fix alignment of guard blocks (KhronosGroup#4137)

Author: jamesdolan

glslang/Include/PoolAlloc.h

@@ -84,9 +84,9 @@ class TAllocation {
         // makes the compiler print warnings about 0 length memsets,
         // even with the if() protecting them.
 #       ifdef GUARD_BLOCKS
-            memset(preGuard(),  guardBlockBeginVal, guardBlockSize);
+            memset(preGuard(),  guardBlockBeginVal, guardBlockSize());
             memset(data(),      userDataFill,       size);
-            memset(postGuard(), guardBlockEndVal,   guardBlockSize);
+            memset(postGuard(), guardBlockEndVal,   guardBlockSize());
 #       endif
     }
 
@@ -100,20 +100,20 @@ class TAllocation {
     // Return total size needed to accommodate user buffer of 'size',
     // plus our tracking data.
     inline static size_t allocationSize(size_t size) {
-        return size + 2 * guardBlockSize + headerSize();
+        return size + 2 * guardBlockSize() + headerSize();
     }
 
     // Offset from surrounding buffer to get to user data buffer.
     inline static unsigned char* offsetAllocation(unsigned char* m) {
-        return m + guardBlockSize + headerSize();
+        return m + guardBlockSize() + headerSize();
     }
 
 private:
     void checkGuardBlock(unsigned char* blockMem, unsigned char val, const char* locText) const;
 
     // Find offsets to pre and post guard blocks, and user data buffer
     unsigned char* preGuard()  const { return mem + headerSize(); }
-    unsigned char* data()      const { return preGuard() + guardBlockSize; }
+    unsigned char* data()      const { return preGuard() + guardBlockSize(); }
     unsigned char* postGuard() const { return data() + size; }
 
     size_t size;                  // size of the user data area
@@ -125,15 +125,19 @@ class TAllocation {
     static inline constexpr unsigned char userDataFill = 0xcd;
 
 #   ifdef GUARD_BLOCKS
-    static inline constexpr size_t guardBlockSize = 16;
-#   else
-    static inline constexpr size_t guardBlockSize = 0;
-#   endif
-
-#   ifdef GUARD_BLOCKS
-    inline static size_t headerSize() { return sizeof(TAllocation); }
+    inline static constexpr size_t headerSize() { return sizeof(TAllocation); }
+    inline static constexpr size_t guardBlockSize() {
+        constexpr size_t minGuardSize = 16;
+        constexpr size_t alignmentSize = 16;
+        constexpr size_t guardLayoutSize =
+            (minGuardSize + sizeof(TAllocation) + alignmentSize - 1) & ~(alignmentSize - 1);
+        static_assert((guardLayoutSize % alignmentSize) == 0,
+                      "Guard block layout is not 16-byte aligned.");
+        return guardLayoutSize - sizeof(TAllocation);
+    }
 #   else
-    inline static size_t headerSize() { return 0; }
+    inline static constexpr size_t headerSize() { return 0; }
+    inline static constexpr size_t guardBlockSize() { return 0; }
 #   endif
 };
 

glslang/MachineIndependent/PoolAlloc.cpp

@@ -148,7 +148,7 @@ void TAllocation::checkGuardBlock(unsigned char*, unsigned char, const char*) co
 #endif
 {
 #ifdef GUARD_BLOCKS
-    for (size_t x = 0; x < guardBlockSize; x++) {
+    for (size_t x = 0; x < guardBlockSize(); x++) {
         if (blockMem[x] != val) {
             const int maxSize = 80;
             char assertMsg[maxSize];
@@ -160,7 +160,7 @@ void TAllocation::checkGuardBlock(unsigned char*, unsigned char, const char*) co
         }
     }
 #else
-    assert(guardBlockSize == 0);
+    assert(guardBlockSize() == 0);
 #endif
 }