v20-0001-Add-macro-to-disable-address-safety-instrumentat.patch

From 29fbfedd806030a14d817132d29d6755e32daec7 Mon Sep 17 00:00:00 2001
From: John Naylor <john.naylor@postgresql.org>
Date: Fri, 22 Mar 2024 13:01:33 +0700
Subject: [PATCH v20 1/3] Add macro to disable address safety instrumentation

fasthash_accum_cstring_aligned() uses a technique, found in various
strlen() implementations, to detect a string's NUL terminator by
reading a word at at time. That triggers failures when testing with
"-fsanitize=address", at least with frontend code. To enable using
this function anywhere, add a function attribute macro to disable
such testing.

Reviewed by

Discussion: https://postgr.es/m/CANWCAZbwvp7oUEkbw-xP4L0_S_WNKq-J-ucP4RCNDPJnrakUPw%40mail.gmail.com
---
 src/include/c.h                      | 13 +++++++++++++
 src/include/common/hashfn_unstable.h |  5 ++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/src/include/c.h b/src/include/c.h
index cf37e02fe1..dc1841346c 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -135,6 +135,19 @@
 #define pg_nodiscard
 #endif
 
+/*
+ * This macro will disable address safety instrumentation for a function
+ * when running with "-fsanitize=address". Think twice before using this!
+ */
+#if defined(__clang__) || __GNUC__ >= 8
+#define pg_attribute_no_sanitize_address() __attribute__((no_sanitize("address")))
+#elif __has_attribute(no_sanitize_address)
+/* This would work for clang, but it's deprecated. */
+#define pg_attribute_no_sanitize_address() __attribute__((no_sanitize_address))
+#else
+#define pg_attribute_no_sanitize_address()
+#endif
+
 /*
  * Place this macro before functions that should be allowed to make misaligned
  * accesses.  Think twice before using it on non-x86-specific code!
diff --git a/src/include/common/hashfn_unstable.h b/src/include/common/hashfn_unstable.h
index 791750d136..4227afd141 100644
--- a/src/include/common/hashfn_unstable.h
+++ b/src/include/common/hashfn_unstable.h
@@ -213,8 +213,11 @@ fasthash_accum_cstring_unaligned(fasthash_state *hs, const char *str)
  *
  * With an aligned pointer, we consume the string a word at a time.
  * Loading the word containing the NUL terminator cannot segfault since
- * allocation boundaries are suitably aligned.
+ * allocation boundaries are suitably aligned. To keep from setting
+ * off alarms with address sanitizers, exclude this function from
+ * such testing.
  */
+pg_attribute_no_sanitize_address()
 static inline size_t
 fasthash_accum_cstring_aligned(fasthash_state *hs, const char *str)
 {
-- 
2.44.0