[scudo] The BaseAddr should be MappedBase in releasePagesToOS()

[Chia-hungDuan]

Summary

This is used to make MemMapDefault be compliant with legacy APIs.

[Chia-hungDuan]

@fabio-d , Could you please help with verifying this on Fuchsia if you would like to take this solution, thanks

compiler-rt/lib/scudo/standalone/mem_map.h

public:
   uptr getBaseImpl() { return Base; }
   uptr getCapacityImpl() { return Capacity; }
 
   void setMapPlatformData(MapPlatformData &NewData) { Data = NewData; }
 
 private:
   uptr Base = 0;
   uptr Capacity = 0;
+  uptr MappedBase = 0;
   MapPlatformData Data = {};
 };
 
 // This will be deprecated when every allocator has been supported by each
 // platform's `MemMap` implementation.
 class ReservedMemoryDefault final
     : public ReservedMemory<ReservedMemoryDefault, MemMapDefault> {
 public:

compiler-rt/lib/scudo/standalone/mem_map.cpp

 
 bool MemMapDefault::mapImpl(uptr Addr, uptr Size, const char *Name,
                             uptr Flags) {
   void *MappedAddr =
       ::scudo::map(reinterpret_cast<void *>(Addr), Size, Name, Flags, &Data);
   if (MappedAddr == nullptr)
     return false;
   Base = reinterpret_cast<uptr>(MappedAddr);
+  MappedBase = Base;
   Capacity = Size;
   return true;
 }
 
 void MemMapDefault::unmapImpl(uptr Addr, uptr Size) {
   if (Size == Capacity) {
-    Base = Capacity = 0;
+    Base = MappedBase = Capacity = 0;
   } else {
-    if (Base == Addr)
+    if (Base == Addr) {
       Base = Addr + Size;
+      MappedBase = MappedBase == 0 ? Base : Max(MappedBase, Base);
+    }
     Capacity -= Size;
   }
 
   ::scudo::unmap(reinterpret_cast<void *>(Addr), Size, UNMAP_ALL, &Data);
 }
 
 bool MemMapDefault::remapImpl(uptr Addr, uptr Size, const char *Name,
                               uptr Flags) {
-  void *RemappedAddr =
+  void *RemappedPtr =
       ::scudo::map(reinterpret_cast<void *>(Addr), Size, Name, Flags, &Data);
-  return reinterpret_cast<uptr>(RemappedAddr) == Addr;
+  const uptr RemappedAddr = reinterpret_cast<uptr>(RemappedPtr);
+  MappedBase = MappedBase == 0 ? RemappedAddr : Min(MappedBase, RemappedAddr);
+  return RemappedAddr == Addr;
 }
 
 void MemMapDefault::releaseAndZeroPagesToOSImpl(uptr From, uptr Size) {
-  return ::scudo::releasePagesToOS(Base, From - Base, Size, &Data);
+  DCHECK_NE(MappedBase, 0U);
+  DCHECK_GE(From, MappedBase);
+  return ::scudo::releasePagesToOS(MappedBase, From - MappedBase, Size, &Data);
 }
 
 void MemMapDefault::setMemoryPermissionImpl(uptr Addr, uptr Size, uptr Flags) {
   return ::scudo::setMemoryPermission(Addr, Size, Flags);
 }
 
 void ReservedMemoryDefault::releaseImpl() {
   ::scudo::unmap(reinterpret_cast<void *>(Base), Capacity, UNMAP_ALL, &Data);