[llvm] [BOLT] Overwrite .eh_frame and .gcc_except_table (PR #116755)

[Maksim Panchenko via llvm-commits]

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@@ -3887,6 +3887,43 @@ void RewriteInstance::mapCodeSections(BOLTLinker::SectionMapper MapSection) {
 
 void RewriteInstance::mapAllocatableSections(
     BOLTLinker::SectionMapper MapSection) {
+
+  if (opts::UseOldText || opts::StrictMode) {
+    auto tryRewriteSection = [&](BinarySection &OldSection,
+                                 BinarySection &NewSection) {
+      if (OldSection.getSize() < NewSection.getOutputSize())
+        return;
+
+      BC->outs() << "BOLT-INFO: rewriting " << OldSection.getName()
+                 << " in-place\n";
+
+      NewSection.setOutputAddress(OldSection.getAddress());
+      NewSection.setOutputFileOffset(OldSection.getInputFileOffset());
+      MapSection(NewSection, OldSection.getAddress());
+
+      // Pad contents with zeros.
+      NewSection.addPadding(OldSection.getSize() - NewSection.getOutputSize());
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maksfb wrote:

Since we overwrite the original contents, if the new section is smaller, there will be leftovers from the original section left in the tail. Hence, we write zeros to remove "junk" bytes.

https://github.com/llvm/llvm-project/pull/116755