From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Tue, 13 Nov 2007 14:03:44 +0000 (GMT) Received: from localhost.localdomain ([127.0.0.1]:64134 "EHLO dl5rb.ham-radio-op.net") by ftp.linux-mips.org with ESMTP id S20026526AbXKMODm (ORCPT ); Tue, 13 Nov 2007 14:03:42 +0000 Received: from denk.linux-mips.net (denk.linux-mips.net [127.0.0.1]) by dl5rb.ham-radio-op.net (8.14.1/8.13.8) with ESMTP id lADE0bJQ007714; Tue, 13 Nov 2007 14:00:57 GMT Received: (from ralf@localhost) by denk.linux-mips.net (8.14.1/8.14.1/Submit) id lADE0aD7007713; Tue, 13 Nov 2007 14:00:36 GMT Date: Tue, 13 Nov 2007 14:00:36 +0000 From: Ralf Baechle To: Franck Bui-Huu Cc: Andrew Haley , David Daney , linux-mips@linux-mips.org, Richard Sandiford , gcc@gcc.gnu.org Subject: Re: Cannot unwind through MIPS signal frames with ICACHE_REFILLS_WORKAROUND_WAR Message-ID: <20071113140036.GA7650@linux-mips.org> References: <473957B6.3030202@avtrex.com> <18233.36645.232058.964652@zebedee.pink> <20071113121036.GA6582@linux-mips.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.14 (2007-02-12) Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 17482 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: ralf@linux-mips.org Precedence: bulk X-list: linux-mips On Tue, Nov 13, 2007 at 02:14:58PM +0100, Franck Bui-Huu wrote: > > > David Daney writes: > > > > With the current kernel (2.6.23.1) in my R5000 based O2 it seems > > > > impossible for GCC's exception unwinding machinery to unwind through > > > > signal frames. The cause of the problems is the > > > > ICACHE_REFILLS_WORKAROUND_WAR which puts the sigcontext at an almost > > > > impossible to determine offset from the signal return trampoline. The > > > > unwinder depends on being able to find the sigcontext given a known > > > > location of the trampoline. > > > > > > > > It seems there are a couple of possible solutions: > > > > > > > > 1) The comments in war.h indicate the problem only exists in R7000 > > > > and E9000 processors. We could turn off the workaround if the > > > > kernel is configured for R5000. That would help me, but not those > > > > with the effected systems. > > > > > > > > 2) In the non-workaround case, the siginfo immediately follows the > > > > trampoline and the first member is the signal number. For the > > > > workaround case the first word following the trampoline is zero. > > > > We could replace this with the offset to the sigcontext which is > > > > always a small negative value. The unwinder could then distinguish > > > > the two cases (signal numbers are positive and the offset > > > > negative). If we did this, the change would have to be coordinated > > > > with GCC's unwinder (in libgcc_s.so.1). > > > > > > > > Thoughts? > > > > > > The best solution is to put the unwinder info in the kernel. Does > > > MIPS use a vDSO ? > > > > No though we should. > > > > Another reason is to get rid of the classic trampoline the kernel installs > > on the stack. On some multiprocessor systems it requires a cacheflush > > operation to be performed on all processors which is expensive. Having > > the trampoline in a vDSO would solve that. > > > > And the stack wouldn't need to have exec permission anymore. Oh? extern void frob(void (*)(void)); int foo(void) { int x; void bar(void) { x++; } frob(&bar); print("x is %d\n", x); } Compile and enjoy. Ralf