[PATCH] D110609: [CodeGen] Fix wrapping personality symbol on ARM

[Shoaib Meenai via Phabricator via llvm-commits]

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The ARM backend was explicitly setting global binding on the personality
symbol. This was added without any comment in a7ec2dcefd954, which
introduced EHABI support (back in 2011). None of the other backends do
anything equivalent, as far as I can tell.

This causes problems when attempting to wrap the personality symbol.
Wrapped symbols are marked as weak inside LTO to inhibit IPO (see
https://reviews.llvm.org/D33621). When we wrap the personality symbol,
it initially gets weak binding, and then the ARM backend attempts to
change the binding to global, which causes an error.

Simply drop the ARM backend's explicit global binding setting to fix
this. This matches all the other backends, and a large internal
application successfully linked and ran with this change, so it
shouldn't cause any problems. Test via LLD, since wrapping is required
to exhibit the issue.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D110609

Files:
  lld/test/ELF/arm-lto-wrap-personality.ll
  llvm/lib/CodeGen/AsmPrinter/ARMException.cpp


Index: llvm/lib/CodeGen/AsmPrinter/ARMException.cpp
===================================================================
--- llvm/lib/CodeGen/AsmPrinter/ARMException.cpp
+++ llvm/lib/CodeGen/AsmPrinter/ARMException.cpp
@@ -75,7 +75,6 @@
     // Emit references to personality.
     if (Per) {
       MCSymbol *PerSym = Asm->getSymbol(Per);
-      Asm->OutStreamer->emitSymbolAttribute(PerSym, MCSA_Global);
       ATS.emitPersonality(PerSym);
     }
 
Index: lld/test/ELF/arm-lto-wrap-personality.ll
===================================================================
--- /dev/null
+++ lld/test/ELF/arm-lto-wrap-personality.ll
@@ -0,0 +1,29 @@
+; Wrapped symbols are marked as weak for LTO to inhibit IPO. The ARM backend was
+; previously explicitly marking the personality function as global, so if we
+; attempted to wrap the personality function, its initial binding would be weak
+; and then the ARM backend would attempt to change it to global, causing an
+; error. Verify that the ARM backend no longer does this and we can successfully
+; wrap the personality symbol.
+
+; REQUIRES: arm
+
+; RUN: llvm-as -o %t %s
+; RUN: ld.lld -shared --wrap __gxx_personality_v0 %t
+
+target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "armv7-none-linux-android"
+
+define i32 @__gxx_personality_v0(...) {
+  ret i32 0
+}
+
+define void @dummy() optnone noinline personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
+  invoke void @dummy() to label %cont unwind label %lpad
+
+cont:
+  ret void
+
+lpad:
+  %lp = landingpad { i8*, i32 } cleanup
+  resume { i8*, i32 } %lp
+}


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