[PATCH] D106782: [llvm-objcopy] Drop GRP_COMDAT if the group signature is localized

[Fangrui Song via Phabricator via llvm-commits]

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See GRP_COMDAT group with STB_LOCAL signature <https://groups.google.com/g/generic-abi/c/2X6mR-s2zoc>

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.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D106782

Files:
  llvm/test/tools/llvm-objcopy/ELF/group-reorder.test
  llvm/test/tools/llvm-objcopy/ELF/group.test
  llvm/test/tools/llvm-objcopy/ELF/remove-section-in-group.test
  llvm/test/tools/llvm-objcopy/ELF/strip-dwo-groups.test
  llvm/tools/llvm-objcopy/ELF/Object.cpp


Index: llvm/tools/llvm-objcopy/ELF/Object.cpp
===================================================================
--- llvm/tools/llvm-objcopy/ELF/Object.cpp
+++ llvm/tools/llvm-objcopy/ELF/Object.cpp
@@ -1069,6 +1069,12 @@
 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.
+  if ((FlagWord & GRP_COMDAT) && Sym && Sym->Binding == STB_LOCAL)
+    this->FlagWord &= ~GRP_COMDAT;
 }
 
 Error GroupSection::removeSectionReferences(
Index: llvm/test/tools/llvm-objcopy/ELF/strip-dwo-groups.test
===================================================================
--- llvm/test/tools/llvm-objcopy/ELF/strip-dwo-groups.test
+++ llvm/test/tools/llvm-objcopy/ELF/strip-dwo-groups.test
@@ -75,9 +75,11 @@
 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
Index: llvm/test/tools/llvm-objcopy/ELF/remove-section-in-group.test
===================================================================
--- llvm/test/tools/llvm-objcopy/ELF/remove-section-in-group.test
+++ llvm/test/tools/llvm-objcopy/ELF/remove-section-in-group.test
@@ -34,3 +34,4 @@
 Symbols:
   - Name:     foo_bar_grp
     Section:  .group
+    Binding:  STB_GLOBAL
Index: llvm/test/tools/llvm-objcopy/ELF/group.test
===================================================================
--- llvm/test/tools/llvm-objcopy/ELF/group.test
+++ llvm/test/tools/llvm-objcopy/ELF/group.test
@@ -78,3 +78,23 @@
 ## sh_info fields.
 # RUN: llvm-objcopy --allow-broken-links -R .symtab %t3 %t4
 # RUN: cmp %t3 %t4
+
+## The signature symbol is 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 is non-local. Keep GRP_COMDAT.
+# RUN: llvm-readelf -s --section-groups %t | 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:
Index: llvm/test/tools/llvm-objcopy/ELF/group-reorder.test
===================================================================
--- llvm/test/tools/llvm-objcopy/ELF/group-reorder.test
+++ llvm/test/tools/llvm-objcopy/ELF/group-reorder.test
@@ -61,4 +61,5 @@
     Section:         .bar
   - Name:            bar
     Type:            STT_FUNC
+    Binding:         STB_GLOBAL
     Section:         .foo


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