nickdesaulniers updated this revision to Diff 443986.
nickdesaulniers added a comment.
- add more links to commit message as they come in
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D129572/new/
https://reviews.llvm.org/D129572
Files:
clang/docs/ReleaseNotes.rst
clang/include/clang/Basic/Attr.td
clang/include/clang/Basic/AttrDocs.td
clang/include/clang/Basic/CodeGenOptions.def
clang/include/clang/Driver/Options.td
clang/lib/CodeGen/CodeGenFunction.cpp
clang/lib/Driver/ToolChains/Clang.cpp
clang/lib/Frontend/CompilerInvocation.cpp
clang/lib/Sema/SemaDeclAttr.cpp
clang/test/CodeGen/attr-function-return.c
clang/test/CodeGen/attr-function-return.cpp
clang/test/Driver/mfunction-return.c
clang/test/Frontend/mfunction-return.c
clang/test/Misc/pragma-attribute-supported-attributes-list.test
clang/test/Sema/attr-function-return-unsupported-target.c
clang/test/Sema/attr-function-return.c
llvm/docs/LangRef.rst
llvm/include/llvm/Bitcode/LLVMBitCodes.h
llvm/include/llvm/IR/Attributes.td
llvm/include/llvm/Support/CodeGen.h
llvm/lib/Bitcode/Reader/BitcodeReader.cpp
llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
llvm/lib/Target/X86/CMakeLists.txt
llvm/lib/Target/X86/X86.h
llvm/lib/Target/X86/X86ReturnThunks.cpp
llvm/lib/Target/X86/X86TargetMachine.cpp
llvm/lib/Transforms/Utils/CodeExtractor.cpp
llvm/test/Bitcode/attributes.ll
llvm/test/CodeGen/X86/O0-pipeline.ll
llvm/test/CodeGen/X86/attr-function-return.ll
llvm/test/CodeGen/X86/attr-function-return.mir
llvm/test/CodeGen/X86/opt-pipeline.ll
llvm/test/Transforms/Inline/attributes.ll
Index: llvm/test/Transforms/Inline/attributes.ll
===================================================================
--- llvm/test/Transforms/Inline/attributes.ll
+++ llvm/test/Transforms/Inline/attributes.ll
@@ -600,6 +600,33 @@
; CHECK-NEXT: ret i32
}
+; Test that fn_ret_thunk_extern has no CompatRule; inlining is permitted.
+; Test that fn_ret_thunk_extern has no MergeRule; fn_ret_thunk_extern is not
+; propagated or dropped on the caller after inlining.
+define i32 @thunk_extern_callee() fn_ret_thunk_extern {
+; CHECK: @thunk_extern_callee() [[FNRETTHUNK_EXTERN:#[0-9]+]]
+ ret i32 42
+}
+
+define i32 @thunk_keep_caller() {
+; CHECK: @thunk_keep_caller() {
+; CHECK-NEXT: ret i32 42
+ %1 = call i32 @thunk_extern_callee()
+ ret i32 %1
+}
+
+define i32 @thunk_keep_callee() {
+; CHECK: @thunk_keep_callee() {
+ ret i32 42
+}
+
+define i32 @thunk_extern_caller() fn_ret_thunk_extern {
+; CHECK: @thunk_extern_caller() [[FNRETTHUNK_EXTERN]]
+; CHECK-NEXT: ret i32 42
+ %1 = call i32 @thunk_keep_callee()
+ ret i32 %1
+}
+
; CHECK: attributes [[SLH]] = { speculative_load_hardening }
; CHECK: attributes [[FPMAD_FALSE]] = { "less-precise-fpmad"="false" }
; CHECK: attributes [[FPMAD_TRUE]] = { "less-precise-fpmad"="true" }
@@ -614,3 +641,4 @@
; CHECK: attributes [[NO_SIGNED_ZEROS_FPMATH_TRUE]] = { "no-signed-zeros-fp-math"="true" }
; CHECK: attributes [[UNSAFE_FPMATH_FALSE]] = { "unsafe-fp-math"="false" }
; CHECK: attributes [[UNSAFE_FPMATH_TRUE]] = { "unsafe-fp-math"="true" }
+; CHECK: attributes [[FNRETTHUNK_EXTERN]] = { fn_ret_thunk_extern }
Index: llvm/test/CodeGen/X86/opt-pipeline.ll
===================================================================
--- llvm/test/CodeGen/X86/opt-pipeline.ll
+++ llvm/test/CodeGen/X86/opt-pipeline.ll
@@ -204,6 +204,7 @@
; CHECK-NEXT: Live DEBUG_VALUE analysis
; CHECK-NEXT: X86 Speculative Execution Side Effect Suppression
; CHECK-NEXT: X86 Indirect Thunks
+; CHECK-NEXT: X86 Return Thunks
; CHECK-NEXT: Check CFA info and insert CFI instructions if needed
; CHECK-NEXT: X86 Load Value Injection (LVI) Ret-Hardening
; CHECK-NEXT: Pseudo Probe Inserter
Index: llvm/test/CodeGen/X86/attr-function-return.mir
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/X86/attr-function-return.mir
@@ -0,0 +1,62 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc --mtriple=x86_64-linux-gnu -run-pass=x86-return-thunks \
+# RUN: -verify-machineinstrs %s -o - | FileCheck %s
+--- |
+ ; ModuleID = 'y.ll'
+ source_filename = "y.ll"
+ target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+
+ define void @x() #0 {
+ ret void
+ }
+
+ attributes #0 = { fn_ret_thunk_extern }
+
+...
