On Thu, Oct 31, 2013 at 03:39:18PM +0100, Jan Kratochvil wrote: > On Thu, 31 Oct 2013 11:28:14 +0100, Jan Kratochvil wrote: > > Calling backtrace() for the first time also is not signal-safe: > > glibc/sysdeps/x86_64/backtrace.c init() calls __libc_dlopen(). > > Maybe xorg could call backtrace() just during init to get backtrace() > > initialized, I am not completely sure it will be signal-safe then but it > > may be. > > That initialization is already done in xserver as shown by Adam Jackson: > > http://cgit.freedesktop.org/xorg/xserver/commit/?id=0b131a5cd91cea54240777c66a9cd385029e8cb2 > > > > To get .symtab symbols resolution the only safe way is to do fork()+exec(). > > Surprisingly libunwind is mostly signal-safe, similarly like backtrace() is. > As pointer out by Jakub Jelinek, they are not completely safe wrt > _dl_load_lock dependency of dl_iterate_phdr() which is used by both. > But that should not matter too much in practice for xserver. > > I would still find safer to run external backtracer via fork()+exec() than > doing the whole backtrace from SIGSEGV handler, for example due to memory > corruption inside xserver. > > That is without fork()+exec() libunwind is currently the best there is for > xserver.
ok, in that case I'll leave libunwind in for the time being because right now I don't really have the time to work around this otherwise. Cheers, Peter _______________________________________________ [email protected]: X.Org development Archives: http://lists.x.org/archives/xorg-devel Info: http://lists.x.org/mailman/listinfo/xorg-devel
