[clang] Support __attribute__((ifunc(...))) on Darwin platforms

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]>;

clang/include/clang/Basic/AttrDocs.td

@@ -5535,7 +5535,9 @@ 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.
+Mach-O 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 Mach-O currently do not support this attribute.
   }];
 }
 

clang/test/CodeGen/attr-ifunc.c

@@ -1,6 +1,7 @@
 // RUN: %clang_cc1 -triple x86_64-windows -fsyntax-only -verify %s
 // RUN: %clang_cc1 -triple x86_64-linux -fsyntax-only -verify -emit-llvm-only -DCHECK_ALIASES %s
 // RUN: %clang_cc1 -triple x86_64-linux -fsyntax-only -verify -emit-llvm-only %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx -fsyntax-only -verify -emit-llvm-only %s
 
 #if defined(_WIN32)
 void foo(void) {}
@@ -36,6 +37,25 @@ void *f6_resolver(void) __attribute__((ifunc("f6_resolver_resolver")));
 void f6(void) __attribute__((ifunc("f6_resolver")));
 // expected-error@-1 {{ifunc must point to a defined function}}
 
+#elif defined(__APPLE__)
+
+// NOTE: aliases are not supported on Darwin, so the above tests are not relevant.
+
+#define STR2(X) #X
+#define STR(X) STR2(X)
+#define PREFIX STR(__USER_LABEL_PREFIX__)
+
+void f1a(void) __asm("f1");
+void f1a(void) {}
+// expected-note@-1 {{previous definition is here}}
+void f1(void) __attribute__((ifunc(PREFIX "f1_ifunc"))) __asm("f1");
+// expected-error@-1 {{definition with same mangled name '<U+0001>f1' as another definition}}
+void *f1_ifunc(void) { return 0; }
+
+void *f6_ifunc(int i);
+void __attribute__((ifunc(PREFIX "f6_ifunc"))) f6(void) {}
+// expected-error@-1 {{definition 'f6' cannot also be an ifunc}}
+
 #else
 void f1a(void) __asm("f1");
 void f1a(void) {}

clang/test/CodeGen/attr-ifunc.cpp

@@ -1,5 +1,9 @@
 // RUN: %clang_cc1 -triple x86_64-linux -fsyntax-only -verify -emit-llvm-only %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx -fsyntax-only -verify -emit-llvm-only %s
+// RUN: %clang_cc1 -triple arm64-apple-macosx -fsyntax-only -verify -emit-llvm-only %s
 // RUN: not %clang_cc1 -triple x86_64-linux -emit-llvm-only -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
+// RUN: not %clang_cc1 -triple x86_64-apple-macosx -emit-llvm-only -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
+// RUN: not %clang_cc1 -triple arm64-apple-macosx -emit-llvm-only -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
 
 void *f1_ifunc(void) { return nullptr; }
 void f1(void) __attribute__((ifunc("f1_ifunc")));

clang/test/CodeGen/ifunc.c

@@ -3,6 +3,14 @@
 // 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 arm64-apple-macosx -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple arm64-apple-macosx -O2 -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 arm64-apple-macosx -fsanitize=thread -O2 -emit-llvm -o - %s | FileCheck %s --check-prefix=MACSAN
+// RUN: %clang_cc1 -triple x86_64-apple-macosx -fsanitize=thread -O2 -emit-llvm -o - %s | FileCheck %s --check-prefix=MACSAN
+// RUN: %clang_cc1 -triple arm64-apple-macosx -fsanitize=address -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 +52,13 @@ 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 {{.*}}

clang/test/CodeGenCXX/externc-ifunc-resolver.cpp

@@ -1,4 +1,6 @@
 // RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple arm64-apple-macosx -emit-llvm -o - %s | FileCheck %s
 
 extern "C" {
 __attribute__((used)) static void *resolve_foo() { return 0; }

clang/test/SemaCXX/externc-ifunc-resolver.cpp

@@ -1,5 +1,9 @@
 // RUN: %clang_cc1 -emit-llvm-only -triple x86_64-linux-gnu -verify %s
+// RUN: %clang_cc1 -emit-llvm-only -triple x86_64-apple-macosx -verify %s
+// RUN: %clang_cc1 -emit-llvm-only -triple arm64-apple-macosx -verify %s
 // RUN: not %clang_cc1 -triple x86_64-linux -emit-llvm-only -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
+// RUN: not %clang_cc1 -triple x86_64-apple-macosx -emit-llvm-only -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
+// RUN: not %clang_cc1 -triple arm64-apple-macosx -emit-llvm-only -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
 
 extern "C" {
 __attribute__((used)) static void *resolve_foo() { return 0; }

clang/test/SemaCXX/ifunc-has-attribute.cpp

@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -emit-llvm-only -triple x86_64-linux-gnu -verify %s -DSUPPORTED=1
+// RUN: %clang_cc1 -emit-llvm-only -triple x86_64-apple-macosx -verify %s -DSUPPORTED=1
+// RUN: %clang_cc1 -emit-llvm-only -triple arm64-apple-macosx -verify %s -DSUPPORTED=1
+// RUN: %clang_cc1 -emit-llvm-only -triple x86_64-pc-win32 -verify %s -DNOT_SUPPORTED=1
+
+// expected-no-diagnostics
+
+#if __has_attribute(ifunc)
+#  if NOT_SUPPORTED
+#    error "ifunc appears to be supported on this platform, but shouldn't be"
+#  endif
+#else
+#  if SUPPORTED
+#    error "ifunc should be supported on this platform, but isn't"
+#  endif
+#endif