[Bug bootstrap/53779] Bootstrap hangs waiting for a lock

[dje at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53779

--- Comment #1 from Andreas Schwab <schwab@linux-m68k.org> 2012-06-26 14:55:34 UTC ---
Try running it under valgrind.  Your patch is apparently causing a memory
corruption, and the SIGABRT handler tries to call back into malloc/free, which
cannot work.  Most likely target_cost_data is freed twice.

--- Comment #2 from David Edelsohn <dje at gcc dot gnu.org> 2012-06-26 14:56:32 UTC ---
Alan and my patch was to libjava and did not change anything in the common
support for atomics. Unless the build is using libjava at that point, there is
no way for the libjava locks.h patch to affect this.

This may be due to some indirect change in the process memory layout after
Steven's change.

But the real problem appears to libc free() crashing in a call from
var-tracking. libc raises a signal, GCC catching it and tries to print a pretty
error and cleanup before exiting.  The cleanup calls free() again and hangs.

Is there some memory problem in var-tracking or an underlying data structure
that was exposed by Steven's change? Some weird page crossing or some dangling
pointer that accidentally pointed to valid memory before the process layout
changed?