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[clang] Support __attribute__((ifunc(...))) on Darwin platforms
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. Reviewers: JDevlieghere, dmpolukhin, ahmedbougacha, tahonermann, echristo, MaskRay, erichkeane Reviewed By: MaskRay, echristo, ahmedbougacha Pull Request: #73687
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‎clang/include/clang/Basic/Attr.td

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -455,6 +455,9 @@ def TargetMicrosoftCXXABI : TargetArch<["x86", "x86_64", "arm", "thumb", "aarch6
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def TargetELF : TargetSpec {
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let ObjectFormats = ["ELF"];
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}
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def TargetELFOrMachO : TargetSpec {
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let ObjectFormats = ["ELF", "MachO"];
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}
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def TargetSupportsInitPriority : TargetSpec {
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let CustomCode = [{ !Target.getTriple().isOSzOS() }];
@@ -1665,7 +1668,7 @@ def IBOutletCollection : InheritableAttr {
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let Documentation = [Undocumented];
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}
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def IFunc : Attr, TargetSpecificAttr<TargetELF> {
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def IFunc : Attr, TargetSpecificAttr<TargetELFOrMachO> {
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let Spellings = [GCC<"ifunc">];
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let Args = [StringArgument<"Resolver">];
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let Subjects = SubjectList<[Function]>;

‎clang/include/clang/Basic/AttrDocs.td

Lines changed: 3 additions & 1 deletion
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@@ -5535,7 +5535,9 @@ considered inline.
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Not all targets support this attribute. ELF target support depends on both the
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linker and runtime linker, and is available in at least lld 4.0 and later,
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binutils 2.20.1 and later, glibc v2.11.1 and later, and FreeBSD 9.1 and later.
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Non-ELF targets currently do not support this attribute.
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Mach-O targets support it, but with slightly different semantics: the resolver
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is run at first call, instead of at load time by the runtime linker. Targets
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other than ELF and Mach-O currently do not support this attribute.
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}];
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}
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‎clang/test/CodeGen/attr-ifunc.c

Lines changed: 20 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1,6 +1,7 @@
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// RUN: %clang_cc1 -triple x86_64-windows -fsyntax-only -verify %s
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// RUN: %clang_cc1 -triple x86_64-linux -fsyntax-only -verify -emit-llvm-only -DCHECK_ALIASES %s
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// RUN: %clang_cc1 -triple x86_64-linux -fsyntax-only -verify -emit-llvm-only %s
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// RUN: %clang_cc1 -triple x86_64-apple-macosx -fsyntax-only -verify -emit-llvm-only %s
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#if defined(_WIN32)
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void foo(void) {}
@@ -36,6 +37,25 @@ void *f6_resolver(void) __attribute__((ifunc("f6_resolver_resolver")));
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void f6(void) __attribute__((ifunc("f6_resolver")));
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// expected-error@-1 {{ifunc must point to a defined function}}
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#elif defined(__APPLE__)
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// NOTE: aliases are not supported on Darwin, so the above tests are not relevant.
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#define STR2(X) #X
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#define STR(X) STR2(X)
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#define PREFIX STR(__USER_LABEL_PREFIX__)
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void f1a(void) __asm("f1");
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void f1a(void) {}
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// expected-note@-1 {{previous definition is here}}
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void f1(void) __attribute__((ifunc(PREFIX "f1_ifunc"))) __asm("f1");
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// expected-error@-1 {{definition with same mangled name '<U+0001>f1' as another definition}}
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void *f1_ifunc(void) { return 0; }
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void *f6_ifunc(int i);
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void __attribute__((ifunc(PREFIX "f6_ifunc"))) f6(void) {}
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// expected-error@-1 {{definition 'f6' cannot also be an ifunc}}
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#else
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void f1a(void) __asm("f1");
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void f1a(void) {}

‎clang/test/CodeGen/attr-ifunc.cpp

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,9 @@
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// RUN: %clang_cc1 -triple x86_64-linux -fsyntax-only -verify -emit-llvm-only %s
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// RUN: %clang_cc1 -triple x86_64-apple-macosx -fsyntax-only -verify -emit-llvm-only %s
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// RUN: %clang_cc1 -triple arm64-apple-macosx -fsyntax-only -verify -emit-llvm-only %s
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// RUN: not %clang_cc1 -triple x86_64-linux -emit-llvm-only -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
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// RUN: not %clang_cc1 -triple x86_64-apple-macosx -emit-llvm-only -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
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// RUN: not %clang_cc1 -triple arm64-apple-macosx -emit-llvm-only -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
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48
void *f1_ifunc(void) { return nullptr; }
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void f1(void) __attribute__((ifunc("f1_ifunc")));