+---
+name: x
+alignment: 16
+exposesReturnsTwice: false
+legalized: false
+regBankSelected: false
+selected: false
+failedISel: false
+tracksRegLiveness: true
+hasWinCFI: false
+failsVerification: false
+tracksDebugUserValues: true
+registers: []
+liveins: []
+frameInfo:
+ isFrameAddressTaken: false
+ isReturnAddressTaken: false
+ hasStackMap: false
+ hasPatchPoint: false
+ stackSize: 0
+ offsetAdjustment: 0
+ maxAlignment: 1
+ adjustsStack: false
+ hasCalls: false
+ stackProtector: ''
+ maxCallFrameSize: 0
+ cvBytesOfCalleeSavedRegisters: 0
+ hasOpaqueSPAdjustment: false
+ hasVAStart: false
+ hasMustTailInVarArgFunc: false
+ hasTailCall: false
+ localFrameSize: 0
+ savePoint: ''
+ restorePoint: ''
+fixedStack: []
+stack: []
+callSites: []
+debugValueSubstitutions: []
+constants: []
+machineFunctionInfo: {}
+body: |
+ bb.0 (%ir-block.0):
+ ; CHECK-LABEL: name: x
+ ; CHECK: TAILJMPd &__x86_return_thunk, implicit $esp, implicit $ssp
+ RET64
+
+...
Index: llvm/test/CodeGen/X86/attr-function-return.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/X86/attr-function-return.ll
@@ -0,0 +1,11 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc --mtriple=i386-linux-gnu %s -o - -verify-machineinstrs \
+; RUN: | FileCheck %s
+; RUN: llc --mtriple=x86_64-linux-gnu %s -o - -verify-machineinstrs \
+; RUN: | FileCheck %s
+define void @x() fn_ret_thunk_extern {
+; CHECK-LABEL: x:
+; CHECK: # %bb.0:
+; CHECK-NEXT: jmp __x86_return_thunk
+ ret void
+}
Index: llvm/test/CodeGen/X86/O0-pipeline.ll
===================================================================
--- llvm/test/CodeGen/X86/O0-pipeline.ll
+++ llvm/test/CodeGen/X86/O0-pipeline.ll
@@ -71,8 +71,9 @@
; CHECK-NEXT: Live DEBUG_VALUE analysis
; CHECK-NEXT: X86 Speculative Execution Side Effect Suppression
; CHECK-NEXT: X86 Indirect Thunks
+; CHECK-NEXT: X86 Return Thunks
; CHECK-NEXT: Check CFA info and insert CFI instructions if needed
-; CHECK-NEXT: X86 Load Value Injection (LVI) Ret-Hardening
+; CHECK-NEXT: X86 Load Value Injection (LVI) Ret-Hardening
; CHECK-NEXT: Pseudo Probe Inserter
; CHECK-NEXT: Lazy Machine Block Frequency Analysis
; CHECK-NEXT: Machine Optimization Remark Emitter
Index: llvm/test/Bitcode/attributes.ll
===================================================================
--- llvm/test/Bitcode/attributes.ll
+++ llvm/test/Bitcode/attributes.ll
@@ -532,6 +532,9 @@
ret void;
}
+; CHECK: define void @f87() [[FNRETTHUNKEXTERN:#[0-9]+]]
+define void @f87() fn_ret_thunk_extern { ret void }
+
