linux-kernel - Re: compat_sys_times() bogus until jiffies >= 0.

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Message-Id: <20071107.222406.90744682.davem@davemloft.net>
Date:	Wed, 07 Nov 2007 22:24:06 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	paulus@...ba.org
Cc:	akpm@...ux-foundation.org, lkml@...idb.org,
	linux-kernel@...r.kernel.org, drepper@...hat.com,
	mtk-manpages@....net
Subject: Re: compat_sys_times() bogus until jiffies >= 0.

From: Paul Mackerras <paulus@...ba.org>
Date: Thu, 8 Nov 2007 16:15:51 +1100

> David Miller writes:
> 
> > I can't see where x86 is doing this though, so perhaps for x86
> > glibc does make the negative value check.  But I doubt it is
> > checking the range 0x80000000-0xffffffff, otherwise mmap() would
> > be busted.
> 
> At least for the INTERNAL_SYSCALL macro in glibc, the error check is:
> 
> #define INTERNAL_SYSCALL_ERROR_P(val, err) \
>   ((unsigned int) (val) >= 0xfffff001u)
> 
> in sysdeps/unix/sysv/linux/i386/sysdep.h.  Similarly the PSEUDO macro
> in that file does a cmpl $-4095,%eax to test for error.  (There is also
> a PSEUDO_NOERRNO which doesn't test for error.)
> 
> So the convention on (32-bit) x86 is that -4095 .. -1 are error
> values, and other values are successful return values.

Thanks for figuring that out.

Really there is no way to fix sys_times() return values
universally.  Each proposed solution either doesn't fix
the problem, or adds a new failure mode.
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