[compiler-rt][hwasan] Add GetShadowOffset function

[leonardchan]

Summary

Similar to SHADOW_OFFSET on asan, we can use this for hwasan so platforms that use a constant value for the start of shadow memory can just use the constant rather than access a global.

[vitalybuka]

compiler-rt/lib/hwasan/hwasan_mapping.h

51

Maybe the following to minimize code which compiles only on limited set of platforms?

inline uptr GetShadowOffset() {
  return SANITIZER_FUCHSIA ? 0 : __hwasan_shadow_memory_dynamic_address;
}

56–57

clang-tidy: error: expected ';' after return statement [clang-diagnostic-error]

please fix

[mcgrathr]

compiler-rt/lib/hwasan/hwasan_mapping.h

54

I think you'll eventually need to make this an #if or if constexpr for it to be kosher that the symbol isn't defined at all, which is what we'd ideally like to have on Fuchsia.

[vitalybuka]

compiler-rt/lib/hwasan/hwasan_mapping.h

54

static inline?

[mcgrathr]

compiler-rt/lib/hwasan/hwasan_mapping.h

54

Plain inline has correct semantics here, and is consistent with the existing functions below.
static inside namespace scope in a header is a strange thing to do.

[vitalybuka]

compiler-rt/lib/hwasan/hwasan_mapping.h

54

that's exactly the point: inline and no exported symbol
you can find many of then in llvm headers.

compiler-rt/lib/hwasan/hwasan_allocator.h

 //
 //===----------------------------------------------------------------------===//
 
 #ifndef HWASAN_ALLOCATOR_H
 #define HWASAN_ALLOCATOR_H
 
 #include "hwasan.h"
 #include "hwasan_interface_internal.h"
+#include "hwasan_mapping.h"
 #include "hwasan_poisoning.h"
 #include "sanitizer_common/sanitizer_allocator.h"
 #include "sanitizer_common/sanitizer_allocator_checks.h"
 #include "sanitizer_common/sanitizer_allocator_interface.h"
 #include "sanitizer_common/sanitizer_allocator_report.h"
 #include "sanitizer_common/sanitizer_common.h"
 #include "sanitizer_common/sanitizer_ring_buffer.h"
 

 
 void GetAllocatorStats(AllocatorStatCounters s);
 
 inline bool InTaggableRegion(uptr addr) {
 #if defined(HWASAN_ALIASING_MODE)
   // Aliases are mapped next to shadow so that the upper bits match the shadow
   // base.
   return (addr >> kTaggableRegionCheckShift) ==
-         (__hwasan_shadow_memory_dynamic_address >> kTaggableRegionCheckShift);
+         (GetShadowOffset() >> kTaggableRegionCheckShift);
 #endif
   return true;
 }
 
 } // namespace __hwasan
 
 #endif // HWASAN_ALLOCATOR_H

compiler-rt/lib/hwasan/hwasan_mapping.h

 extern uptr kLowMemEnd;
 extern uptr kLowShadowEnd;
 extern uptr kLowShadowStart;
 extern uptr kHighShadowStart;
 extern uptr kHighShadowEnd;
 extern uptr kHighMemStart;
 extern uptr kHighMemEnd;
 
 extern uptr kAliasRegionStart;
 
+inline uptr GetShadowOffset() {
+  return SANITIZER_FUCHSIA ? 0 : __hwasan_shadow_memory_dynamic_address;
+}
 inline uptr MemToShadow(uptr untagged_addr) {
-  return (untagged_addr >> kShadowScale) +
-         __hwasan_shadow_memory_dynamic_address;
+  return (untagged_addr >> kShadowScale) + GetShadowOffset();
 }
 inline uptr ShadowToMem(uptr shadow_addr) {
-  return (shadow_addr - __hwasan_shadow_memory_dynamic_address) << kShadowScale;
+  return (shadow_addr - GetShadowOffset()) << kShadowScale;
 }
 inline uptr MemToShadowSize(uptr size) {
   return size >> kShadowScale;
 }
 
 bool MemIsApp(uptr p);
 
 }  // namespace __hwasan
 
 #endif  // HWASAN_MAPPING_H