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[GlobalValue] Make dso_local function work with comdat nodeduplicate 

This fixes -fno-semantic-interposition -fsanitize-coverage incompatibility.

-fPIC -fno-semantic-interposition may add dso_local to an external linkage
function. -fsanitize-coverage instrumentation does not clear dso_local when
adding comdat nodeduplicate. This causes a compatibility issue: the function
symbol may be referenced by a PC-relative relocation without using the local
alias. In -shared mode, ld will report a relocation error.

The fix is to either clear dso_local when adding comdat nodeduplicate, or
supporting comdat nodeduplicate. The latter is more appropriate, because a
comdat nodeduplicate is like not using comdat.

Note: The comdat condition was originally added by D77429 to not use local alias
for a hidden external linkage function in a deduplicate comdat. The condition
has been unused since the code was refactored to only use local alias for
default visibility symbols.
Note: `canBenefitFromLocalAlias` is used by clang/lib/CodeGen/CodeGenModule.cpp
and we don't want to add dso_local to default visibility external linkage comdat any
(clang/test/CodeGenCUDA/usual-deallocators.cu).

Differential Revision: https://reviews.llvm.org/D117190
This commit is contained in:
Fangrui Song 2022-01-13 16:37:14 -08:00
parent 0f500d3dae
commit bc56097817
2 changed files with 33 additions and 2 deletions
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9
llvm/lib/IR/Globals.cpp
View File

@ -105,10 +105,15 @@ bool GlobalValue::isInterposable() const {
}
bool GlobalValue::canBenefitFromLocalAlias() const {
// See AsmPrinter::getSymbolPreferLocal().
// See AsmPrinter::getSymbolPreferLocal(). For a deduplicate comdat kind,
// references to a discarded local symbol from outside the group are not
// allowed, so avoid the local alias.
auto isDeduplicateComdat = [](const Comdat *C) {
return C && C->getSelectionKind() != Comdat::NoDeduplicate;
};
return hasDefaultVisibility() &&
GlobalObject::isExternalLinkage(getLinkage()) && !isDeclaration() &&
!isa<GlobalIFunc>(this) && !hasComdat();
!isa<GlobalIFunc>(this) && !isDeduplicateComdat(getComdat());
}
unsigned GlobalValue::getAddressSpace() const {

26
llvm/test/CodeGen/X86/linux-preemption.ll
View File

@ -252,6 +252,32 @@ define void()* @get_external_preemptable_function() {
; STATIC: movq external_preemptable_function@GOTPCREL(%rip), %rax
; CHECK32: movl external_preemptable_function@GOT(%eax), %eax
$comdat_nodeduplicate_local = comdat nodeduplicate
$comdat_nodeduplicate_preemptable = comdat nodeduplicate
$comdat_any_local = comdat any
;; -fpic -fno-semantic-interposition may add dso_local. Some instrumentation
;; may add comdat nodeduplicate. We should use local aliases to make the symbol
;; non-preemptible in the linker.
define dso_local i8* @comdat_nodeduplicate_local() comdat {
ret i8* bitcast (i8* ()* @comdat_nodeduplicate_local to i8*)
}
; CHECK: leaq .Lcomdat_nodeduplicate_local$local(%rip), %rax
; STATIC: movl $comdat_nodeduplicate_local, %eax
define dso_preemptable i8* @comdat_nodeduplicate_preemptable() comdat {
ret i8* bitcast (i8* ()* @comdat_nodeduplicate_preemptable to i8*)
}
; CHECK: movq comdat_nodeduplicate_preemptable@GOTPCREL(%rip), %rax
; STATIC: movq comdat_nodeduplicate_preemptable@GOTPCREL(%rip), %rax
;; Check the behavior for the invalid construct.
define dso_local i8* @comdat_any_local() comdat {
ret i8* bitcast (i8* ()* @comdat_any_local to i8*)
}
; CHECK: leaq comdat_any_local(%rip), %rax
; STATIC: movl $comdat_any_local, %eax
!llvm.module.flags = !{!0}
!0 = !{i32 7, !"PIC Level", i32 2}