[compiler-rt] b27749d - [scudo] Small cleanup of memory tagging code part 2. (#168807)

[via llvm-commits]

Author: Christopher Ferris
Date: 2025-11-21T09:08:31-08:00
New Revision: b27749d8c7191f894e337a402344af7a9de9a5b0

URL: https://github.com/llvm/llvm-project/commit/b27749d8c7191f894e337a402344af7a9de9a5b0
DIFF: https://github.com/llvm/llvm-project/commit/b27749d8c7191f894e337a402344af7a9de9a5b0.diff

LOG: [scudo] Small cleanup of memory tagging code part 2. (#168807)

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 the function.

Modify iterateOverChunks() to call useMemoryTagging<>(Options) to
determine if mte is supported. This already uses the cached check of
systemSupportsMemoryTagging() rather than directly calling that
function.

Updated the code that calls systemSupportsMemoryTagging().

Added: 
    

Modified: 
    compiler-rt/lib/scudo/standalone/combined.h
    compiler-rt/lib/scudo/standalone/memtag.h
    compiler-rt/lib/scudo/standalone/tests/memtag_test.cpp
    compiler-rt/lib/scudo/standalone/tests/secondary_test.cpp

Removed: 
    


################################################################################
diff  --git a/compiler-rt/lib/scudo/standalone/combined.h b/compiler-rt/lib/scudo/standalone/combined.h
index ffe9554203241..5108f02f2dcbb 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 =
@@ -689,16 +688,15 @@ class Allocator {
       Base = untagPointer(Base);
     const uptr From = Base;
     const uptr To = Base + Size;
-    bool MayHaveTaggedPrimary =
-        allocatorSupportsMemoryTagging<AllocatorConfig>() &&
-        systemSupportsMemoryTagging();
+    const Options Options = Primary.Options.load();
+    bool MayHaveTaggedPrimary = useMemoryTagging<AllocatorConfig>(Options);
     auto Lambda = [this, From, To, MayHaveTaggedPrimary, Callback,
                    Arg](uptr Block) {
       if (Block < From || Block >= To)
         return;
       uptr Chunk;
       Chunk::UnpackedHeader Header;
-      if (MayHaveTaggedPrimary) {
+      if (UNLIKELY(MayHaveTaggedPrimary)) {
         // A chunk header can either have a zero tag (tagged primary) or the
         // header tag (secondary, or untagged primary). We don't know which so
         // try both.

diff  --git a/compiler-rt/lib/scudo/standalone/memtag.h b/compiler-rt/lib/scudo/standalone/memtag.h
index 83ebe676433eb..073e72c46f68a 100644
--- a/compiler-rt/lib/scudo/standalone/memtag.h
+++ b/compiler-rt/lib/scudo/standalone/memtag.h
@@ -108,7 +108,7 @@ inline void enableSystemMemoryTaggingTestOnly() {
 
 #else // !SCUDO_CAN_USE_MTE
 
-inline bool systemSupportsMemoryTagging() { return false; }
+inline constexpr bool systemSupportsMemoryTagging() { return false; }
 
 inline NORETURN bool systemDetectsMemoryTagFaultsTestOnly() {
   UNREACHABLE("memory tagging not supported");
@@ -261,9 +261,7 @@ inline uptr loadTag(uptr Ptr) {
 
 #else
 
-inline NORETURN bool systemSupportsMemoryTagging() {
-  UNREACHABLE("memory tagging not supported");
-}
+inline constexpr 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);