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

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Message-ID: <18226.39815.631891.784259@cargo.ozlabs.ibm.com>
Date:	Thu, 8 Nov 2007 16:15:51 +1100
From:	Paul Mackerras <paulus@...ba.org>
To:	David Miller <davem@...emloft.net>
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.

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.

Paul.
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