[asan] Don't overalign global metadata.

[eugenis]

Summary

Other than on COFF with incremental linking, global metadata should not need any extra alignment.

[pcc]

lib/Transforms/Instrumentation/AddressSanitizer.cpp

1618–1621

Move to InstrumentGlobalsCOFF?

[eugenis]

lib/Transforms/Instrumentation/AddressSanitizer.cpp

1618–1621

of course!

[pcc]

LGTM

lib/Transforms/Instrumentation/AddressSanitizer.cpp

void AddressSanitizerModule::SetComdatForGlobalMetadata(
   Metadata->setComdat(G->getComdat());
 }
 
 // Create a separate metadata global and put it in the appropriate ASan
 // global registration section.
 GlobalVariable *
 AddressSanitizerModule::CreateMetadataGlobal(Module &M, Constant *Initializer,
                                              StringRef OriginalName) {
-  auto &DL = M.getDataLayout();
   GlobalVariable *Metadata =
       new GlobalVariable(M, Initializer->getType(), false,
                          GlobalVariable::InternalLinkage, Initializer,
                          Twine("__asan_global_") +
                              GlobalValue::getRealLinkageName(OriginalName));
   Metadata->setSection(getGlobalMetadataSection());
-
-  // We don't want any padding, but we also need a reasonable alignment.
-  // The MSVC linker always inserts padding when linking incrementally. We
-  // cope with that by aligning each struct to its size, which must be a power
-  // of two.
-  unsigned SizeOfGlobalStruct = DL.getTypeAllocSize(Initializer->getType());
-  assert(isPowerOf2_32(SizeOfGlobalStruct) &&
-         "global metadata will not be padded appropriately");
-  Metadata->setAlignment(SizeOfGlobalStruct);
   return Metadata;
 }
 
 IRBuilder<> AddressSanitizerModule::CreateAsanModuleDtor(Module &M) {
   Function *AsanDtorFunction =
       Function::Create(FunctionType::get(Type::getVoidTy(*C), false),
                        GlobalValue::InternalLinkage, kAsanModuleDtorName, &M);
   BasicBlock *AsanDtorBB = BasicBlock::Create(*C, "", AsanDtorFunction);
   appendToGlobalDtors(M, AsanDtorFunction, kAsanCtorAndDtorPriority);
 
   return IRBuilder<>(ReturnInst::Create(*C, AsanDtorBB));
 }
 
 void AddressSanitizerModule::InstrumentGlobalsCOFF(
     IRBuilder<> &IRB, Module &M, ArrayRef<GlobalVariable *> ExtendedGlobals,
     ArrayRef<Constant *> MetadataInitializers) {
   assert(ExtendedGlobals.size() == MetadataInitializers.size());
+  auto &DL = M.getDataLayout();
 
   for (size_t i = 0; i < ExtendedGlobals.size(); i++) {
+    Constant *Initializer = MetadataInitializers[i];
     GlobalVariable *G = ExtendedGlobals[i];
     GlobalVariable *Metadata =
-        CreateMetadataGlobal(M, MetadataInitializers[i], G->getName());
+        CreateMetadataGlobal(M, Initializer, G->getName());
+
+    // The MSVC linker always inserts padding when linking incrementally. We
+    // cope with that by aligning each struct to its size, which must be a power
+    // of two.
+    unsigned SizeOfGlobalStruct = DL.getTypeAllocSize(Initializer->getType());
+    assert(isPowerOf2_32(SizeOfGlobalStruct) &&
+           "global metadata will not be padded appropriately");
+    Metadata->setAlignment(SizeOfGlobalStruct);
+
     SetComdatForGlobalMetadata(G, Metadata);
   }
 }
 
 void AddressSanitizerModule::InstrumentGlobalsMachO(
     IRBuilder<> &IRB, Module &M, ArrayRef<GlobalVariable *> ExtendedGlobals,
     ArrayRef<Constant *> MetadataInitializers) {
   assert(ExtendedGlobals.size() == MetadataInitializers.size());

test/Instrumentation/AddressSanitizer/global_metadata_darwin.ll

 
 !llvm.asan.globals = !{!0}
 
 !0 = !{[1 x i32]* @global, !1, !"global", i1 false, i1 false}
 !1 = !{!"test-globals.c", i32 1, i32 5}
 
 
 ; Find the metadata for @global:
-; CHECK: [[METADATA:@.+]] = internal global {{.*}} @global {{.*}} section "__DATA,__asan_globals,regular", align 64
+; CHECK: [[METADATA:@.+]] = internal global {{.*}} @global {{.*}} section "__DATA,__asan_globals,regular"
 
 ; Find the liveness binder for @global and its metadata:
 ; CHECK: @__asan_binder_global = internal global {{.*}} @global {{.*}} [[METADATA]] {{.*}} section "__DATA,__asan_liveness,regular,live_support"
 
 ; The binder has to be inserted to llvm.compiler.used to avoid being stripped
 ; during LTO.
 ; CHECK: @llvm.compiler.used {{.*}} @__asan_binder_global {{.*}} section "llvm.metadata"