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GCC 11 will set SHF_GNU_RETAIN on the section of a `__attribute__((used))`
function/variable, if the configure-time GNU as supports SHF_GNU_RETAIN
(binutils 2.36 or above on Linux or FreeBSD).
This patch sets !retain metadata on UsedAttr definitions.
We let the backend to figure out whether the ELF section flag SHF_GNU_RETAIN
should be used (integrated assembler or `-fno-integrated-as
-fbinutils-version=2.36`).
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D96838
Files:
clang/lib/CodeGen/CGDecl.cpp
clang/lib/CodeGen/CodeGenModule.cpp
clang/lib/CodeGen/CodeGenModule.h
clang/test/CodeGen/attr-used.c
clang/test/CodeGenCXX/attr-used.cpp
Index: clang/test/CodeGenCXX/attr-used.cpp
===================================================================
--- clang/test/CodeGenCXX/attr-used.cpp
+++ clang/test/CodeGenCXX/attr-used.cpp
@@ -1,10 +1,13 @@
// RUN: %clang_cc1 -emit-llvm -triple %itanium_abi_triple -o - %s | FileCheck %s
+// RUN: %clang_cc1 -emit-llvm -triple x86_64-linux -o - %s | FileCheck %s --check-prefix=RETAIN
// <rdar://problem/8684363>: clang++ not respecting __attribute__((used)) on destructors
struct X0 {
// CHECK-DAG: define linkonce_odr {{.*}} @_ZN2X0C1Ev
+ // RETAIN-DAG: define linkonce_odr {{.*}} @_ZN2X0C1Ev({{.*}} !retain
__attribute__((used)) X0() {}
// CHECK-DAG: define linkonce_odr {{.*}} @_ZN2X0D1Ev
+ // RETAIN-DAG: define linkonce_odr {{.*}} @_ZN2X0D1Ev({{.*}} !retain
__attribute__((used)) ~X0() {}
};
@@ -12,6 +15,7 @@
struct X1 {
struct Nested {
// CHECK-DAG: define linkonce_odr {{.*}} @_ZN2X16Nested1fEv
+ // RETAIN-DAG: define linkonce_odr {{.*}} @_ZN2X16Nested1fEv({{.*}} !retain
void __attribute__((used)) f() {}
};
};
@@ -24,4 +28,5 @@
// CHECK-DAG: define linkonce_odr {{.*}} @_ZN2X23barEv
// CHECK-DAG: define linkonce_odr {{.*}} @_ZN2X23fooEv
+ // RETAIN-DAG: define linkonce_odr {{.*}} @_ZN2X23barEv({{.*}} !retain
};
Index: clang/test/CodeGen/attr-used.c
===================================================================
--- clang/test/CodeGen/attr-used.c
+++ clang/test/CodeGen/attr-used.c
@@ -1,10 +1,23 @@
-// RUN: %clang_cc1 -emit-llvm -o %t %s
-// RUN: grep '@llvm.used = .*@a0' %t
-// RUN: grep '@llvm.used = .*@g0' %t
-// RUN: grep '@llvm.used = .*@f0' %t
-// RUN: grep '@llvm.used = .*@f1.l0' %t
+// RUN: %clang_cc1 -emit-llvm -triple x86_64-linux %s -o - | FileCheck %s --check-prefixes=CHECK,RETAIN
+// RUN: %clang_cc1 -emit-llvm -triple x86_64-freebsd %s -o - | FileCheck %s --check-prefixes=CHECK,RETAIN
+// RUN: %clang_cc1 -emit-llvm -triple x86_64-apple-darwin %s -o - | FileCheck %s --check-prefixes=CHECK,NORETAIN
+// RETAIN: @r0 ={{.*}} constant i32 {{.*}} !retain ![[#EMPTY:]]
+// RETAIN: @f1.l0 = internal global i32 {{.*}} !retain ![[#EMPTY]]
+// RETAIN: @a0 ={{.*}} global i32 {{.*}} !retain ![[#EMPTY]]
+// RETAIN: @g0 ={{.*}} global i32 {{.*}} !retain ![[#EMPTY]]
+/// Set !retain only on Linux and FreeBSD.
+// NORETAIN-NOT: !retain
+
+// CHECK: @llvm.used ={{.*}} @f0
+// CHECK-SAME: @f1.l0
+// CHECK-SAME: @g0
+// CHECK-SAME: @a0
+
+// RETAIN: [[#EMPTY]] = !{}
+
+const int r0 __attribute__((used)) = 42;
int g0 __attribute__((used));
static void __attribute__((used)) f0(void) {
Index: clang/lib/CodeGen/CodeGenModule.h
===================================================================
--- clang/lib/CodeGen/CodeGenModule.h
+++ clang/lib/CodeGen/CodeGenModule.h
@@ -1048,6 +1048,9 @@
template<typename SomeDecl>
void MaybeHandleStaticInExternC(const SomeDecl *D, llvm::GlobalValue *GV);
+ /// Set !retain metadata if the target supports.
+ void maybeSetRetain(llvm::GlobalObject *GO);
+
/// Add a global to a list to be added to the llvm.used metadata.
void addUsedGlobal(llvm::GlobalValue *GV);
Index: clang/lib/CodeGen/CodeGenModule.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenModule.cpp
+++ clang/lib/CodeGen/CodeGenModule.cpp
@@ -1883,6 +1883,8 @@
if (D) {
if (auto *GV = dyn_cast<llvm::GlobalVariable>(GO)) {
+ if (D->hasAttr<UsedAttr>())
+ maybeSetRetain(GV);
if (auto *SA = D->getAttr<PragmaClangBSSSectionAttr>())
GV->addAttribute("bss-section", SA->getName());
if (auto *SA = D->getAttr<PragmaClangDataSectionAttr>())
@@ -1894,6 +1896,8 @@
}
if (auto *F = dyn_cast<llvm::Function>(GO)) {
+ if (D->hasAttr<UsedAttr>())
+ maybeSetRetain(F);
if (auto *SA = D->getAttr<PragmaClangTextSectionAttr>())
if (!D->getAttr<SectionAttr>())
F->addFnAttr("implicit-section-name", SA->getName());
@@ -2062,6 +2066,13 @@
}
}
+void CodeGenModule::maybeSetRetain(llvm::GlobalObject *GO) {
+ const llvm::Triple &T = getTarget().getTriple();
+ if (T.isOSFreeBSD() || T.isOSLinux())
+ GO->setMetadata(llvm::LLVMContext::MD_retain,
+ llvm::MDNode::get(getLLVMContext(), None));
+}
+
void CodeGenModule::addUsedGlobal(llvm::GlobalValue *GV) {
assert((isa<llvm::Function>(GV) || !GV->isDeclaration()) &&
"Only globals with definition can force usage.");
Index: clang/lib/CodeGen/CGDecl.cpp
===================================================================
--- clang/lib/CodeGen/CGDecl.cpp
+++ clang/lib/CodeGen/CGDecl.cpp
@@ -441,8 +441,10 @@
if (const SectionAttr *SA = D.getAttr<SectionAttr>())
var->setSection(SA->getName());
- if (D.hasAttr<UsedAttr>())
+ if (D.hasAttr<UsedAttr>()) {
CGM.addUsedGlobal(var);
+ CGM.maybeSetRetain(var);
+ }
// We may have to cast the constant because of the initializer
// mismatch above.
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