Revert "[llvm-objcopy] Remove empty SHT_GROUP sections (llvm#97141)"

This reverts commit 359c64f.

This caused heap-use-after-free. See llvm#98106.

llvm/lib/ObjCopy/ELF/ELFObject.cpp

@@ -2239,17 +2239,8 @@ Error Object::removeSections(
   // Transfer removed sections into the Object RemovedSections container for use
   // later.
   std::move(Iter, Sections.end(), std::back_inserter(RemovedSections));
-  // Now get rid of them altogether.
+  // Now finally get rid of them all together.
   Sections.erase(Iter, std::end(Sections));
-
-  // Finally erase empty SHT_GROUP sections.
-  llvm::erase_if(Sections, [](const SecPtr &Sec) {
-    if (auto GroupSec = dyn_cast<GroupSection>(Sec.get()))
-      return GroupSec->getMembersCount() == 0;
-
-    return false;
-  });
-
   return Error::success();
 }
 

llvm/lib/ObjCopy/ELF/ELFObject.h

@@ -964,8 +964,6 @@ class GroupSection : public SectionBase {
       const DenseMap<SectionBase *, SectionBase *> &FromTo) override;
   void onRemove() override;
 
-  size_t getMembersCount() const { return GroupMembers.size(); }
-
   static bool classof(const SectionBase *S) {
     return S->OriginalType == ELF::SHT_GROUP;
   }

llvm/test/tools/llvm-objcopy/ELF/remove-section-in-group.test

@@ -1,6 +1,6 @@
 ## This checks that the group section is shrunk when its member is removed.
 
-# RUN: yaml2obj --docnum=1 %s -o - \
+# RUN: yaml2obj %s -o - \
 # RUN:   | llvm-objcopy -R .foo - - \
 # RUN:   | obj2yaml - \
 # RUN:   | FileCheck %s
@@ -35,51 +35,3 @@ Symbols:
   - Name:     foo_bar_grp
     Section:  .group
     Binding:  STB_GLOBAL
-
-# RUN: yaml2obj --docnum=2 %s -o %t
-# RUN: llvm-objcopy --remove-section=.debug_macro %t
-# RUN: llvm-readelf --section-groups %t | FileCheck %s --check-prefix=GROUP-REMOVED
-
---- !ELF
-FileHeader:
-  Class:      ELFCLASS64
-  Data:       ELFDATA2LSB
-  Type:       ET_REL
-  Machine:    EM_X86_64
-Sections:
-  - Name:     .group
-    Type:     SHT_GROUP
-    Info:     foo_grp
-    Members:
-      - SectionOrType:  GRP_COMDAT
-      - SectionOrType:  .debug_macro
-  - Name:     .debug_macro
-    Type:     SHT_PROGBITS
-    Flags:    [ SHF_GROUP ]
-Symbols:
-  - Name:     foo_grp
-    Section:  .group
-
-# GROUP-REMOVED: There are no section groups in this file.
-
-# RUN: yaml2obj --docnum=3 %s -o %t
-# RUN: llvm-objcopy --remove-section=.group %t
-# RUN: llvm-readelf --section-groups %t | FileCheck %s --check-prefix=EMPTY-GROUP-REMOVED
-
---- !ELF
-FileHeader:
-  Class:      ELFCLASS64
-  Data:       ELFDATA2LSB
-  Type:       ET_REL
-  Machine:    EM_X86_64
-Sections:
-  - Name:     .group
-    Type:     SHT_GROUP
-    Info:     foo_grp
-    Members:
-      - SectionOrType:  GRP_COMDAT
-Symbols:
-  - Name:     foo_grp
-    Section:  .group
-
-# EMPTY-GROUP-REMOVED: There are no section groups in this file.