; CHECK: attributes #0 = { noreturn }
; CHECK: attributes #1 = { nounwind }
; CHECK: attributes #2 = { readnone }
@@ -585,4 +588,5 @@
; CHECK: attributes #50 = { disable_sanitizer_instrumentation }
; CHECK: attributes #51 = { uwtable(sync) }
; CHECK: attributes #52 = { nosanitize_bounds }
+; CHECK: attributes [[FNRETTHUNKEXTERN]] = { fn_ret_thunk_extern }
; CHECK: attributes #[[NOBUILTIN]] = { nobuiltin }
Index: llvm/lib/Transforms/Utils/CodeExtractor.cpp
===================================================================
--- llvm/lib/Transforms/Utils/CodeExtractor.cpp
+++ llvm/lib/Transforms/Utils/CodeExtractor.cpp
@@ -927,6 +927,7 @@
case Attribute::AlwaysInline:
case Attribute::Cold:
case Attribute::DisableSanitizerInstrumentation:
+ case Attribute::FnRetThunkExtern:
case Attribute::Hot:
case Attribute::NoRecurse:
case Attribute::InlineHint:
Index: llvm/lib/Target/X86/X86TargetMachine.cpp
===================================================================
--- llvm/lib/Target/X86/X86TargetMachine.cpp
+++ llvm/lib/Target/X86/X86TargetMachine.cpp
@@ -100,6 +100,7 @@
initializeX86OptimizeLEAPassPass(PR);
initializeX86PartialReductionPass(PR);
initializePseudoProbeInserterPass(PR);
+ initializeX86ReturnThunksPass(PR);
}
static std::unique_ptr<TargetLoweringObjectFile> createTLOF(const Triple &TT) {
@@ -575,6 +576,7 @@
// hand inspection of the codegen output.
addPass(createX86SpeculativeExecutionSideEffectSuppression());
addPass(createX86IndirectThunksPass());
+ addPass(createX86ReturnThunksPass());
// Insert extra int3 instructions after trailing call instructions to avoid
// issues in the unwinder.
Index: llvm/lib/Target/X86/X86ReturnThunks.cpp
===================================================================
--- /dev/null
+++ llvm/lib/Target/X86/X86ReturnThunks.cpp
@@ -0,0 +1,92 @@
+//==- X86ReturnThunks.cpp - Replace rets with thunks or inline thunks --=//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+/// \file
+///
+/// Pass that replaces ret instructions with a jmp to __x86_return_thunk.
+///
+/// This corresponds to -mfunction-return=thunk-extern or
+/// __attribute__((function_return("thunk-extern").
+///
+/// This pass is a minimal implementation necessary to help mitigate
+/// RetBleed for the Linux kernel.
+///
+/// Should support for thunk or thunk-inline be necessary in the future, then
+/// this pass should be combined with x86-retpoline-thunks which already has
+/// machinery to emit thunks. Until then, YAGNI.
+///
+/// This pass is very similar to x86-lvi-ret.
