• Kursad Oney's avatar
    ARM: 9321/1: memset: cast the constant byte to unsigned char · c0e82466
    Kursad Oney authored
    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: 1da177e4 ("Linux-2.6.12-rc2")
    Reviewed-by: default avatarArd Biesheuvel <ardb@kernel.org>
    Reviewed-by: default avatarLinus Walleij <linus.walleij@linaro.org>
    Signed-off-by: default avatarKursad Oney <kursad.oney@broadcom.com>
    Signed-off-by: default avatarRussell King (Oracle) <rmk+kernel@armlinux.org.uk>
    c0e82466
memset.S 2.91 KB