[llvm-objcopy] - Strip undefined symbols if they are no longer referenced following --only-section

This is https://bugs.llvm.org/show_bug.cgi?id=40004.

In this patch I teach llvm-objcopy to remove undefined symbols if
them are not used anymore after applying -j/--only-section option.

Differential revision: https://reviews.llvm.org/D62317

llvm-svn: 361642

1 files changed, 7 insertions, 1 deletions

diff --git a/llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp b/llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
index b2e750d15f0..be25bd5ee43 100644
--- a/llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
+++ b/llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
@@ -387,7 +387,8 @@ static Error updateAndRemoveSymbols(const CopyConfig &Config, Object &Obj) {
   // The purpose of this loop is to mark symbols referenced by sections
   // (like GroupSection or RelocationSection). This way, we know which
   // symbols are still 'needed' and which are not.
-  if (Config.StripUnneeded || !Config.UnneededSymbolsToRemove.empty()) {
+  if (Config.StripUnneeded || !Config.UnneededSymbolsToRemove.empty() ||
+      !Config.OnlySection.empty()) {
     for (auto &Section : Obj.sections())
       Section.markSymbols();
   }
@@ -415,6 +416,11 @@ static Error updateAndRemoveSymbols(const CopyConfig &Config, Object &Obj) {
         isUnneededSymbol(Sym))
       return true;
 
+    // We want to remove undefined symbols if all references have been stripped.
+    if (!Config.OnlySection.empty() && !Sym.Referenced &&
+        Sym.getShndx() == SHN_UNDEF)
+      return true;
+
     return false;
   };