+///
+//===----------------------------------------------------------------------===//
+
+#include "X86.h"
+#include "X86InstrInfo.h"
+#include "X86Subtarget.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/Triple.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/MC/MCInstrDesc.h"
+#include "llvm/Support/Debug.h"
+
+using namespace llvm;
+
+#define PASS_KEY "x86-return-thunks"
+#define DEBUG_TYPE PASS_KEY
+
+struct X86ReturnThunks final : public MachineFunctionPass {
+ static char ID;
+ X86ReturnThunks() : MachineFunctionPass(ID) {}
+ StringRef getPassName() const override { return "X86 Return Thunks"; }
+ bool runOnMachineFunction(MachineFunction &MF) override;
+};
+
+char X86ReturnThunks::ID = 0;
+
+bool X86ReturnThunks::runOnMachineFunction(MachineFunction &MF) {
+ LLVM_DEBUG(dbgs() << getPassName() << "\n");
+
+ bool Modified = false;
+
+ if (!MF.getFunction().hasFnAttribute(llvm::Attribute::FnRetThunkExtern))
+ return Modified;
+
+ StringRef ThunkName = "__x86_return_thunk";
+ if (MF.getFunction().getName() == ThunkName)
+ return Modified;
+
+ const auto &ST = MF.getSubtarget<X86Subtarget>();
+ const bool Is64Bit = ST.getTargetTriple().getArch() == Triple::x86_64;
+ const unsigned RetOpc = Is64Bit ? X86::RET64 : X86::RET32;
+ SmallVector<MachineInstr *, 16> Rets;
+
+ for (MachineBasicBlock &MBB : MF)
+ for (MachineInstr &Term : MBB.terminators())
+ if (Term.getOpcode() == RetOpc)
+ Rets.push_back(&Term);
+
+ const MCInstrDesc &JMP = ST.getInstrInfo()->get(X86::TAILJMPd);
+
+ for (MachineInstr *Ret : Rets) {
+ BuildMI(Ret->getParent(), Ret->getDebugLoc(), JMP)
+ .addExternalSymbol(ThunkName.data());
+ Ret->eraseFromParent();
+ Modified = true;
+ }
+
+ return Modified;
+}
+
+INITIALIZE_PASS(X86ReturnThunks, PASS_KEY, "X86 Return Thunks", false, false)
+
+FunctionPass *llvm::createX86ReturnThunksPass() {
+ return new X86ReturnThunks();
+}
Index: llvm/lib/Target/X86/X86.h
===================================================================
--- llvm/lib/Target/X86/X86.h
+++ llvm/lib/Target/X86/X86.h
@@ -132,6 +132,9 @@
/// This pass creates the thunks for the retpoline feature.
FunctionPass *createX86IndirectThunksPass();
+/// This pass replaces ret instructions with jmp's to __x86_return thunk.
+FunctionPass *createX86ReturnThunksPass();
+
/// This pass ensures instructions featuring a memory operand
/// have distinctive <LineNumber, Discriminator> (with respect to eachother)
FunctionPass *createX86DiscriminateMemOpsPass();
@@ -185,6 +188,7 @@
void initializeX86PreAMXConfigPassPass(PassRegistry &);
void initializeX86LowerTileCopyPass(PassRegistry &);
void initializeX86LowerAMXIntrinsicsLegacyPassPass(PassRegistry &);
+void initializeX86ReturnThunksPass(PassRegistry &);
namespace X86AS {
enum : unsigned {
Index: llvm/lib/Target/X86/CMakeLists.txt
===================================================================
--- llvm/lib/Target/X86/CMakeLists.txt
+++ llvm/lib/Target/X86/CMakeLists.txt
@@ -75,6 +75,7 @@
X86PartialReduction.cpp
X86RegisterBankInfo.cpp
X86RegisterInfo.cpp
+ X86ReturnThunks.cpp
X86SelectionDAGInfo.cpp
X86ShuffleDecodeConstantPool.cpp
X86SpeculativeLoadHardening.cpp
Index: llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
===================================================================
--- llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -634,6 +634,8 @@
return bitc::ATTR_KIND_COLD;
case Attribute::DisableSanitizerInstrumentation:
return bitc::ATTR_KIND_DISABLE_SANITIZER_INSTRUMENTATION;
+ case Attribute::FnRetThunkExtern:
+ return bitc::ATTR_KIND_FNRETTHUNK_EXTERN;
case Attribute::Hot:
return bitc::ATTR_KIND_HOT;
case Attribute::ElementType:
Index: llvm/lib/Bitcode/Reader/BitcodeReader.cpp
===================================================================
--- llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -1855,6 +1855,8 @@
return Attribute::DisableSanitizerInstrumentation;
case bitc::ATTR_KIND_ELEMENTTYPE:
return Attribute::ElementType;
+ case bitc::ATTR_KIND_FNRETTHUNK_EXTERN:
+ return Attribute::FnRetThunkExtern;
case bitc::ATTR_KIND_INACCESSIBLEMEM_ONLY:
return Attribute::InaccessibleMemOnly;
case bitc::ATTR_KIND_INACCESSIBLEMEM_OR_ARGMEMONLY:
Index: llvm/include/llvm/Support/CodeGen.h
===================================================================
--- llvm/include/llvm/Support/CodeGen.h
+++ llvm/include/llvm/Support/CodeGen.h
@@ -103,6 +103,13 @@
Async = 2, ///< "Asynchronous" unwind tables (instr precise)
Default = 2,
};
+
+ enum class FunctionReturnThunksKind : unsigned int {
+ Keep = 0, ///< No function return thunk.
+ Extern = 1, ///< Replace returns with jump to thunk, don't emit thunk.
