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

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Date:	Thu, 8 May 2014 08:38:46 +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

Vladimir Murzin <murzin.v <at> gmail.com> writes:

> 
> 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
> 
> 

Sorry, had a bad coffee when posted it ;) It behaves /different/, but it is
here for many years... doesn't this change break something? iow, it possible
that some user rely on this behavior...

Vladimir



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