[llvm-objcopy] Allow strip symtab in executables and DSOs

Re-commit of the patch after addressing -Wl,--emit-relocs case.
Differential revision: https://reviews.llvm.org/D61672

llvm-svn: 366787

1 files changed, 21 insertions, 0 deletions

diff --git a/llvm/tools/llvm-objcopy/ELF/Object.cpp b/llvm/tools/llvm-objcopy/ELF/Object.cpp
index fa69638..2d85b3a 100644
--- a/llvm/tools/llvm-objcopy/ELF/Object.cpp
+++ b/llvm/tools/llvm-objcopy/ELF/Object.cpp
@@ -1995,6 +1995,25 @@ template <class ELFT> Error ELFWriter<ELFT>::write() {
   return Buf.commit();
 }
 
+static Error removeUnneededSections(Object &Obj) {
+  // We can remove an empty symbol table from non-relocatable objects.
+  // Relocatable objects typically have relocation sections whose
+  // sh_link field points to .symtab, so we can't remove .symtab
+  // even if it is empty.
+  if (Obj.isRelocatable() || Obj.SymbolTable == nullptr ||
+      !Obj.SymbolTable->empty())
+    return Error::success();
+
+  // .strtab can be used for section names. In such a case we shouldn't
+  // remove it.
+  auto *StrTab = Obj.SymbolTable->getStrTab() == Obj.SectionNames
+                     ? nullptr
+                     : Obj.SymbolTable->getStrTab();
+  return Obj.removeSections(false, [&](const SectionBase &Sec) {
+    return &Sec == Obj.SymbolTable || &Sec == StrTab;
+  });
+}
+
 template <class ELFT> Error ELFWriter<ELFT>::finalize() {
   // It could happen that SectionNames has been removed and yet the user wants
   // a section header table output. We need to throw an error if a user tries
@@ -2004,6 +2023,8 @@ template <class ELFT> Error ELFWriter<ELFT>::finalize() {
                              "cannot write section header table because "
                              "section header string table was removed");
 
+  if (Error E = removeUnneededSections(Obj))
+    return E;
   Obj.sortSections();
 
   // We need to assign indexes before we perform layout because we need to know