From 189c55251849076e17ddab590c1302f4af0e60f8 Mon Sep 17 00:00:00 2001
From: Leonard Chan <leonardchan@google.com>
Date: Fri, 9 Jul 2021 13:41:48 -0700
Subject: [PATCH] [compiler-rt][hwasan] Refactor kAliasRegionStart usage

This moves logic for setting kAliasRegionStart into hwasan_allocator.cpp
so other platforms that do not support aliasing mode will not need to define
kAliasRegionStart.

Differential Revision: https://reviews.llvm.org/D105725
---
 compiler-rt/lib/hwasan/hwasan_allocator.cpp | 19 ++++++++++++++++++-
 compiler-rt/lib/hwasan/hwasan_linux.cpp     | 14 --------------
 compiler-rt/lib/hwasan/hwasan_mapping.h     |  4 ++--
 3 files changed, 20 insertions(+), 17 deletions(-)

diff --git a/compiler-rt/lib/hwasan/hwasan_allocator.cpp b/compiler-rt/lib/hwasan/hwasan_allocator.cpp
index e53de53..ef6d4d6 100644
--- a/compiler-rt/lib/hwasan/hwasan_allocator.cpp
+++ b/compiler-rt/lib/hwasan/hwasan_allocator.cpp
@@ -80,12 +80,29 @@ void GetAllocatorStats(AllocatorStatCounters s) {
   allocator.GetStats(s);
 }
 
+uptr GetAliasRegionStart() {
+#if defined(HWASAN_ALIASING_MODE)
+  constexpr uptr kAliasRegionOffset = 1ULL << (kTaggableRegionCheckShift - 1);
+  uptr AliasRegionStart =
+      __hwasan_shadow_memory_dynamic_address + kAliasRegionOffset;
+
+  CHECK_EQ(AliasRegionStart >> kTaggableRegionCheckShift,
+           __hwasan_shadow_memory_dynamic_address >> kTaggableRegionCheckShift);
+  CHECK_EQ(
+      (AliasRegionStart + kAliasRegionOffset - 1) >> kTaggableRegionCheckShift,
+      __hwasan_shadow_memory_dynamic_address >> kTaggableRegionCheckShift);
+  return AliasRegionStart;
+#else
+  return 0;
+#endif
+}
+
 void HwasanAllocatorInit() {
   atomic_store_relaxed(&hwasan_allocator_tagging_enabled,
                        !flags()->disable_allocator_tagging);
   SetAllocatorMayReturnNull(common_flags()->allocator_may_return_null);
   allocator.Init(common_flags()->allocator_release_to_os_interval_ms,
-                 kAliasRegionStart);
+                 GetAliasRegionStart());
   for (uptr i = 0; i < sizeof(tail_magic); i++)
     tail_magic[i] = GetCurrentThread()->GenerateRandomTag();
 }
diff --git a/compiler-rt/lib/hwasan/hwasan_linux.cpp b/compiler-rt/lib/hwasan/hwasan_linux.cpp
index c1569b9..e227235 100644
--- a/compiler-rt/lib/hwasan/hwasan_linux.cpp
+++ b/compiler-rt/lib/hwasan/hwasan_linux.cpp
@@ -72,8 +72,6 @@ uptr kLowMemEnd;
 uptr kHighMemStart;
 uptr kHighMemEnd;
 
-uptr kAliasRegionStart;  // Always 0 when aliases aren't used.
-
 static void PrintRange(uptr start, uptr end, const char *name) {
   Printf("|| [%p, %p] || %.*s ||\n", (void *)start, (void *)end, 10, name);
 }
@@ -194,18 +192,6 @@ bool InitShadow() {
   // High memory starts where allocated shadow allows.
   kHighMemStart = ShadowToMem(kHighShadowStart);
 
-#  if defined(HWASAN_ALIASING_MODE)
-  constexpr uptr kAliasRegionOffset = 1ULL << (kTaggableRegionCheckShift - 1);
-  kAliasRegionStart =
-      __hwasan_shadow_memory_dynamic_address + kAliasRegionOffset;
-
-  CHECK_EQ(kAliasRegionStart >> kTaggableRegionCheckShift,
-           __hwasan_shadow_memory_dynamic_address >> kTaggableRegionCheckShift);
-  CHECK_EQ(
-      (kAliasRegionStart + kAliasRegionOffset - 1) >> kTaggableRegionCheckShift,
-      __hwasan_shadow_memory_dynamic_address >> kTaggableRegionCheckShift);
-#  endif
-
   // Check the sanity of the defined memory ranges (there might be gaps).
   CHECK_EQ(kHighMemStart % GetMmapGranularity(), 0);
   CHECK_GT(kHighMemStart, kHighShadowEnd);
diff --git a/compiler-rt/lib/hwasan/hwasan_mapping.h b/compiler-rt/lib/hwasan/hwasan_mapping.h
index fae66d5..79a1436 100644
--- a/compiler-rt/lib/hwasan/hwasan_mapping.h
+++ b/compiler-rt/lib/hwasan/hwasan_mapping.h
@@ -48,8 +48,6 @@ extern uptr kHighShadowEnd;
 extern uptr kHighMemStart;
 extern uptr kHighMemEnd;
 
-extern uptr kAliasRegionStart;
-
 inline uptr GetShadowOffset() {
   return SANITIZER_FUCHSIA ? 0 : __hwasan_shadow_memory_dynamic_address;
 }
@@ -70,6 +68,8 @@ inline bool MemIsShadow(uptr p) {
          (kHighShadowStart <= p && p <= kHighShadowEnd);
 }
 
+uptr GetAliasRegionStart();
+
 }  // namespace __hwasan
 
 #endif  // HWASAN_MAPPING_H
-- 
2.7.4