From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4C062246.40107@domain.hid> Date: Wed, 02 Jun 2010 11:20:06 +0200 From: Jan Kiszka MIME-Version: 1.0 References: <20100601135005.GA5483@domain.hid> <1275402757.27918.151.camel@domain.hid> <20100601155403.GA8240@domain.hid> <4C053C51.4090903@domain.hid> <4C061823.70005@domain.hid> <1275470136.18250.16.camel@domain.hid> In-Reply-To: <1275470136.18250.16.camel@domain.hid> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-help] Handling Linux Signals in primary domain context List-Id: Help regarding installation and common use of Xenomai List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Philippe Gerum Cc: "xenomai@xenomai.org" Philippe Gerum wrote: > On Wed, 2010-06-02 at 10:36 +0200, Gilles Chanteperdrix wrote: >> Jan Kiszka wrote: >>> Tschaeche IT-Services wrote: >>>> On Tue, Jun 01, 2010 at 04:32:37PM +0200, Philippe Gerum wrote: >>>>> Not in the absence of syscall. We thought about this once already, when >>>>> considering how a watchdog preempting a runaway task in primary mode >>>>> could force a secondary mode switch: there is no sane and easy solution >>>>> to this unfortunately. >>>> This is exactly Sigmatek's problem: Our customers develop code >>>> within our debugging/development environment. We want to catch >>>> this situation (the developer implements a while(1)) with a >>>> watchdog throwing SIGTRAP so that our debugger gets active >>>> and can locate the problem according to the stack frame... >>> CONFIG_XENO_OPT_WATCHDOG is probably what you are looking for. It tries >>> to catch "well-behaving" broken threads via SIGDEBUG and kills the >>> hopelessly broken rest - system alive again. >>> >>> You can then debug the former and need to do code review on the latter. >>> Or you could also try to add some loop-breaking Xenomai syscalls (or >>> even more clever checks) to library services the code under suspect >>> usually invokes. >> I am afraid "well-behaving" means emitting syscalls. We have a radical >> way to cause a SIGSEGV to be sent to a thread having run amok: set its >> PC to an invalid address (after having printed the real PC). gdb will >> not be able to print where the program stopped, but should be able to >> print the backtrace. >> > > Actually, we could extend this logic and forge a stack frame to return > to the preempted application code via some userland trampoline code, > doing the switch: > > [watchdog trigger] > forge_return_frame(on =regs->sp, to =regs->pc); > regs->pc = __oops_I_did_it_again; > > __oops_I_did_it_again: > __xn_migrate(LINUX_DOMAIN); > ret (via forged frame) Yep, that's what came to my mind as well. But the __oops_I_did_it_again part has to reside in user space, no? > > The thing is, that this brings in some arch-dep code to forge a stack > frame (like the kernel uses for signals), that should rather live in the > pipeline core. Actually, we are then close to enabling signal delivery outside syscalls... Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux