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Message-ID: <CACRpkdYiOK6853iKpy8bqfGokq5yRBiena8uUYm87L6r0vd6Wg@mail.gmail.com>
Date: Thu, 10 Aug 2023 10:15:33 +0200
From: Linus Walleij <linus.walleij@...aro.org>
To: Kursad Oney <kursad.oney@...adcom.com>
Cc: linux-arm-kernel@...ts.infradead.org,
BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
Russell King <linux@...linux.org.uk>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: memset: cast the constant byte to unsigned char
On Wed, May 17, 2023 at 8:14 PM Kursad Oney <kursad.oney@...adcom.com> wrote:
> memset() description in ISO/IEC 9899:1999 (and elsewhere) says:
>
> The memset function copies the value of c (converted to an
> unsigned char) into each of the first n characters of the
> object pointed to by s.
>
> The kernel's arm32 memset does not cast c to unsigned char. This results
> in the following code to produce erroneous output:
>
> char a[128];
> memset(a, -128, sizeof(a));
>
> This is because gcc will generally emit the following code before
> it calls memset() :
>
> mov r0, r7
> mvn r1, #127 ; 0x7f
> bl 00000000 <memset>
>
> r1 ends up with 0xffffff80 before being used by memset() and the
> 'a' array will have -128 once in every four bytes while the other
> bytes will be set incorrectly to -1 like this (printing the first
> 8 bytes) :
>
> test_module: -128 -1 -1 -1
> test_module: -1 -1 -1 -128
>
> The change here is to 'and' r1 with 255 before it is used.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Kursad Oney <kursad.oney@...adcom.com>
Wow you found this old thing!
Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
Can you please put this into Russell's patch tracker?
https://www.arm.linux.org.uk/developer/
Yours,
Linus Walleij
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