[PATCH] D90108: [MC] Error for .weak/.globl/.local which change the symbol binding

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added reviewers: jhenderson, nickdesaulniers, psmith.
Herald added subscribers: llvm-commits, steven.zhang, hiraditya, emaste.
Herald added a reviewer: espindola.
Herald added a project: LLVM.
MaskRay requested review of this revision.

GNU as let .weak override .globl since binutils-gdb
5ca547dc2399a0a5d9f20626d4bf5547c3ccfddd (1996) while MC lets the last
directive win (PR38921).

This caused an issue to Linux's powerpc port which has been fixed by
http://git.kernel.org/linus/968339fad422a58312f67718691b717dac45c399

Binding overriding is error-prone. This patch disallows a changed binding.
(https://sourceware.org/pipermail/binutils/2020-March/000299.html )


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D90108

Files:
  llvm/lib/MC/MCELFStreamer.cpp
  llvm/test/MC/ELF/symbol-binding-changed.s


Index: llvm/test/MC/ELF/symbol-binding-changed.s
===================================================================
--- /dev/null
+++ llvm/test/MC/ELF/symbol-binding-changed.s
@@ -0,0 +1,27 @@
+# RUN: not llvm-mc -filetype=obj -triple=x86_64 %s -o /dev/null 2>&1 | FileCheck %s --implicit-check-not=error:
+
+# CHECK: error: local changed binding to STB_GLOBAL
+local:
+.local local
+.globl local
+
+# CHECK: error: global changed binding to STB_WEAK
+global:
+.global global
+.weak global
+
+# CHECK: error: weak changed binding to STB_LOCAL
+weak:
+.weak weak
+.local weak
+
+# CHECK-NOT: error:
+multi_local:
+.local multi_local
+.local multi_local
+multi_global:
+.global multi_global
+.global multi_global
+multi_weak:
+.weak multi_weak
+.weak multi_weak
Index: llvm/lib/MC/MCELFStreamer.cpp
===================================================================
--- llvm/lib/MC/MCELFStreamer.cpp
+++ llvm/lib/MC/MCELFStreamer.cpp
@@ -225,17 +225,26 @@
     break;
 
   case MCSA_Global:
+    if (Symbol->isBindingSet() && Symbol->getBinding() != ELF::STB_GLOBAL)
+      getContext().reportError(SMLoc(), Symbol->getName() +
+                                            " changed binding to STB_GLOBAL");
     Symbol->setBinding(ELF::STB_GLOBAL);
     Symbol->setExternal(true);
     break;
 
   case MCSA_WeakReference:
   case MCSA_Weak:
+    if (Symbol->isBindingSet() && Symbol->getBinding() != ELF::STB_WEAK)
+      getContext().reportError(SMLoc(), Symbol->getName() +
+                                            " changed binding to STB_WEAK");
     Symbol->setBinding(ELF::STB_WEAK);
     Symbol->setExternal(true);
     break;
 
   case MCSA_Local:
+    if (Symbol->isBindingSet() && Symbol->getBinding() != ELF::STB_LOCAL)
+      getContext().reportError(SMLoc(), Symbol->getName() +
+                                            " changed binding to STB_LOCAL");
     Symbol->setBinding(ELF::STB_LOCAL);
     Symbol->setExternal(false);
     break;


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