From 22001684623bd95b4e1d5c21854f222a37b13267 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Sat, 13 Feb 2021 17:49:08 -0500 Subject: [PATCH] pg_attribute_no_sanitize_alignment() macro Modern gcc and clang compilers offer alignment sanitizers, which help to detect pointer misalignment. However, our codebase already contains x86-specific crc32 computation code, which uses unalignment access. Thankfully, those compilers also support the attribute, which disables alignment sanitizers at the function level. This commit adds pg_attribute_no_sanitize_alignment(), which wraps this attribute, and applies it to pg_comp_crc32c_sse42() function. Back-patch of commits 993bdb9f9 and ad2ad698a, to enable doing alignment testing in all supported branches. Discussion: https://postgr.es/m/CAPpHfdsne3%3DT%3DfMNU45PtxdhSL_J2PjLTeS8rwKnJzUR4YNd4w%40mail.gmail.com Discussion: https://postgr.es/m/475514.1612745257%40sss.pgh.pa.us Author: Alexander Korotkov, revised by Tom Lane Reviewed-by: Tom Lane --- src/include/c.h | 12 ++++++++++++ src/port/pg_crc32c_sse42.c | 1 + 2 files changed, 13 insertions(+) diff --git a/src/include/c.h b/src/include/c.h index 24699ae291..b21f9643a6 100644 --- a/src/include/c.h +++ b/src/include/c.h @@ -112,6 +112,18 @@ #define pg_attribute_unused() #endif +/* + * Place this macro before functions that should be allowed to make misaligned + * accesses. Think twice before using it on non-x86-specific code! + * Testing can be done with "-fsanitize=alignment -fsanitize-trap=alignment" + * on clang, or "-fsanitize=alignment -fno-sanitize-recover=alignment" on gcc. + */ +#if __clang_major__ >= 7 || __GNUC__ >= 8 +#define pg_attribute_no_sanitize_alignment() __attribute__((no_sanitize("alignment"))) +#else +#define pg_attribute_no_sanitize_alignment() +#endif + /* * Append PG_USED_FOR_ASSERTS_ONLY to definitions of variables that are only * used in assert-enabled builds, to avoid compiler warnings about unused diff --git a/src/port/pg_crc32c_sse42.c b/src/port/pg_crc32c_sse42.c index b9def7e2ea..fb2b54fa46 100644 --- a/src/port/pg_crc32c_sse42.c +++ b/src/port/pg_crc32c_sse42.c @@ -18,6 +18,7 @@ #include +pg_attribute_no_sanitize_alignment() pg_crc32c pg_comp_crc32c_sse42(pg_crc32c crc, const void *data, size_t len) {