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pg_attribute_no_sanitize_alignment() macro

Modern gcc and clang compilers offer alignment sanitizers, which help to detectpointer misalignment. However, our codebase already contains x86-specificcrc32 computation code, which uses unalignment access. Thankfully, thosecompilers also support the attribute, which disables alignment sanitizers atthe 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 commits993bdb9 andad2ad69, to enable doingalignment testing in all supported branches.Discussion:https://postgr.es/m/CAPpHfdsne3%3DT%3DfMNU45PtxdhSL_J2PjLTeS8rwKnJzUR4YNd4w%40mail.gmail.comDiscussion:https://postgr.es/m/475514.1612745257%40sss.pgh.pa.usAuthor: Alexander Korotkov, revised by Tom LaneReviewed-by: Tom Lane

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src
- include
  - c.h
- port
  - pg_crc32c_sse42.c

2 files changed

+13

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lines changed

`‎src/include/c.h`

Lines changed: 12 additions & 0 deletions

Original file line number	Diff line number	Diff line change
`@@ -112,6 +112,18 @@`
`112`	`112`	`#definepg_attribute_unused()`
`113`	`113`	`#endif`
`114`	`114`
	`115`	`+/*`
	`116`	`+ * Place this macro before functions that should be allowed to make misaligned`
	`117`	`+ * accesses. Think twice before using it on non-x86-specific code!`
	`118`	`+ * Testing can be done with "-fsanitize=alignment -fsanitize-trap=alignment"`
	`119`	`+ * on clang, or "-fsanitize=alignment -fno-sanitize-recover=alignment" on gcc.`
	`120`	`+ */`
	`121`	`+#if__clang_major__ >=7\|\|__GNUC__ >=8`
	`122`	`+#definepg_attribute_no_sanitize_alignment() __attribute__((no_sanitize("alignment")))`
	`123`	`+#else`
	`124`	`+#definepg_attribute_no_sanitize_alignment()`
	`125`	`+#endif`
	`126`	`+`
`115`	`127`	`/*`
`116`	`128`	`* Append PG_USED_FOR_ASSERTS_ONLY to definitions of variables that are only`
`117`	`129`	`* used in assert-enabled builds, to avoid compiler warnings about unused`

`‎src/port/pg_crc32c_sse42.c`

Lines changed: 1 addition & 0 deletions

Original file line number	Diff line number	Diff line change
`@@ -18,6 +18,7 @@`
`18`	`18`
`19`	`19`	`#include<nmmintrin.h>`
`20`	`20`
	`21`	`+pg_attribute_no_sanitize_alignment()`
`21`	`22`	`pg_crc32c`
`22`	`23`	`pg_comp_crc32c_sse42(pg_crc32ccrc,constvoid*data,size_tlen)`
`23`	`24`	`{`

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Commitc3dc311

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`‎src/include/c.h`

`‎src/port/pg_crc32c_sse42.c`

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