[llvm-objcopy][ELF] Fix removing a group member.

When a group member is removed, the corresponding record in the
SHT_GROUP section has to be deleted.

This fixes PR46064.

Differential Revision: https://reviews.llvm.org/D80568

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

@@ -0,0 +1,36 @@
+## This checks that the group section is shrunk when its member is removed.
+
+# RUN: yaml2obj %s -o - \
+# RUN:   | llvm-objcopy -R .foo - - \
+# RUN:   | obj2yaml - \
+# RUN:   | FileCheck %s
+
+# CHECK:      - Name: .group
+# CHECK:        Members:
+# CHECK-NEXT:     - SectionOrType:  GRP_COMDAT
+# CHECK-NEXT:     - SectionOrType:  .bar
+# CHECK-NOT:      - SectionOrType:
+
+--- !ELF
+FileHeader:
+  Class:      ELFCLASS64
+  Data:       ELFDATA2LSB
+  Type:       ET_REL
+  Machine:    EM_X86_64
+Sections:
+  - Name:     .group
+    Type:     SHT_GROUP
+    Info:     foo_bar_grp
+    Members:
+      - SectionOrType:  GRP_COMDAT
+      - SectionOrType:  .foo
+      - SectionOrType:  .bar
+  - Name:     .foo
+    Type:     SHT_PROGBITS
+    Flags:    [ SHF_ALLOC, SHF_GROUP ]
+  - Name:     .bar
+    Type:     SHT_PROGBITS
+    Flags:    [ SHF_ALLOC, SHF_GROUP ]
+Symbols:
+  - Name:     foo_bar_grp
+    Section:  .group

tools/llvm-objcopy/ELF/Object.cpp

@@ -112,7 +112,9 @@ void ELFSectionSizer<ELFT>::visit(RelocationSection &Sec) {
 template <class ELFT>
 void ELFSectionSizer<ELFT>::visit(GnuDebugLinkSection &Sec) {}
 
-template <class ELFT> void ELFSectionSizer<ELFT>::visit(GroupSection &Sec) {}
+template <class ELFT> void ELFSectionSizer<ELFT>::visit(GroupSection &Sec) {
+  Sec.Size = sizeof(Elf_Word) + Sec.GroupMembers.size() * sizeof(Elf_Word);
+}
 
 template <class ELFT>
 void ELFSectionSizer<ELFT>::visit(SectionIndexSection &Sec) {}
@@ -968,6 +970,12 @@ void GroupSection::finalize() {
   this->Link = SymTab->Index;
 }
 
+Error GroupSection::removeSectionReferences(
+    bool AllowBrokenLinks, function_ref<bool(const SectionBase *)> ToRemove) {
+  llvm::erase_if(GroupMembers, ToRemove);
+  return Error::success();
+}
+
 Error GroupSection::removeSymbols(function_ref<bool(const Symbol &)> ToRemove) {
   if (ToRemove(*Sym))
     return createStringError(llvm::errc::invalid_argument,

tools/llvm-objcopy/ELF/Object.h

@@ -801,6 +801,9 @@ public:
   void accept(SectionVisitor &) const override;
   void accept(MutableSectionVisitor &Visitor) override;
   void finalize() override;
+  Error removeSectionReferences(
+      bool AllowBrokenLinks,
+      function_ref<bool(const SectionBase *)> ToRemove) override;
   Error removeSymbols(function_ref<bool(const Symbol &)> ToRemove) override;
   void markSymbols() override;
   void replaceSectionReferences(