Messages in this thread | | | Date | Wed, 28 Jul 2021 11:23:24 +1000 (AEST) | From | Finn Thain <> | Subject | Re: [RFC][CFT] signal handling fixes |
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On Tue, 27 Jul 2021, Al Viro wrote:
> On Tue, Jul 27, 2021 at 08:21:52PM +1000, Finn Thain wrote: > > On Sun, 25 Jul 2021, Al Viro wrote: > > > > > > > > The series is on top of 5.14-rc1; it lives in > > > git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git #untested.m68k > > > Individual patches in followups... > > > > > > _Very_ lightly tested on aranym; no real hardware to test it on. > > > Any help with review and testing would be very welcome. > > > > > > > I can test this branch on a Motorola 68040 machine I have here. Can you > > advise how to get decent code coverage? Maybe there's a package out there > > with a signal-heavy test suite? Maybe I need a break point in a signal > > handler? Or perhaps just send ^C to a process running under strace? > > Generally, SIGINT is not the best insertion vector... >
True. I see that 'man 7 signal' says that SIGQUIT will produce a coredump. Would that contain anything of interest?
> Set a handler of e.g. SIGALRM with sigaction(), with a couple of other signals > in sa_mask (e.g. SIGUSR1 and SIGUSR2). With raise() on those inside the > SIGALRM handler - then they will become deliverable on return from handler. > And have SIGUSR1 and SIGUSR2 handlers print siginfo and ucontext contents > (have them set with SA_SIGINFO in sa_flags, look at the second and third > arguments of sighandler). > > Use alarm(2) to arrange for SIGALRM and sit in a tight loop - that'll give you > delivery on return from interrupt. Alternatively, raise(SIGALRM) will give > you delivery on return from trap. And making that a SIGBUS handler instead, > mmapping a file, truncating it to 0 and dereferencing something in mmapped > area will give you delivery on return from access error trap. Division by > zero (and insertion handler on SIGFPE) ought to give you a type 2 exception > stack frame (4 bytes of aux data, that makes shifted exception frame bugger > format and vector fields of the original). > > FWIW, the third argument of handler points to > struct ucontext { > unsigned long uc_flags; > struct ucontext *uc_link; > stack_t uc_stack; > struct mcontext uc_mcontext; > unsigned long uc_filler[80]; > sigset_t uc_sigmask; /* mask last for extensibility */ > }; > and type/vector is stored in uc_filler[54] (216 bytes into the array), with > aux data from exception stack frame starting from uc_filler[55]. >
OK, give me a week or so and I'll see what I can come up with.
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