[PATCH] D149243: [BOLT] Make sure all section allocations have deterministic contents

[Job Noorman via Phabricator via llvm-commits]

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For empty sections, RuntimeDyld always allocates 1 byte but leaves it
uninitialized. This causes the contents of some output sections to be
non-deterministic.

Note that this issue is also solved by D147544 <https://reviews.llvm.org/D147544>.

Fixes 59008


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D149243

Files:
  bolt/lib/Rewrite/ExecutableFileMemoryManager.cpp


Index: bolt/lib/Rewrite/ExecutableFileMemoryManager.cpp
===================================================================
--- bolt/lib/Rewrite/ExecutableFileMemoryManager.cpp
+++ bolt/lib/Rewrite/ExecutableFileMemoryManager.cpp
@@ -27,6 +27,12 @@
   uint8_t *Ret = static_cast<uint8_t *>(llvm::allocate_buffer(Size, Alignment));
   AllocatedSections.push_back(AllocInfo{Ret, Size, Alignment});
 
+  // A Size of 1 might mean an empty section for which RuntimeDyld decided to
+  // allocate 1 byte. In this case, the allocation will never be initialized
+  // causing non-deterministic output section contents.
+  if (Size == 1)
+    *Ret = 0;
+
   // Register a debug section as a note section.
   if (!ObjectsLoaded && RewriteInstance::isDebugSection(SectionName)) {
     BinarySection &Section =


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