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Diffstat (limited to 'checksum.c')
-rw-r--r--checksum.c19
1 files changed, 14 insertions, 5 deletions
diff --git a/checksum.c b/checksum.c
index f2b82a4..03b8a7c 100644
--- a/checksum.c
+++ b/checksum.c
@@ -69,8 +69,17 @@
*
* Return: 32-bit sum of 16-bit words
*/
+/* Type-Based Alias Analysis (TBAA) optimisation in gcc 11 and 12 (-flto -O2)
+ * makes these functions essentially useless by allowing reordering of stores of
+ * input data across function calls. Not even declaring @in as char pointer is
+ * enough: disable gcc's interpretation of strict aliasing altogether. See also:
+ *
+ * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106706
+ * https://stackoverflow.com/questions/2958633/gcc-strict-aliasing-and-horror-stories
+ * https://lore.kernel.org/all/alpine.LFD.2.00.0901121128080.6528__33422.5328093909$1232291247$gmane$org@localhost.localdomain/
+ */
/* NOLINTNEXTLINE(clang-diagnostic-unknown-attributes) */
-__attribute__((optimize("-fno-strict-aliasing"))) /* See siphash_8b() */
+__attribute__((optimize("-fno-strict-aliasing")))
uint32_t sum_16b(const void *buf, size_t len)
{
const uint16_t *p = buf;
@@ -110,7 +119,7 @@ uint16_t csum_fold(uint32_t sum)
* Return: 16-bit IPv4-style checksum
*/
/* NOLINTNEXTLINE(clang-diagnostic-unknown-attributes) */
-__attribute__((optimize("-fno-strict-aliasing"))) /* See siphash_8b() */
+__attribute__((optimize("-fno-strict-aliasing"))) /* See csum_16b() */
uint16_t csum_unaligned(const void *buf, size_t len, uint32_t init)
{
return (uint16_t)~csum_fold(sum_16b(buf, len) + init);
@@ -247,7 +256,7 @@ void csum_icmp6(struct icmp6hdr *icmp6hr,
* - coding style adaptation
*/
/* NOLINTNEXTLINE(clang-diagnostic-unknown-attributes) */
-__attribute__((optimize("-fno-strict-aliasing"))) /* See siphash_8b() */
+__attribute__((optimize("-fno-strict-aliasing"))) /* See csum_16b() */
static uint32_t csum_avx2(const void *buf, size_t len, uint32_t init)
{
__m256i a, b, sum256, sum_a_hi, sum_a_lo, sum_b_hi, sum_b_lo, c, d;
@@ -395,7 +404,7 @@ less_than_128_bytes:
* Return: 16-bit folded, complemented checksum sum
*/
/* NOLINTNEXTLINE(clang-diagnostic-unknown-attributes) */
-__attribute__((optimize("-fno-strict-aliasing"))) /* See siphash_8b() */
+__attribute__((optimize("-fno-strict-aliasing"))) /* See csum_16b() */
uint16_t csum(const void *buf, size_t len, uint32_t init)
{
return (uint16_t)~csum_fold(csum_avx2(buf, len, init));
@@ -412,7 +421,7 @@ uint16_t csum(const void *buf, size_t len, uint32_t init)
* Return: 16-bit folded, complemented checksum
*/
/* NOLINTNEXTLINE(clang-diagnostic-unknown-attributes) */
-__attribute__((optimize("-fno-strict-aliasing"))) /* See siphash_8b() */
+__attribute__((optimize("-fno-strict-aliasing"))) /* See csum_16b() */
uint16_t csum(const void *buf, size_t len, uint32_t init)
{
return csum_unaligned(buf, len, init);