+ Invalid = 2, ///< Not used.
+ };
+
} // namespace llvm
#endif
Index: llvm/include/llvm/IR/Attributes.td
===================================================================
--- llvm/include/llvm/IR/Attributes.td
+++ llvm/include/llvm/IR/Attributes.td
@@ -102,6 +102,10 @@
/// Provide pointer element type to intrinsic.
def ElementType : TypeAttr<"elementtype", [ParamAttr]>;
+/// Whether to keep return instructions, or replace with a jump to an external
+/// symbol.
+def FnRetThunkExtern : EnumAttr<"fn_ret_thunk_extern", [FnAttr]>;
+
/// Function may only access memory that is inaccessible from IR.
def InaccessibleMemOnly : EnumAttr<"inaccessiblememonly", [FnAttr]>;
Index: llvm/include/llvm/Bitcode/LLVMBitCodes.h
===================================================================
--- llvm/include/llvm/Bitcode/LLVMBitCodes.h
+++ llvm/include/llvm/Bitcode/LLVMBitCodes.h
@@ -688,6 +688,7 @@
ATTR_KIND_ALLOCATED_POINTER = 81,
ATTR_KIND_ALLOC_KIND = 82,
ATTR_KIND_PRESPLIT_COROUTINE = 83,
+ ATTR_KIND_FNRETTHUNK_EXTERN = 84,
};
enum ComdatSelectionKindCodes {
Index: llvm/docs/LangRef.rst
===================================================================
--- llvm/docs/LangRef.rst
+++ llvm/docs/LangRef.rst
@@ -1678,6 +1678,10 @@
Front ends can provide optional ``srcloc`` metadata nodes on call sites of
such callees to attach information about where in the source language such a
call came from. A string value can be provided as a note.
+``fn_ret_thunk_extern``
+ This attribute tells the code generator that returns from functions should
+ be replaced with jumps to externally-defined architecture-specific symbols.
+ For X86, this symbol's identifier is ``__x86_return_thunk``.
``"frame-pointer"``
This attribute tells the code generator whether the function
should keep the frame pointer. The code generator may emit the frame pointer
Index: clang/test/Sema/attr-function-return.c
===================================================================
--- /dev/null
+++ clang/test/Sema/attr-function-return.c
@@ -0,0 +1,23 @@
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -verify %s
+
+__attribute__((function_return("keep"))) void x(void) {}
+
+// expected-warning@+1 {{'function_return' attribute argument not supported: thunk}}
+__attribute__((function_return("thunk"))) void y(void) {}
+
+// expected-warning@+1 {{'function_return' attribute argument not supported: thunk-inline}}
+__attribute__((function_return("thunk-inline"))) void z(void) {}
+
+__attribute__((function_return("thunk-extern"))) void w(void) {}
+
+// expected-warning@+1 {{'function_return' attribute argument not supported: invalid}}
+__attribute__((function_return("invalid"))) void v(void) {}
+
+// expected-error@+1 {{'function_return' attribute requires a string}}
+__attribute__((function_return(5))) void a(void) {}
+
+// expected-error@+1 {{'function_return' attribute takes one argument}}
+__attribute__((function_return)) void b(void) {}
+
+// expected-warning@+1 {{'function_return' attribute only applies to functions}}
+__attribute__((function_return)) int c;
Index: clang/test/Sema/attr-function-return-unsupported-target.c
===================================================================
--- /dev/null
+++ clang/test/Sema/attr-function-return-unsupported-target.c
@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -triple s390x-linux-gnu -fsyntax-only -verify %s
+
+// expected-warning@+1 {{unknown attribute 'function_return' ignored}}
+__attribute__((function_return("keep"))) void x(void) {}
