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

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Message-ID: <51C4BB86.1020004@caviumnetworks.com>
Date:	Fri, 21 Jun 2013 13:45:58 -0700
From:	David Daney <ddaney@...iumnetworks.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	David Daney <ddaney.cavm@...il.com>,
	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 06/21/2013 01:22 PM, Oleg Nesterov wrote:
> 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.

Wouldn't that break *all* existing programs that use signals?  Perhaps I 
misunderstand what you are suggesting.

I am proposing that we just reduce the number of usable signals such 
that existing libc status checking macros/functions don't change in any way.

  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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