linux-kernel - Re: [PATCH v3] kernel/signal.c: fix BUG

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Message-ID: <20130621202244.GA16610@redhat.com>
Date:	Fri, 21 Jun 2013 22:22:44 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	David Daney <ddaney.cavm@...il.com>
Cc:	James Hogan <james.hogan@...tec.com>, linux-kernel@...r.kernel.org,
	Ralf Baechle <ralf@...ux-mips.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	David Daney <david.daney@...ium.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Dave Jones <davej@...hat.com>, linux-mips@...ux-mips.org
Subject: Re: [PATCH v3] kernel/signal.c: fix BUG_ON with SIG128 (MIPS)

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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