‎clang/test/CodeGen/ifunc.c

Lines changed: 12 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3,6 +3,14 @@
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// RUN: %clang_cc1 -triple i386-unknown-linux-gnu -fsanitize=thread -O2 -emit-llvm -o - %s | FileCheck %s --check-prefix=SAN
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// RUN: %clang_cc1 -triple i386-unknown-linux-gnu -fsanitize=address -O2 -emit-llvm -o - %s | FileCheck %s --check-prefix=SAN
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// RUN: %clang_cc1 -triple i386-unknown-linux-gnu -fsanitize=memory -O2 -emit-llvm -o - %s | FileCheck %s --check-prefix=SAN
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// RUN: %clang_cc1 -triple arm64-apple-macosx -emit-llvm -o - %s | FileCheck %s
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// RUN: %clang_cc1 -triple x86_64-apple-macosx -emit-llvm -o - %s | FileCheck %s
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// RUN: %clang_cc1 -triple arm64-apple-macosx -O2 -emit-llvm -o - %s | FileCheck %s
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// RUN: %clang_cc1 -triple x86_64-apple-macosx -O2 -emit-llvm -o - %s | FileCheck %s
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// RUN: %clang_cc1 -triple arm64-apple-macosx -fsanitize=thread -O2 -emit-llvm -o - %s | FileCheck %s --check-prefix=MACSAN
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// RUN: %clang_cc1 -triple x86_64-apple-macosx -fsanitize=thread -O2 -emit-llvm -o - %s | FileCheck %s --check-prefix=MACSAN
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// RUN: %clang_cc1 -triple arm64-apple-macosx -fsanitize=address -O2 -emit-llvm -o - %s | FileCheck %s --check-prefix=MACSAN
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// RUN: %clang_cc1 -triple x86_64-apple-macosx -fsanitize=address -O2 -emit-llvm -o - %s | FileCheck %s --check-prefix=MACSAN
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int foo(int) __attribute__ ((ifunc("foo_ifunc")));
816

@@ -44,9 +52,13 @@ void* goo_ifunc(void) {
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// CHECK: call void @goo()
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4654
// SAN: define internal nonnull ptr @foo_ifunc() #[[#FOO_IFUNC:]] {
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// MACSAN: define internal nonnull ptr @foo_ifunc() #[[#FOO_IFUNC:]] {
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4857
// SAN: define dso_local noalias ptr @goo_ifunc() #[[#GOO_IFUNC:]] {
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// MACSAN: define noalias ptr @goo_ifunc() #[[#GOO_IFUNC:]] {
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5060
// SAN-DAG: attributes #[[#FOO_IFUNC]] = {{{.*}} disable_sanitizer_instrumentation {{.*}}
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// MACSAN-DAG: attributes #[[#FOO_IFUNC]] = {{{.*}} disable_sanitizer_instrumentation {{.*}}
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// SAN-DAG: attributes #[[#GOO_IFUNC]] = {{{.*}} disable_sanitizer_instrumentation {{.*}}
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// MACSAN-DAG: attributes #[[#GOO_IFUNC]] = {{{.*}} disable_sanitizer_instrumentation {{.*}}

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

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,6 @@
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// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -o - %s | FileCheck %s
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// RUN: %clang_cc1 -triple x86_64-apple-macosx -emit-llvm -o - %s | FileCheck %s
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// RUN: %clang_cc1 -triple arm64-apple-macosx -emit-llvm -o - %s | FileCheck %s
24

35
extern "C" {
46
__attribute__((used)) static void *resolve_foo() { return 0; }

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

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,9 @@
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// RUN: %clang_cc1 -emit-llvm-only -triple x86_64-linux-gnu -verify %s
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// RUN: %clang_cc1 -emit-llvm-only -triple x86_64-apple-macosx -verify %s
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// RUN: %clang_cc1 -emit-llvm-only -triple arm64-apple-macosx -verify %s
24
// RUN: not %clang_cc1 -triple x86_64-linux -emit-llvm-only -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
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// RUN: not %clang_cc1 -triple x86_64-apple-macosx -emit-llvm-only -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
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// RUN: not %clang_cc1 -triple arm64-apple-macosx -emit-llvm-only -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
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extern "C" {
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__attribute__((used)) static void *resolve_foo() { return 0; }

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

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

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