From 04b10a8d907d8ceb09e3adb4885c02f546841bbc Mon Sep 17 00:00:00 2001 From: David Gibson Date: Thu, 28 Sep 2023 11:21:01 +1000 Subject: siphash, checksum: Move TBAA explanation to checksum.c A number of checksum and hash functions require workarounds for the odd behaviour of Type-Baased Alias Analysis. We have a detailed comment about this on siphash_8b() and other functions reference that. Move the main comment to csume_16b() instead, because we're going to reorganise things in siphash.c. Signed-off-by: David Gibson Signed-off-by: Stefano Brivio --- siphash.c | 19 +++++-------------- 1 file changed, 5 insertions(+), 14 deletions(-) (limited to 'siphash.c') diff --git a/siphash.c b/siphash.c index 91bcc5d..d2b068c 100644 --- a/siphash.c +++ b/siphash.c @@ -24,17 +24,8 @@ * * Return: the 64-bit hash output */ -/* 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"))) +__attribute__((optimize("-fno-strict-aliasing"))) /* See csum_16b() */ /* cppcheck-suppress unusedFunction */ uint64_t siphash_8b(const uint8_t *in, const uint64_t *k) { @@ -53,7 +44,7 @@ uint64_t siphash_8b(const uint8_t *in, const uint64_t *k) * Return: the 64-bit hash output */ /* NOLINTNEXTLINE(clang-diagnostic-unknown-attributes) */ -__attribute__((optimize("-fno-strict-aliasing"))) /* See siphash_8b() */ +__attribute__((optimize("-fno-strict-aliasing"))) /* See csum_16b() */ /* cppcheck-suppress unusedFunction */ uint64_t siphash_12b(const uint8_t *in, const uint64_t *k) { @@ -73,7 +64,7 @@ uint64_t siphash_12b(const uint8_t *in, const uint64_t *k) * Return: the 64-bit hash output */ /* NOLINTNEXTLINE(clang-diagnostic-unknown-attributes) */ -__attribute__((optimize("-fno-strict-aliasing"))) /* See siphash_8b() */ +__attribute__((optimize("-fno-strict-aliasing"))) /* See csum_16b() */ uint64_t siphash_20b(const uint8_t *in, const uint64_t *k) { struct siphash_state state = SIPHASH_INIT(k); @@ -94,7 +85,7 @@ uint64_t siphash_20b(const uint8_t *in, const uint64_t *k) * Return: the 64-bit hash output */ /* NOLINTNEXTLINE(clang-diagnostic-unknown-attributes) */ -__attribute__((optimize("-fno-strict-aliasing"))) /* See siphash_8b() */ +__attribute__((optimize("-fno-strict-aliasing"))) /* See csum_16b() */ /* cppcheck-suppress unusedFunction */ uint64_t siphash_32b(const uint8_t *in, const uint64_t *k) { @@ -116,7 +107,7 @@ uint64_t siphash_32b(const uint8_t *in, const uint64_t *k) * Return: the 64-bit hash output */ /* NOLINTNEXTLINE(clang-diagnostic-unknown-attributes) */ -__attribute__((optimize("-fno-strict-aliasing"))) /* See siphash_8b() */ +__attribute__((optimize("-fno-strict-aliasing"))) /* See csum_16b() */ uint64_t siphash_36b(const uint8_t *in, const uint64_t *k) { struct siphash_state state = SIPHASH_INIT(k); -- cgit v1.2.3