[Spice-devel] [PATCH spice-server 10/10] utils: Avoid possible unaligned access

[Frediano Ziglio]

Code in rgb32_data_has_alpha possibly generate this warning using
clang:

utils.c:35:16: error: cast from 'uint8_t *' (aka 'unsigned char *') to 'uint32_t *' (aka 'unsigned int *') increases required alignment from 1 to 4 [-Werror,-Wcast-align]
        line = (uint32_t *)data;
               ^~~~~~~~~~~~~~~~

Although the images are expected to be all aligned in this respect
use byte access on the data instead. This, beside fixing the alignment
issue also avoid problem with big endian machines (images in SPICE are
expected to have the alpha channel as the forth byte).

Signed-off-by: Frediano Ziglio <fziglio at redhat.com>
---
 server/utils.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/server/utils.c b/server/utils.c
index 1856db61..b8a40b1d 100644
--- a/server/utils.c
+++ b/server/utils.c
@@ -27,25 +27,25 @@
 int rgb32_data_has_alpha(int width, int height, size_t stride,
                          const uint8_t *data, int *all_set_out)
 {
-    const uint32_t *line, *end;
-    uint32_t alpha;
+    const uint8_t *line, *end;
+    uint8_t alpha;
     int has_alpha;
 
     has_alpha = FALSE;
     while (height-- > 0) {
-        line = (const uint32_t *)data;
-        end = line + width;
+        line = data;
+        end = line + sizeof(uint32_t) * width;
         data += stride;
         while (line != end) {
-            alpha = *line & 0xff000000U;
+            alpha = line[3];
             if (alpha != 0) {
                 has_alpha = TRUE;
-                if (alpha != 0xff000000U) {
+                if (alpha != 0xffU) {
                     *all_set_out = FALSE;
                     return TRUE;
                 }
             }
-            line++;
+            line += sizeof(uint32_t);
         }
     }
 
-- 
2.14.3