+
+// expected-warning@+1 {{unknown attribute 'function_return' ignored}}
+__attribute__((function_return("thunk"))) void y(void) {}
+
+// expected-warning@+1 {{unknown attribute 'function_return' ignored}}
+__attribute__((function_return("thunk-inline"))) void z(void) {}
+
+// expected-warning@+1 {{unknown attribute 'function_return' ignored}}
+__attribute__((function_return("thunk-extern"))) void w(void) {}
+
+// expected-warning@+1 {{unknown attribute 'function_return' ignored}}
+__attribute__((function_return("invalid"))) void v(void) {}
Index: clang/test/Misc/pragma-attribute-supported-attributes-list.test
===================================================================
--- clang/test/Misc/pragma-attribute-supported-attributes-list.test
+++ clang/test/Misc/pragma-attribute-supported-attributes-list.test
@@ -69,6 +69,7 @@
// CHECK-NEXT: ExternalSourceSymbol ((SubjectMatchRule_record, SubjectMatchRule_enum, SubjectMatchRule_enum_constant, SubjectMatchRule_field, SubjectMatchRule_function, SubjectMatchRule_namespace, SubjectMatchRule_objc_category, SubjectMatchRule_objc_implementation, SubjectMatchRule_objc_interface, SubjectMatchRule_objc_method, SubjectMatchRule_objc_property, SubjectMatchRule_objc_protocol, SubjectMatchRule_record, SubjectMatchRule_type_alias, SubjectMatchRule_variable))
// CHECK-NEXT: FlagEnum (SubjectMatchRule_enum)
// CHECK-NEXT: Flatten (SubjectMatchRule_function)
+// CHECK-NEXT: FunctionReturnThunks (SubjectMatchRule_function)
// CHECK-NEXT: GNUInline (SubjectMatchRule_function)
// CHECK-NEXT: HIPManaged (SubjectMatchRule_variable)
// CHECK-NEXT: Hot (SubjectMatchRule_function)
Index: clang/test/Frontend/mfunction-return.c
===================================================================
--- /dev/null
+++ clang/test/Frontend/mfunction-return.c
@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -mfunction-return=keep -triple x86_64-linux-gnu %s
+// RUN: %clang_cc1 -mfunction-return=thunk-extern -triple x86_64-linux-gnu %s
+
+// RUN: not %clang_cc1 -mfunction-return=thunk -triple x86_64-linux-gnu %s 2>&1 \
+// RUN: | FileCheck --check-prefix=CHECK-THUNK %s
+// RUN: not %clang_cc1 -mfunction-return=thunk-inline -triple x86_64-linux-gnu %s 2>&1 \
+// RUN: | FileCheck --check-prefix=CHECK-INLINE %s
+// RUN: not %clang_cc1 -mfunction-return=invalid -triple x86_64-linux-gnu %s 2>&1 \
+// RUN: | FileCheck --check-prefix=CHECK-INVALID %s
+// RUN: not %clang_cc1 -mfunction-return=thunk-extern -triple s390x-linux-gnu %s 2>&1 \
+// RUN: | FileCheck --check-prefix=CHECK-TARGET %s
+// RUN: not %clang_cc1 -mfunction-return=thunk-extern -mcmodel=large \
+// RUN: -triple x86_64-linux-gnu %s 2>&1 \
+// RUN: | FileCheck --check-prefix=CHECK-LARGE %s
+
+// CHECK-THUNK: error: invalid value 'thunk' in '-mfunction-return=thunk'
+// CHECK-INLINE: error: invalid value 'thunk-inline' in '-mfunction-return=thunk-inline'
+// CHECK-INVALID: error: invalid value 'invalid' in '-mfunction-return=invalid'
+// CHECK-TARGET: error: invalid argument '-mfunction-return=' not allowed with 's390x-unknown-linux-gnu'
+// CHECK-LARGE: error: invalid argument '-mfunction-return=thunk-extern' not allowed with '-mcmodel=large'
Index: clang/test/Driver/mfunction-return.c
===================================================================
--- /dev/null
+++ clang/test/Driver/mfunction-return.c
@@ -0,0 +1,22 @@
+// RUN: %clang -mfunction-return= -### %s 2>&1 \
+// RUN: | FileCheck --check-prefix=CHECK-VALID %s
+// RUN: not %clang -mfunction-return -### %s 2>&1 \
