[llvm-objcopy] Drop GRP_COMDAT if the group signature is localized

See [GRP_COMDAT group with STB_LOCAL signature](https://groups.google.com/g/generic-abi/c/2X6mR-s2zoc) objcopy PR: https://sourceware.org/bugzilla/show_bug.cgi?id=27931 GRP_COMDAT deduplication is purely based on the signature symbol name in ld.lld/GNU ld/gold. The local/global status is not part of the equation. If the signature symbol is localized by --localize-hidden or --keep-global-symbol, the intention is likely to make the group fully localized. Drop GRP_COMDAT to suppress deduplication. Reviewed By: jhenderson Differential Revision: https://reviews.llvm.org/D106782

Author: MaskRay

llvm/test/tools/llvm-objcopy/ELF/group-reorder.test

@@ -61,4 +61,5 @@ Symbols:
  Section: .bar
  - Name: bar
  Type: STT_FUNC
+ Binding: STB_GLOBAL
  Section: .foo

llvm/test/tools/llvm-objcopy/ELF/group.test

@@ -78,3 +78,52 @@ Symbols:
 ## sh_info fields.
 # RUN: llvm-objcopy --allow-broken-links -R .symtab %t3 %t4
 # RUN: cmp %t3 %t4
+
+## The signature symbol becomes local. Assume the intention is to localize the group.
+## Drop GRP_COMDAT so that the linker will suppress deduplication.
+# RUN: llvm-objcopy --keep-global-symbol=bar %t %t5
+# RUN: llvm-readelf -s --section-groups %t5 | FileCheck %s --check-prefix=LOCAL-SIG
+
+# LOCAL-SIG: LOCAL DEFAULT [[#]] foo
+# LOCAL-SIG: (unknown) group section [ 1] `.group' [foo] contains 1 sections:
+
+## The signature symbol remains non-local. Keep GRP_COMDAT.
+# RUN: llvm-readelf -s --section-groups %t1 | FileCheck %s --check-prefix=WEAK-SIG
+
+# WEAK-SIG: WEAK DEFAULT [[#]] foo
+# WEAK-SIG: COMDAT group section [ 1] `.group' [foo] contains 1 sections:
+
+# RUN: llvm-objcopy --globalize-symbol=foo %t %t6
+# RUN: llvm-readelf -s --section-groups %t6 | FileCheck %s --check-prefix=GLOBAL-SIG
+
+# GLOBAL-SIG: GLOBAL DEFAULT [[#]] foo
+# GLOBAL-SIG: COMDAT group section [ 1] `.group' [foo] contains 1 sections:
+
+## If the signature is initially local and no operation has been performed to
+## specifically localize it, it isn't clear whether we should drop GRP_COMDAT.
+## The current convention is that compilers should not produce such input, so
+## our choice does not matter.
+# RUN: yaml2obj --docnum=2 %s -o %t.localsig
+# RUN: llvm-objcopy %t.localsig %t.localsig.out
+# RUN: llvm-readelf -s --section-groups %t.localsig.out | FileCheck %s --check-prefix=LOCAL-SIG
+
+--- !ELF
+FileHeader:
+ Class: ELFCLASS64
+ Data: ELFDATA2LSB
+ Type: ET_REL
+ Machine: EM_X86_64
+Sections:
+ - Name: .group
+ Type: SHT_GROUP
+ Info: foo
+ Members:
+ - SectionOrType: GRP_COMDAT
+ - SectionOrType: .text.foo
+ - Name: .text.foo
+ Type: SHT_PROGBITS
+ Flags: [ SHF_GROUP ]
+Symbols:
+ - Name: foo
+ Type: STT_FUNC
+ Section: .text.foo

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

@@ -34,3 +34,4 @@ Sections:
 Symbols:
  - Name: foo_bar_grp
  Section: .group
+ Binding: STB_GLOBAL

llvm/test/tools/llvm-objcopy/ELF/strip-dwo-groups.test

@@ -75,9 +75,11 @@ Sections:
 Symbols:
  - Name: debug_before
  Section: .debug_before.dwo
+ - Name: debug_after
+ Section: .debug_after.dwo
  - Name: group2
  Section: .text.group2
+ Binding: STB_WEAK
  - Name: group1
  Section: .text.group1
- - Name: debug_after
- Section: .debug_after.dwo
+ Binding: STB_WEAK

llvm/tools/llvm-objcopy/ELF/Object.cpp

@@ -1069,6 +1069,12 @@ Error Section::removeSectionReferences(
 void GroupSection::finalize() {
  this->Info = Sym ? Sym->Index : 0;
  this->Link = SymTab ? SymTab->Index : 0;
+ // Linker deduplication for GRP_COMDAT is based on Sym->Name. The local/global
+ // status is not part of the equation. If Sym is localized, the intention is
+ // likely to make the group fully localized. Drop GRP_COMDAT to suppress
+ // deduplication. See https://groups.google.com/g/generic-abi/c/2X6mR-s2zoc
+ if ((FlagWord & GRP_COMDAT) && Sym && Sym->Binding == STB_LOCAL)
+ this->FlagWord &= ~GRP_COMDAT;
 }
 
 Error GroupSection::removeSectionReferences(