linux-kernel - Re: [PATCH] arm: memset: zero out upper bytes in r1

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Message-ID: <loom.20140508T095105-952@post.gmane.org>
Date:	Thu, 8 May 2014 08:04:44 +0000 (UTC)
From:	Vladimir Murzin <murzin.v@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm: memset: zero out upper bytes in r1

Andrey Ryabinin <a.ryabinin <at> samsung.com> writes:

> 
> memset doesn't work right for following example:
> 
> 	signed char c = 0xF0;
> 	memset(addr, c, size);
> 
> Variable c is signed, so after typcasting to int the value will be 0xFFFFFFF0.
> This value will be passed through r1 regitster to memset function.
> memset doesn't zero out upper bytes in r1, so memory will be filled
> with 0xFFFFFFF0 instead of expected 0xF0F0F0F0.

It behaves the same as a generic implementation in lib/string.c, moreover
gcc built-in behaves the same. So it looks like expected behavior and POSIX
Programmer's Manual (man 3posix memset) explicitly says that "c" is
converted to unsigned char.

Cheers
Vladimir

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