[llvm] r288096 - [asan/win] Align global registration metadata to its size

[Reid Kleckner via llvm-commits]

Author: rnk
Date: Mon Nov 28 19:32:21 2016
New Revision: 288096

URL: http://llvm.org/viewvc/llvm-project?rev=288096&view=rev
Log:
[asan/win] Align global registration metadata to its size

This way, when the linker adds padding between globals, we can skip over
the zero padding bytes and reliably find the start of the next metadata
global.

Modified:
    llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp
    llvm/trunk/test/Instrumentation/AddressSanitizer/global_metadata_windows.ll

Modified: llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp?rev=288096&r1=288095&r2=288096&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp (original)
+++ llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp Mon Nov 28 19:32:21 2016
@@ -1561,6 +1561,7 @@ bool AddressSanitizerModule::InstrumentG
   size_t n = GlobalsToChange.size();
   if (n == 0) return false;
 
+  auto &DL = M.getDataLayout();
   bool UseComdatMetadata = TargetTriple.isOSBinFormatCOFF();
   bool UseMachOGlobalsSection = ShouldUseMachOGlobalsSection();
   bool UseMetadataArray = !(UseComdatMetadata || UseMachOGlobalsSection);
@@ -1578,6 +1579,10 @@ bool AddressSanitizerModule::InstrumentG
   StructType *GlobalStructTy =
       StructType::get(IntptrTy, IntptrTy, IntptrTy, IntptrTy, IntptrTy,
                       IntptrTy, IntptrTy, IntptrTy, nullptr);
+  unsigned SizeOfGlobalStruct = DL.getTypeAllocSize(GlobalStructTy);
+  assert((isPowerOf2_32(SizeOfGlobalStruct) ||
+          !TargetTriple.isOSBinFormatCOFF()) &&
+         "global metadata will not be padded appropriately");
   SmallVector<Constant *, 16> Initializers(UseMetadataArray ? n : 0);
 
   // On recent Mach-O platforms, use a structure which binds the liveness of
@@ -1596,7 +1601,6 @@ bool AddressSanitizerModule::InstrumentG
   GlobalVariable *ModuleName = createPrivateGlobalForString(
       M, M.getModuleIdentifier(), /*AllowMerging*/ false);
 
-  auto &DL = M.getDataLayout();
   for (size_t i = 0; i < n; i++) {
     static const uint64_t kMaxGlobalRedzone = 1 << 18;
     GlobalVariable *G = GlobalsToChange[i];
@@ -1743,7 +1747,14 @@ bool AddressSanitizerModule::InstrumentG
         Initializer, Twine("__asan_global_") +
                              GlobalValue::getRealLinkageName(G->getName()));
     Metadata->setSection(getGlobalMetadataSection());
-    Metadata->setAlignment(1); // Don't leave padding in between.
+
+    // 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.
 
     // On platforms that support comdats, put the metadata and the
     // instrumented global in the same group. This ensures that the metadata

Modified: llvm/trunk/test/Instrumentation/AddressSanitizer/global_metadata_windows.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Instrumentation/AddressSanitizer/global_metadata_windows.ll?rev=288096&r1=288095&r2=288096&view=diff
==============================================================================
--- llvm/trunk/test/Instrumentation/AddressSanitizer/global_metadata_windows.ll (original)
+++ llvm/trunk/test/Instrumentation/AddressSanitizer/global_metadata_windows.ll Mon Nov 28 19:32:21 2016
@@ -13,7 +13,7 @@ $mystr = comdat any
 
 ; CHECK: $dead_global = comdat noduplicates
 ; CHECK: @dead_global = local_unnamed_addr global { i32, [60 x i8] } { i32 42, [60 x i8] zeroinitializer }, comdat, align 32
-; CHECK: @__asan_global_dead_global = internal global { {{.*}} }, section ".ASAN$GL", comdat($dead_global), align 1
+; CHECK: @__asan_global_dead_global = internal global { {{.*}} }, section ".ASAN$GL", comdat($dead_global), align 64
 
 @dead_global = local_unnamed_addr global i32 42, align 4
 @mystr = linkonce_odr unnamed_addr constant [5 x i8] c"main\00", comdat, align 1