[asan] Set alignment of __asan_global_* globals to sizeof(GlobalStruct)

When using profiling and ASan together (-fprofile-instr-generate -fcoverage-mapping -fsanitize=address), at least on Darwin, the section of globals that ASan emits (__asan_globals) is misaligned and starts at an odd offset. This really doesn't have anything to do with profiling, but it triggers the issue because profiling emits a string section, which can have arbitrary size.  This patch changes the alignment to sizeof(GlobalStruct).

Differential Revision: https://reviews.llvm.org/D28573



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@291715 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Instrumentation/AddressSanitizer.cpp

@@ -1598,8 +1598,7 @@ bool AddressSanitizerModule::InstrumentGlobals(IRBuilder<> &IRB, Module &M) {
       StructType::get(IntptrTy, IntptrTy, IntptrTy, IntptrTy, IntptrTy,
                       IntptrTy, IntptrTy, IntptrTy, nullptr);
   unsigned SizeOfGlobalStruct = DL.getTypeAllocSize(GlobalStructTy);
-  assert((isPowerOf2_32(SizeOfGlobalStruct) ||
-          !TargetTriple.isOSBinFormatCOFF()) &&
+  assert(isPowerOf2_32(SizeOfGlobalStruct) &&
          "global metadata will not be padded appropriately");
   SmallVector<Constant *, 16> Initializers(UseMetadataArray ? n : 0);
 
@@ -1766,13 +1765,11 @@ bool AddressSanitizerModule::InstrumentGlobals(IRBuilder<> &IRB, Module &M) {
                              GlobalValue::getRealLinkageName(G->getName()));
     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.
-    if (TargetTriple.isOSBinFormatCOFF())
-      Metadata->setAlignment(SizeOfGlobalStruct);
-    else
-      Metadata->setAlignment(1); // Don't leave padding in between.
+    Metadata->setAlignment(SizeOfGlobalStruct);
 
     // On platforms that support comdats, put the metadata and the
     // instrumented global in the same group. This ensures that the metadata

test/Instrumentation/AddressSanitizer/global_metadata_darwin.ll

@@ -16,7 +16,7 @@ target triple = "x86_64-apple-macosx10.11.0"
 
 
 ; Find the metadata for @global:
-; CHECK: [[METADATA:@.+]] = internal global {{.*}} @global {{.*}} section "__DATA,__asan_globals,regular", align 1
+; CHECK: [[METADATA:@.+]] = internal global {{.*}} @global {{.*}} section "__DATA,__asan_globals,regular", align 64
 
 ; Find the liveness binder for @global and its metadata:
 ; CHECK: @__asan_binder_global = internal global {{.*}} @global {{.*}} [[METADATA]] {{.*}} section "__DATA,__asan_liveness,regular,live_support"