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[CodeGen] Fix wrapping personality symbol on ARM 

The ARM backend was explicitly setting global binding on the personality
symbol. This was added without any comment in a7ec2dcefd, 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 in MC because of
attempting to change the binding of a symbol from non-global to global
(the error was added in https://reviews.llvm.org/D90108).

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.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D110609
This commit is contained in:
Shoaib Meenai 2021-09-27 20:10:23 -07:00
parent 38c42d42eb
commit f9b3c18e74
2 changed files with 34 additions and 1 deletions
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34
lld/test/ELF/lto/arm-wrap-personality.ll Normal file
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@ -0,0 +1,34 @@
;; 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.bc %s
; RUN: ld.lld -shared --wrap __gxx_personality_v0 %t.bc -o %t.so
; RUN: llvm-readelf --dyn-syms %t.so | FileCheck %s
; CHECK: GLOBAL {{.*}} __wrap___gxx_personality_v0
;; This should be GLOBAL when PR52004 is fixed.
; CHECK: WEAK {{.*}} __gxx_personality_v0
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
}

1
llvm/lib/CodeGen/AsmPrinter/ARMException.cpp
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@ -75,7 +75,6 @@ void ARMException::endFunction(const MachineFunction *MF) {
// Emit references to personality.
if (Per) {
MCSymbol *PerSym = Asm->getSymbol(Per);
Asm->OutStreamer->emitSymbolAttribute(PerSym, MCSA_Global);
ATS.emitPersonality(PerSym);
}