commit 451c5e02a847e4c98681457c7f9639492e0efd34
author Vitaly Buka <vitalybuka@google.com> Sun May 23 14:12:49 2021 -0700
committer Copybara-Service <copybara-worker@google.com> Tue May 25 19:11:26 2021 -0700
tree a65f91b533d3625eed32b85383e41edde1e4356a
parent 3b6a6d263f82f4ecd684b9c4edfa4d1964cec451

[NFC][scudo] Enforce header size alignment

As-is it should not change struct size, but it will
help to keep correct size if more fields added.

GitOrigin-RevId: 93d1e5822ed64abd777eb94ea9899e96c4c39fbe

secondary.h

diff --git a/secondary.h b/secondary.h
index ea5d680..77db873 100644
--- a/secondary.h
+++ b/secondary.h
@@ -28,7 +28,10 @@
 
 namespace LargeBlock {
 
-struct Header {
+struct alignas(Max<uptr>(archSupportsMemoryTagging()
+                             ? archMemoryTagGranuleSize()
+                             : 1,
+                         1U << SCUDO_MIN_ALIGNMENT_LOG)) Header {
   LargeBlock::Header *Prev;
   LargeBlock::Header *Next;
   uptr CommitBase;
@@ -38,9 +41,12 @@
   [[no_unique_address]] MapPlatformData Data;
 };
 
-constexpr uptr getHeaderSize() {
-  return roundUpTo(sizeof(Header), 1U << SCUDO_MIN_ALIGNMENT_LOG);
-}
+static_assert(sizeof(Header) % (1U << SCUDO_MIN_ALIGNMENT_LOG) == 0, "");
+static_assert(!archSupportsMemoryTagging() ||
+                  sizeof(Header) % archMemoryTagGranuleSize() == 0,
+              "");
+
+constexpr uptr getHeaderSize() { return sizeof(Header); }
 
 template <typename Config> static uptr addHeaderTag(uptr Ptr) {
   if (allocatorSupportsMemoryTagging<Config>())
@@ -49,8 +55,7 @@
 }
 
 template <typename Config> static Header *getHeader(uptr Ptr) {
-  return reinterpret_cast<Header *>(addHeaderTag<Config>(Ptr) -
-                                    getHeaderSize());
+  return reinterpret_cast<Header *>(addHeaderTag<Config>(Ptr)) - 1;
 }
 
 template <typename Config> static Header *getHeader(const void *Ptr) {