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Allow not saving the signal state in SIGSETJMP

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Saving the signal state is very slow (this patch is a 14% speedup).  The
reason we need this code is because signal handler will leave the
signal blocked when we longjmp out of it.  But in this case we can
just manually unblock the signal instead of taking the unconditional
perf hit.

gdb/ChangeLog:

2019-10-16  Christian Biesinger  <cbiesinger@google.com>

	* gdbsupport/gdb_setjmp.h (SIGSETJMP): Allow passing in the value to
	pass on to sigsetjmp's second argument.
	* cp-support.c (gdb_demangle): Unblock SIGSEGV if we caught a crash.

Change-Id: Ib3010966050c64b4cc8b47d8cb45871652b0b3ea
This commit is contained in:
Christian Biesinger
2019-10-15 10:02:33 -05:00
parent 950b74950f
commit 17bfe554b9
3 changed files with 28 additions and 3 deletions
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19
gdb/cp-support.c
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@@ -1539,7 +1539,16 @@ gdb_demangle (const char *name, int options)
ofunc = signal (SIGSEGV, gdb_demangle_signal_handler);
#endif
crash_signal = SIGSETJMP (gdb_demangle_jmp_buf);
/* The signal handler may keep the signal blocked when we longjmp out
of it. If we have sigprocmask, we can use it to unblock the signal
afterwards and we can avoid the performance overhead of saving the
signal mask just in case the signal gets triggered. Otherwise, just
tell sigsetjmp to save the mask. */
#ifdef HAVE_SIGPROCMASK
crash_signal = SIGSETJMP (gdb_demangle_jmp_buf, 0);
#else
crash_signal = SIGSETJMP (gdb_demangle_jmp_buf, 1);
#endif
}
#endif
@@ -1559,6 +1568,14 @@ gdb_demangle (const char *name, int options)
{
static int error_reported = 0;
#ifdef HAVE_SIGPROCMASK
/* If we got the signal, SIGSEGV may still be blocked; restore it. */
sigset_t segv_sig_set;
sigemptyset (&segv_sig_set);
sigaddset (&segv_sig_set, SIGSEGV);
sigprocmask (SIG_UNBLOCK, &segv_sig_set, NULL);
#endif
if (!error_reported)
{
std::string short_msg