linux-kernel - Re: [PATCHSET ptrace] ptrace: implement PTRACE_SEIZE/INTERRUPT and group stop notification, take#4

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Message-Id: <201106031125.16071.pedro@codesourcery.com>
Date:	Fri, 3 Jun 2011 11:25:15 +0100
From:	Pedro Alves <pedro@...esourcery.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	Oleg Nesterov <oleg@...hat.com>, jan.kratochvil@...hat.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, indan@....nu, bdonlan@...il.com
Subject: Re: [PATCHSET ptrace] ptrace: implement PTRACE_SEIZE/INTERRUPT and group stop notification, take#4

On Friday 03 June 2011 02:24:45, Tejun Heo wrote:
> > > * What to do about events which are reported by genuine SIGTRAP
> > >  generation?
> > 
> > I don't understand what you meant here. Example(s)?
> 
> The syscall, breakpoint, single step SIGTRAPs which can't be
> distinguished from userland generated SIGTRAPs and may be mixed and/or
> lost.  Maybe it's best to leave them alone or maybe we can add some
> way to distinguish them which is mostly backward compatible (which is
> enabled w/ SEIZE and hopefully doesn't require noticeable userland
> changes).

Some archs started encoding some of that stuff on SIGTRAPs si_code.
E.g., on a ppc box I got here, I see:

/* `si_code' values for SIGTRAP signal.  */
enum
{
  TRAP_BRKPT = 1,               /* Process breakpoint.  */
# define TRAP_BRKPT     TRAP_BRKPT
  TRAP_TRACE                    /* Process trace trap.  */
# define TRAP_TRACE     TRAP_TRACE
};

It'd be _very_ useful for x86 (and others) to have
something like TRAP_BRKPT for int3.  Both for ptracers
and in-process self debuggers.

I'd be super happy to be told we have that already
in recent kernels and I missed it.  :-)

-- 
Pedro Alves
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