[llvm-objcopy][WebAssembly] Allow --strip-debug to operate on relocatable files. (#102978)upstream/main

This change is enough to allow `--strip-debug` to work on object files,
without breaking the relocation information or symbol table.

A more complete version of this change would instead reconstruct the
symbol table and relocation sections, but that is much larger change.

Bug: #102002

1 files changed, 16 insertions, 2 deletions

diff --git a/llvm/lib/ObjCopy/wasm/WasmObject.cpp b/llvm/lib/ObjCopy/wasm/WasmObject.cpp
index 28a2de6..0b543b7 100644
--- a/llvm/lib/ObjCopy/wasm/WasmObject.cpp
+++ b/llvm/lib/ObjCopy/wasm/WasmObject.cpp
@@ -25,8 +25,22 @@ void Object::addSectionWithOwnedContents(
 }
 
 void Object::removeSections(function_ref<bool(const Section &)> ToRemove) {
-  // TODO: remove reloc sections for the removed section, handle symbols, etc.
-  llvm::erase_if(Sections, ToRemove);
+  if (isRelocatableObject) {
+    // For relocatable objects, avoid actually removing any sections,
+    // since that can invalidate the symbol table and relocation sections.
+    // TODO: Allow removal of sections by re-generating symbol table and
+    // relocation sections here instead.
+    for (auto &Sec : Sections) {
+      if (ToRemove(Sec)) {
+        Sec.Name = ".objcopy.removed";
+        Sec.SectionType = wasm::WASM_SEC_CUSTOM;
+        Sec.Contents = {};
+        Sec.HeaderSecSizeEncodingLen = std::nullopt;
+      }
+    }
+  } else {
+    llvm::erase_if(Sections, ToRemove);
+  }
 }
 
 } // end namespace wasm