Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel os linux

[SPARC32]: Fix bug in sparc optimized memset.

Sparc optimized memset (arch/sparc/lib/memset.S) does not fill last
byte of the memory area, if area size is less than 8 bytes and start
address is not word (4-bytes) aligned.

Here is code chunk where bug located:
/* %o0 - memory address, %o1 - size, %g3 - value */
8:
add %o0, 1, %o0
subcc %o1, 1, %o1
bne,a 8b
stb %g3, [%o0 - 1]

This code should write byte every loop iteration, but last time delay
instruction stb is not executed because branch instruction sets
"annul" bit.

Patch replaces bne,a by bne instruction.

Error can be reproduced by simple kernel module:

--------------------
#include <linux/module.h>
#include <linux/config.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <string.h>

static void do_memset(void **p, int size)
{
memset(p, 0x00, size);
}

static int __init memset_test_init(void)
{
char fooc[8];
int *fooi;
memset(fooc, 0xba, sizeof(fooc));

do_memset((void**)(fooc + 3), 1);

fooi = (int*) fooc;
printk("%08X %08X\n", fooi[0], fooi[1]);

return -1;
}

static void __exit memset_test_cleanup(void)
{
return;
}

module_init(memset_test_init);
module_exit(memset_test_cleanup);

MODULE_LICENSE("GPL");
EXPORT_NO_SYMBOLS;
--------------------

Signed-off-by: Alexander Shmelev <ashmelev@task.sun.mcst.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>

authored by

Alexander Shmelev and committed by
David S. Miller
f61698e6 1b64e7ab

+1 -1
+1 -1
arch/sparc/lib/memset.S
··· 162 162 8: 163 163 add %o0, 1, %o0 164 164 subcc %o1, 1, %o1 165 - bne,a 8b 165 + bne 8b 166 166 EX(stb %g3, [%o0 - 1], add %o1, 1) 167 167 0: 168 168 retl