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commit    993bdb9f935a751935a03c80d30857150ba2b645
Author:   Alexander Korotkov <akorotkov@postgresql.org>
Date:     Fri Feb 12 14:14:33 2021 +0000
First released in: 14.0

    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.
    
    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 ae978830daf..a86342093eb 100644
--- 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
index 3b94a7388ab..10fc01e1f06 100644
--- 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)
 {


[parent: c8b21b037814]