add some assertions

Author: Camsyn

compiler-rt/lib/tsan/rtl/tsan_rtl.cpp

@@ -582,6 +582,16 @@ void UnmapShadow(ThreadState* thr, uptr addr, uptr size) {
 #endif
 
 void MapShadow(uptr addr, uptr size) {
+  // Although named MapShadow, this function's semantic is unrelated to
+  // UnmapShadow. This function currently only used for Go's lazy allocation
+  // of shadow, whose targets are program section (e.g., bss, data, etc.).
+  // Therefore, we can guarantee that the addr and size align to kShadowCell
+  // and kMetaShadowCell by the following assertions.
+  DCHECK_EQ(addr % kShadowCell, 0);
+  DCHECK_EQ(size % kShadowCell, 0);
+  DCHECK_EQ(addr % kMetaShadowCell, 0);
+  DCHECK_EQ(size % kMetaShadowCell, 0);
+
   // Ensure thead registry lock held, so as to synchronize
   // with DoReset, which also access the mapped_shadow_* ctxt fields.
   ThreadRegistryLock lock0(&ctx->thread_registry);

compiler-rt/lib/tsan/rtl/tsan_sync.cpp

@@ -246,6 +246,20 @@ void MetaMap::MoveMemory(uptr src, uptr dst, uptr sz) {
   // there are no concurrent accesses to the regions (e.g. stop-the-world).
   CHECK_NE(src, dst);
   CHECK_NE(sz, 0);
+
+  // The current MoveMemory implementation behaves incorrectly when src, dst,
+  // and sz are not aligned to kMetaShadowCell.
+  // For example, with kMetaShadowCell == 8:
+  // - src = 4: unexpectedly clears the metadata for the range [0, 4).
+  // - src = 16, dst = 4, size = 8: A sync variable for addr = 20, which should
+  //   be moved to the metadata for address 8, is incorrectly moved to the
+  //   metadata for address 0 instead.
+  // - src = 0, sz = 4: fails to move the tail metadata.
+  // Therefore, the following assertions is needed.
+  DCHECK_EQ(src % kMetaShadowCell, 0);
+  DCHECK_EQ(dst % kMetaShadowCell, 0);
+  DCHECK_EQ(sz % kMetaShadowCell, 0);
+
   uptr diff = dst - src;
   u32 *src_meta, *dst_meta, *src_meta_end;
   uptr inc;