* arei.gong...@huawei.com (arei.gong...@huawei.com) wrote:
> From: ChenLiang <chenlian...@huawei.com>
>
> xbzrle_encode_buffer checks the value in the vm ram repeatedly.
> It is risk if runs xbzrle_encode_buffer on changing data.
> And it is not necessary.
>
> Reported-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
> Signed-off-by: ChenLiang <chenlian...@huawei.com>
> Signed-off-by: Gonglei <arei.gong...@huawei.com>
> ---
> xbzrle.c | 20 +++++++++++++++-----
> 1 file changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/xbzrle.c b/xbzrle.c
> index fbcb35d..bf08c56 100644
> --- a/xbzrle.c
> +++ b/xbzrle.c
> @@ -27,7 +27,7 @@ int xbzrle_encode_buffer(uint8_t *old_buf, uint8_t
> *new_buf, int slen,
> uint8_t *dst, int dlen)
> {
> uint32_t zrun_len = 0, nzrun_len = 0;
> - int d = 0, i = 0;
> + int d = 0, i = 0, j;
> long res, xor;
> uint8_t *nzrun_start = NULL;
>
> @@ -82,6 +82,8 @@ int xbzrle_encode_buffer(uint8_t *old_buf, uint8_t
> *new_buf, int slen,
> if (d + 2 > dlen) {
> return -1;
> }
> + i++;
> + nzrun_len++;
> /* not aligned to sizeof(long) */
> res = (slen - i) % sizeof(long);
> while (res && old_buf[i] != new_buf[i]) {
> @@ -98,11 +100,17 @@ int xbzrle_encode_buffer(uint8_t *old_buf, uint8_t
> *new_buf, int slen,
> xor = *(long *)(old_buf + i) ^ *(long *)(new_buf + i);
> if ((xor - mask) & ~xor & (mask << 7)) {
> /* found the end of an nzrun within the current long */
> - while (old_buf[i] != new_buf[i]) {
> - nzrun_len++;
> - i++;
> + for (j = 0; j < sizeof(long); j++) {
> + if (old_buf[i] != new_buf[i]) {
> + nzrun_len++;
> + i++;
> + } else {
> + break;
> + }
> + }
> + if (j != sizeof(long)) {
> + break;
I wonder if it would be easier just to use the value of 'xor' - since that
already contains the value that we read, and if we've got this far is guaranteed
to have a none-equal byte in it. That would be something like (untested):
for (j = 0; j < sizeof(long); j++) {
if (get_byte(xor, j) != 0) {
break;
}
}
nzrun_len += j;
i += j;
with get_byte being defined as:
uint8_t get_byte(long l, unsigned int index)
{
#ifdef HOST_WORDS_BIGENDIAN
index = (sizeof(long) - 1) - index;
#endif
return (l >> (index * 8)) & 0xff;
}
That way we really aren't reading the data again.
Dave
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
