linux-kernel - Re: powerpc: syscall_dotrace() && retcode (Was: powerpc: fork && stepping)

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Date:	Mon, 30 Nov 2009 21:00:56 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Veaceslav Falico <vfalico@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Christoph Hellwig <hch@...radead.org>,
	"Frank Ch. Eigler" <fche@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org, utrace-devel@...hat.com,
	Jan Kratochvil <jan.kratochvil@...hat.com>
Subject: Re: powerpc: syscall_dotrace() && retcode (Was: powerpc: fork &&
	stepping)

On 11/30, Benjamin Herrenschmidt wrote:
>
> On Mon, 2009-11-30 at 10:15 +1100, Benjamin Herrenschmidt wrote:
>
> > Yes, the asm should be changed. I suppose we could check if the result
> > of do_syscall_trace_enter is negative, and if it is, branch to the exit
> > path using r3 as the error code. Would that be ok ?
> >
> > Something like this:
>
> Note however that there's a trace exit too and that's normally the right
> place to alter the result don't you think ?

Yes, the result can be changed when the tracee reports syscall-exit.

Should powerpc allow this on syscall-entry? I do not know. x86 does,
and we have this test-case which assumes powerpc should allow too.
But when it comes to ptrace I can almost never know what was the
supposed behaviour/api.

Jan, Roland, what do you think?

Oleg.

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