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| author | David Gibson <david@gibson.dropbear.id.au> | 2023-09-28 11:21:01 +1000 |
|---|---|---|
| committer | Stefano Brivio <sbrivio@redhat.com> | 2023-09-30 12:40:51 +0200 |
| commit | 04b10a8d907d8ceb09e3adb4885c02f546841bbc (patch) | |
| tree | 4b2b473f9f690165a1b40d10d9d99248c5bdc3ba /siphash.c | |
| parent | ceae8422c1ca997b80436e9b574f48146e92d12c (diff) | |
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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 <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Diffstat (limited to 'siphash.c')
| -rw-r--r-- | siphash.c | 19 |
1 files changed, 5 insertions, 14 deletions
@@ -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); |