused.
For testing purpose, if I call _thread_bp_create() before thr_new() in
_pthread_create(), I get the _expected_ SIGTRAP with address of
_thread_bp_create. But that is not the fix.
Does anyone have any idea about this SIGTRAP being reported to tracing
process gdbserver as part of thr_new? Where is it originating from and why?
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