From 046ae855360614c5980d0ced0c55b5de507bd9ad Mon Sep 17 00:00:00 2001
From: Christopher Ferris <cferris1000@users.noreply.github.com>
Date: Mon, 10 Nov 2025 14:17:23 -0800
Subject: [PATCH] [scudo] Small cleanup of memory tagging code. (#166860)

Make the systemSupportsMemoryTagging() function return even on system
that don't support memory tagging. This avoids the need to always check
if memory tagging is supported before calling th function.

Make systemSupportsMemoryTagging() cache the getauxval return value
instead of calling the function every time.

Updated the code that calls systemSupportsMemoryTagging().
---
 compiler-rt/lib/scudo/standalone/combined.h                | 3 +--
 compiler-rt/lib/scudo/standalone/memtag.h                  | 7 +++----
 compiler-rt/lib/scudo/standalone/tests/memtag_test.cpp     | 1 -
 compiler-rt/lib/scudo/standalone/tests/secondary_test.cpp  | 4 +---
 .../lib/scudo/standalone/tests/wrappers_cpp_test.cpp       | 3 +--
 5 files changed, 6 insertions(+), 12 deletions(-)

diff --git a/compiler-rt/lib/scudo/standalone/combined.h b/compiler-rt/lib/scudo/standalone/combined.h
index ffe955420324..2d0f4f53d2ac 100644
--- a/compiler-rt/lib/scudo/standalone/combined.h
+++ b/compiler-rt/lib/scudo/standalone/combined.h
@@ -171,8 +171,7 @@ public:
       Primary.Options.set(OptionBit::DeallocTypeMismatch);
     if (getFlags()->delete_size_mismatch)
       Primary.Options.set(OptionBit::DeleteSizeMismatch);
-    if (allocatorSupportsMemoryTagging<AllocatorConfig>() &&
-        systemSupportsMemoryTagging())
+    if (systemSupportsMemoryTagging())
       Primary.Options.set(OptionBit::UseMemoryTagging);
 
     QuarantineMaxChunkSize =
diff --git a/compiler-rt/lib/scudo/standalone/memtag.h b/compiler-rt/lib/scudo/standalone/memtag.h
index 83ebe676433e..52897b3dca6a 100644
--- a/compiler-rt/lib/scudo/standalone/memtag.h
+++ b/compiler-rt/lib/scudo/standalone/memtag.h
@@ -66,7 +66,8 @@ inline bool systemSupportsMemoryTagging() {
 #ifndef HWCAP2_MTE
 #define HWCAP2_MTE (1 << 18)
 #endif
-  return getauxval(AT_HWCAP2) & HWCAP2_MTE;
+  static bool SupportsMemoryTagging = getauxval(AT_HWCAP2) & HWCAP2_MTE;
+  return SupportsMemoryTagging;
 }
 
 inline bool systemDetectsMemoryTagFaultsTestOnly() {
@@ -261,9 +262,7 @@ inline uptr loadTag(uptr Ptr) {
 
 #else
 
-inline NORETURN bool systemSupportsMemoryTagging() {
-  UNREACHABLE("memory tagging not supported");
-}
+inline bool systemSupportsMemoryTagging() { return false; }
 
 inline NORETURN bool systemDetectsMemoryTagFaultsTestOnly() {
   UNREACHABLE("memory tagging not supported");
diff --git a/compiler-rt/lib/scudo/standalone/tests/memtag_test.cpp b/compiler-rt/lib/scudo/standalone/tests/memtag_test.cpp
index 09093e11452d..d0d93316f212 100644
--- a/compiler-rt/lib/scudo/standalone/tests/memtag_test.cpp
+++ b/compiler-rt/lib/scudo/standalone/tests/memtag_test.cpp
@@ -28,7 +28,6 @@ TEST(MemtagBasicDeathTest, Unsupported) {
   EXPECT_DEATH(untagPointer((uptr)0), "not supported");
   EXPECT_DEATH(extractTag((uptr)0), "not supported");
 
-  EXPECT_DEATH(systemSupportsMemoryTagging(), "not supported");
   EXPECT_DEATH(systemDetectsMemoryTagFaultsTestOnly(), "not supported");
   EXPECT_DEATH(enableSystemMemoryTaggingTestOnly(), "not supported");
 
diff --git a/compiler-rt/lib/scudo/standalone/tests/secondary_test.cpp b/compiler-rt/lib/scudo/standalone/tests/secondary_test.cpp
index 855a3e6e6109..8741c8299b57 100644
--- a/compiler-rt/lib/scudo/standalone/tests/secondary_test.cpp
+++ b/compiler-rt/lib/scudo/standalone/tests/secondary_test.cpp
@@ -27,9 +27,7 @@
 const scudo::uptr PageSize = scudo::getPageSizeCached();
 
 template <typename Config> static scudo::Options getOptionsForConfig() {
-  if (!Config::getMaySupportMemoryTagging() ||
-      !scudo::archSupportsMemoryTagging() ||
-      !scudo::systemSupportsMemoryTagging())
+  if (!scudo::systemSupportsMemoryTagging())
     return {};
   scudo::AtomicOptions AO;
   AO.set(scudo::OptionBit::UseMemoryTagging);
diff --git a/compiler-rt/lib/scudo/standalone/tests/wrappers_cpp_test.cpp b/compiler-rt/lib/scudo/standalone/tests/wrappers_cpp_test.cpp
index c802ed22fbad..84359251a02a 100644
--- a/compiler-rt/lib/scudo/standalone/tests/wrappers_cpp_test.cpp
+++ b/compiler-rt/lib/scudo/standalone/tests/wrappers_cpp_test.cpp
@@ -187,8 +187,7 @@ TEST_F(ScudoWrappersCppTest, ThreadedNew) {
   // TODO: Investigate why libc sometimes crashes with tag missmatch in
   // __pthread_clockjoin_ex.
   std::unique_ptr<scudo::ScopedDisableMemoryTagChecks> NoTags;
-  if (!SCUDO_ANDROID && scudo::archSupportsMemoryTagging() &&
-      scudo::systemSupportsMemoryTagging())
+  if (!SCUDO_ANDROID && scudo::systemSupportsMemoryTagging())
     NoTags = std::make_unique<scudo::ScopedDisableMemoryTagChecks>();
 
   Ready = false;