[scudo] Small cleanup of memory tagging code.

[cferris1000]

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().

[llvmbot]

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: Christopher Ferris (cferris1000)

Changes

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().

---

Full diff: https://github.com/llvm/llvm-project/pull/166860.diff

5 Files Affected:

• (modified) compiler-rt/lib/scudo/standalone/combined.h (+1-2)
• (modified) compiler-rt/lib/scudo/standalone/memtag.h (+3-4)
• (modified) compiler-rt/lib/scudo/standalone/tests/memtag_test.cpp (-1)
• (modified) compiler-rt/lib/scudo/standalone/tests/secondary_test.cpp (+1-3)
• (modified) compiler-rt/lib/scudo/standalone/tests/wrappers_cpp_test.cpp (+1-2)

diff --git a/compiler-rt/lib/scudo/standalone/combined.h b/compiler-rt/lib/scudo/standalone/combined.h
index ffe9554203241..2d0f4f53d2ac5 100644
--- a/compiler-rt/lib/scudo/standalone/combined.h
+++ b/compiler-rt/lib/scudo/standalone/combined.h
@@ -171,8 +171,7 @@ class Allocator {
       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 83ebe676433eb..52897b3dca6ae 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 09093e11452dd..d0d93316f212e 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 855a3e6e6109f..8741c8299b57c 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 c802ed22fbad0..84359251a02aa 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;

[cferris1000]

Ping.

[vitalybuka]

Oh,
my thought during review: "nice! static locals are supported now" :)

https://lab.llvm.org/buildbot/#/builders/24/builds/14562

[vitalybuka]

CC @pcc

[pcc]

Memory tagging support status is deliberately cached in the UseMemoryTagging bit instead of here to avoid issues with static locals such as those pointed out by the buildbot.

[Prabhuk]

@cferris1000 -- We are starting to hit the same problems pointed out by @vitalybuka here https://lab.llvm.org/buildbot/#/builders/24/builds/14562 in our Google toolchain builders as well.

[cferris1000]

Let me revert this and I'll fix this.