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Re: [PATCH v3] kernel/signal.c: fix BUG_ON with SIG128 (MIPS)

To: David Daney <ddaney.cavm@gmail.com>
Subject: Re: [PATCH v3] kernel/signal.c: fix BUG_ON with SIG128 (MIPS)
From: Oleg Nesterov <oleg@redhat.com>
Date: Fri, 21 Jun 2013 22:22:44 +0200
Cc: James Hogan <james.hogan@imgtec.com>, linux-kernel@vger.kernel.org, Ralf Baechle <ralf@linux-mips.org>, Al Viro <viro@zeniv.linux.org.uk>, Andrew Morton <akpm@linux-foundation.org>, Kees Cook <keescook@chromium.org>, David Daney <david.daney@cavium.com>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, David Howells <dhowells@redhat.com>, Dave Jones <davej@redhat.com>, linux-mips@linux-mips.org
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On 06/21, David Daney wrote:
>
> On 06/21/2013 06:39 AM, James Hogan wrote:
>> Therefore add sig_to_exitcode() and exitcode_to_sig() functions which
>> map signal numbers > 126 to exit code 126 and puts the remainder (i.e.
>> sig - 126) in higher bits. This allows WIFSIGNALED() to return true for
>> both SIG127 and SIG128, and allows WTERMSIG to be later updated to read
>> the correct signal number for SIG127 and SIG128.
>
> I really hate this approach.
>
> Can we just change the ABI to reduce the number of signals so that all
> the standard C library wait related macros don't have to be changed?
>
> Think about it, any user space program using signal numbers 127 and 128
> doesn't work correctly as things exist today, so removing those two will
> be no great loss.

Oh, I agree.

Besides, this changes ABI anyway. And if we change it we can do this in
a more clean way, afaics. MIPS should simply use 2 bytes in exit_code for
signal number. Yes, this means we need replace 0x80/0x7f in exit.c by
ifdef'ed numbers. And yes, this means that WIFSIGNALED/etc should be
updated too, but this is also true with this patch.

Oleg.


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