[llvm-branch-commits] [llvm] [clang] [clang] Support __attribute__((ifunc(...))) on Darwin platforms (PR #73687)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Jon Roelofs (jroelofs)

<details>
<summary>Changes</summary>

Unlike ELF targets, MachO does not support the same kind of dynamic symbol
resolution at load time.  Instead, the corresponding MachO feature resolves
symbols lazily on first call.


---
Full diff: https://github.com/llvm/llvm-project/pull/73687.diff


3 Files Affected:

- (modified) clang/include/clang/Basic/Attr.td (+4-1) 
- (modified) clang/include/clang/Basic/AttrDocs.td (+3-1) 
- (modified) clang/test/CodeGen/ifunc.c (+8) 


``````````diff
diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
index 03ed6accf700c4e..cef9f5578fa2baa 100644
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -455,6 +455,9 @@ def TargetMicrosoftCXXABI : TargetArch<["x86", "x86_64", "arm", "thumb", "aarch6
 def TargetELF : TargetSpec {
   let ObjectFormats = ["ELF"];
 }
+def TargetELFOrMachO : TargetSpec {
+  let ObjectFormats = ["ELF", "MachO"];
+}
 
 def TargetSupportsInitPriority : TargetSpec {
   let CustomCode = [{ !Target.getTriple().isOSzOS() }];
@@ -1665,7 +1668,7 @@ def IBOutletCollection : InheritableAttr {
   let Documentation = [Undocumented];
 }
 
-def IFunc : Attr, TargetSpecificAttr<TargetELF> {
+def IFunc : Attr, TargetSpecificAttr<TargetELFOrMachO> {
   let Spellings = [GCC<"ifunc">];
   let Args = [StringArgument<"Resolver">];
   let Subjects = SubjectList<[Function]>;
diff --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
index be74535e28d8a60..4c4c4eb606fb0dc 100644
--- a/clang/include/clang/Basic/AttrDocs.td
+++ b/clang/include/clang/Basic/AttrDocs.td
@@ -5408,7 +5408,9 @@ considered inline.
 Not all targets support this attribute. ELF target support depends on both the
 linker and runtime linker, and is available in at least lld 4.0 and later,
 binutils 2.20.1 and later, glibc v2.11.1 and later, and FreeBSD 9.1 and later.
-Non-ELF targets currently do not support this attribute.
+MachO targets support it, but with slightly different semantics: the resolver is
+run at first call, instead of at load time by the runtime linker. Targets other
+than ELF and MachO currently do not support this attribute.
   }];
 }
 
diff --git a/clang/test/CodeGen/ifunc.c b/clang/test/CodeGen/ifunc.c
index 0b0a0549620f8b8..99d60dc0ea85dbd 100644
--- a/clang/test/CodeGen/ifunc.c
+++ b/clang/test/CodeGen/ifunc.c
@@ -3,6 +3,10 @@
 // RUN: %clang_cc1 -triple i386-unknown-linux-gnu -fsanitize=thread -O2 -emit-llvm -o - %s | FileCheck %s --check-prefix=SAN
 // RUN: %clang_cc1 -triple i386-unknown-linux-gnu -fsanitize=address -O2 -emit-llvm -o - %s | FileCheck %s --check-prefix=SAN
 // RUN: %clang_cc1 -triple i386-unknown-linux-gnu -fsanitize=memory -O2 -emit-llvm -o - %s | FileCheck %s --check-prefix=SAN
+// RUN: %clang_cc1 -triple x86_64-apple-macosx -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx -O2 -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx -fsanitize=thread -O2 -emit-llvm -o - %s | FileCheck %s --check-prefix=MACSAN
+// RUN: %clang_cc1 -triple x86_64-apple-macosx -fsanitize=address -O2 -emit-llvm -o - %s | FileCheck %s --check-prefix=MACSAN
 
 int foo(int) __attribute__ ((ifunc("foo_ifunc")));
 
@@ -44,9 +48,13 @@ void* goo_ifunc(void) {
 // CHECK: call void @goo()
 
 // SAN: define internal nonnull ptr @foo_ifunc() #[[#FOO_IFUNC:]] {
+// MACSAN: define internal nonnull ptr @foo_ifunc() #[[#FOO_IFUNC:]] {
 
 // SAN: define dso_local noalias ptr @goo_ifunc() #[[#GOO_IFUNC:]] {
+// MACSAN: define noalias ptr @goo_ifunc() #[[#GOO_IFUNC:]] {
 
 // SAN-DAG: attributes #[[#FOO_IFUNC]] = {{{.*}} disable_sanitizer_instrumentation {{.*}}
+// MACSAN-DAG: attributes #[[#FOO_IFUNC]] = {{{.*}} disable_sanitizer_instrumentation {{.*}}
 
 // SAN-DAG: attributes #[[#GOO_IFUNC]] = {{{.*}} disable_sanitizer_instrumentation {{.*}}
+// MACSAN-DAG: attributes #[[#GOO_IFUNC]] = {{{.*}} disable_sanitizer_instrumentation {{.*}}

``````````

</details>


https://github.com/llvm/llvm-project/pull/73687