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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 993bdb9 and ad2ad69, 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
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src/include/c.h

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#define pg_attribute_unused()
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#endif
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/*
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* Place this macro before functions that should be allowed to make misaligned
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* accesses. Think twice before using it on non-x86-specific code!
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* Testing can be done with "-fsanitize=alignment -fsanitize-trap=alignment"
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* on clang, or "-fsanitize=alignment -fno-sanitize-recover=alignment" on gcc.
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*/
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#if __clang_major__ >= 7 || __GNUC__ >= 8
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#define pg_attribute_no_sanitize_alignment() __attribute__((no_sanitize("alignment")))
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#else
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#define pg_attribute_no_sanitize_alignment()
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#endif
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/*
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* Append PG_USED_FOR_ASSERTS_ONLY to definitions of variables that are only
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* used in assert-enabled builds, to avoid compiler warnings about unused

src/port/pg_crc32c_sse42.c

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#include <nmmintrin.h>
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pg_attribute_no_sanitize_alignment()
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pg_crc32c
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pg_comp_crc32c_sse42(pg_crc32c crc, const void *data, size_t len)
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{

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