[Kaleidoscope] Fix race condition in order-of-destruction between Sec…

…tionMemoryManager and its MemoryMapper

SectionMemoryManager's default memory mapper used to be a global static
object. If the SectionMemoryManager itself is a global static
object, it might be destroyed after its memory mapper and thus couldn't
use it from the destructor.

The Kaleidoscope tutorial reproduced this situation with MSVC for a long time.
Since 47f5c54 it's triggered with GCC as well. The solution from
this patch was proposed in the existing review https://reviews.llvm.org/D107087
before, but it didn't move forward.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D154338

llvm/include/llvm/ExecutionEngine/SectionMemoryManager.h

@@ -185,7 +185,8 @@ class SectionMemoryManager : public RTDyldMemoryManager {
   MemoryGroup CodeMem;
   MemoryGroup RWDataMem;
   MemoryGroup RODataMem;
-  MemoryMapper &MMapper;
+  MemoryMapper *MMapper;
+  std::unique_ptr<MemoryMapper> OwnedMMapper;
 };
 
 } // end namespace llvm

llvm/lib/ExecutionEngine/SectionMemoryManager.cpp

@@ -101,7 +101,7 @@ uint8_t *SectionMemoryManager::allocateSection(
   // FIXME: Initialize the Near member for each memory group to avoid
   // interleaving.
   std::error_code ec;
-  sys::MemoryBlock MB = MMapper.allocateMappedMemory(
+  sys::MemoryBlock MB = MMapper->allocateMappedMemory(
       Purpose, RequiredSize, &MemGroup.Near,
       sys::Memory::MF_READ | sys::Memory::MF_WRITE, ec);
   if (ec) {
@@ -204,7 +204,7 @@ std::error_code
 SectionMemoryManager::applyMemoryGroupPermissions(MemoryGroup &MemGroup,
                                                   unsigned Permissions) {
   for (sys::MemoryBlock &MB : MemGroup.PendingMem)
-    if (std::error_code EC = MMapper.protectMappedMemory(MB, Permissions))
+    if (std::error_code EC = MMapper->protectMappedMemory(MB, Permissions))
       return EC;
 
   MemGroup.PendingMem.clear();
@@ -234,7 +234,7 @@ void SectionMemoryManager::invalidateInstructionCache() {
 SectionMemoryManager::~SectionMemoryManager() {
   for (MemoryGroup *Group : {&CodeMem, &RWDataMem, &RODataMem}) {
     for (sys::MemoryBlock &Block : Group->AllocatedMem)
-      MMapper.releaseMappedMemory(Block);
+      MMapper->releaseMappedMemory(Block);
   }
 }
 
@@ -263,11 +263,14 @@ class DefaultMMapper final : public SectionMemoryManager::MemoryMapper {
     return sys::Memory::releaseMappedMemory(M);
   }
 };
-
-DefaultMMapper DefaultMMapperInstance;
 } // namespace
 
-SectionMemoryManager::SectionMemoryManager(MemoryMapper *MM)
-    : MMapper(MM ? *MM : DefaultMMapperInstance) {}
+SectionMemoryManager::SectionMemoryManager(MemoryMapper *UnownedMM)
+    : MMapper(UnownedMM), OwnedMMapper(nullptr) {
+  if (!MMapper) {
+    OwnedMMapper = std::make_unique<DefaultMMapper>();
+    MMapper = OwnedMMapper.get();
+  }
+}
 
 } // namespace llvm