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From: Finn Thain <fthain@linux-m68k.org>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-m68k@lists.linux-m68k.org,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Greg Ungerer <gerg@linux-m68k.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC][CFT] signal handling fixes
Date: Wed, 28 Jul 2021 11:23:24 +1000 (AEST)	[thread overview]
Message-ID: <689cf6b8-e8fc-dc35-9d47-2c3d3e6aafb1@linux-m68k.org> (raw)
In-Reply-To: <YQAbTazP4/JB8Aas@zeniv-ca.linux.org.uk>

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. 

  reply	other threads:[~2021-07-28  1:23 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-25 17:18 Al Viro
2021-07-25 17:19 ` [PATCH 1/3] m68k: handle arrivals of multiple signals correctly Al Viro
2021-09-15 22:08   ` Michael Schmitz
2021-07-25 17:19 ` [PATCH 2/3] m68k: update ->thread.esp0 before calling syscall_trace() in ret_from_signal Al Viro
2021-09-15 22:19   ` Michael Schmitz
2021-07-25 17:20 ` [PATCH 3/3] m68k: leave stack mangling to asm wrapper of sigreturn() Al Viro
2021-09-15 23:35   ` Michael Schmitz
2021-09-16  0:19     ` Al Viro
2021-09-16  0:53       ` Michael Schmitz
2021-09-16  3:21         ` Al Viro
2021-09-16  5:02           ` Michael Schmitz
2021-09-16 16:14             ` Al Viro
2021-07-27 10:21 ` [RFC][CFT] signal handling fixes Finn Thain
2021-07-27 14:42   ` Al Viro
2021-07-28  1:23     ` Finn Thain [this message]
2021-08-11  1:42     ` Finn Thain
2021-09-16  9:03 ` Finn Thain
2021-09-23 14:43   ` Geert Uytterhoeven
2021-09-23 14:45 ` Geert Uytterhoeven

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