pg_attribute_no_sanitize_alignment() macro

akorotkov · akorotkov · commit 993bdb9f935a · 2021-02-12T17:23:35.000+03:00
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. 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
diff --git a/src/include/c.h b/src/include/c.h
@@ -132,6 +132,18 @@
 #define pg_nodiscard
 #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__ >= 5
+#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
@@ -18,6 +18,7 @@
 
 #include "port/pg_crc32c.h"
 
+pg_attribute_no_sanitize_alignment()
 pg_crc32c
 pg_comp_crc32c_sse42(pg_crc32c crc, const void *data, size_t len)
 {

Original file line number	Diff line number	Diff line change
`@@ -18,6 +18,7 @@`
`18`	`18`
`19`	`19`	`#include "port/pg_crc32c.h"`
`20`	`20`
	`21`	`+pg_attribute_no_sanitize_alignment()`
`21`	`22`	`pg_crc32c`
`22`	`23`	`pg_comp_crc32c_sse42(pg_crc32c crc, const void *data, size_t len)`
`23`	`24`	`{`