+// RUN: | FileCheck --check-prefix=CHECK-INVALID %s
+
+// RUN: %clang -mfunction-return=keep -### %s 2>&1 \
+// RUN: | FileCheck --check-prefix=CHECK-KEEP %s
+// RUN: %clang -mfunction-return=thunk-extern -### %s 2>&1 \
+// RUN: | FileCheck --check-prefix=CHECK-EXTERN %s
+
+// RUN: %clang -mfunction-return=keep -mfunction-return=thunk-extern -### %s 2>&1 \
+// RUN: | FileCheck --check-prefix=CHECK-EXTERN %s
+// RUN: %clang -mfunction-return=thunk-extern -mfunction-return=keep -### %s 2>&1 \
+// RUN: | FileCheck --check-prefix=CHECK-KEEP %s
+
+// CHECK-VALID: "-mfunction-return="
+// CHECK-INVALID: error: unknown argument: '-mfunction-return'
+
+// CHECK-KEEP: "-mfunction-return=keep"
+// CHECK-KEEP-NOT: "-mfunction-return=thunk-extern"
+// CHECK-EXTERN: "-mfunction-return=thunk-extern"
+// CHECK-EXTERN-NOT: "-mfunction-return=keep"
Index: clang/test/CodeGen/attr-function-return.cpp
===================================================================
--- /dev/null
+++ clang/test/CodeGen/attr-function-return.cpp
@@ -0,0 +1,52 @@
+// RUN: %clang_cc1 -triple x86_64-linux-gnu %s -emit-llvm -o - \
+// RUN: | FileCheck %s --check-prefixes=CHECK,CHECK-NOM
+// RUN: %clang_cc1 -triple x86_64-linux-gnu %s -emit-llvm -o - \
+// RUN: -mfunction-return=keep | FileCheck %s \
+// RUN: --check-prefixes=CHECK,CHECK-KEEP
+// RUN: %clang_cc1 -triple x86_64-linux-gnu %s -emit-llvm -o - \
+// RUN: -mfunction-return=thunk-extern | FileCheck %s \
+// RUN: --check-prefixes=CHECK,CHECK-EXTERN
+
+int foo(void) {
+ // CHECK: @"_ZZ3foovENK3$_0clEv"({{.*}}) [[NOATTR:#[0-9]+]]
+ return []() {
+ return 42;
+ }();
+}
+int bar(void) {
+ // CHECK: @"_ZZ3barvENK3$_1clEv"({{.*}}) [[EXTERN:#[0-9]+]]
+ return []() __attribute__((function_return("thunk-extern"))) {
+ return 42;
+ }
+ ();
+}
+int baz(void) {
+ // CHECK: @"_ZZ3bazvENK3$_2clEv"({{.*}}) [[KEEP:#[0-9]+]]
+ return []() __attribute__((function_return("keep"))) {
+ return 42;
+ }
+ ();
+}
+
+class Foo {
+public:
+ // CHECK: @_ZN3Foo3fooEv({{.*}}) [[EXTERN]]
+ __attribute__((function_return("thunk-extern"))) int foo() { return 42; }
+};
+
+int quux() {
+ Foo my_foo;
+ return my_foo.foo();
+}
+
+// CHECK: @extern_c() [[EXTERN]]
+extern "C" __attribute__((function_return("thunk-extern"))) void extern_c() {}
+extern "C" {
+// CHECK: @extern_c2() [[EXTERN]]
+__attribute__((function_return("thunk-extern"))) void extern_c2() {}
+}
+
+// CHECK-NOM-NOT: [[NOATTR]] = {{.*}}fn_ret_thunk_extern
+// CHECK-KEEP-NOT: [[NOATTR]] = {{.*}}fn_ret_thunk_extern
+// CHECK-KEEP-NOT: [[KEEP]] = {{.*}}fn_ret_thunk_extern
+// CHECK-EXTERN: [[EXTERN]] = {{.*}}fn_ret_thunk_extern
Index: clang/test/CodeGen/attr-function-return.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/attr-function-return.c
@@ -0,0 +1,96 @@
+// RUN: %clang_cc1 -std=gnu2x -triple x86_64-linux-gnu %s -emit-llvm -o - \
+// RUN: | FileCheck %s --check-prefixes=CHECK,CHECK-NOM
+// RUN: %clang_cc1 -std=gnu2x -triple x86_64-linux-gnu %s -emit-llvm -o - \
+// RUN: -mfunction-return=keep | FileCheck %s \
+// RUN: --check-prefixes=CHECK,CHECK-KEEP
+// RUN: %clang_cc1 -std=gnu2x -triple x86_64-linux-gnu %s -emit-llvm -o - \
+// RUN: -mfunction-return=thunk-extern | FileCheck %s \
+// RUN: --check-prefixes=CHECK,CHECK-EXTERN
+
+#if !__has_attribute(function_return)
+#error "missing attribute support for function_return"
+#endif
+
+// CHECK: @keep() [[KEEP:#[0-9]+]]
+__attribute__((function_return("keep"))) void keep(void) {}
+
+// CHECK: @keep2() [[KEEP:#[0-9]+]]
+[[gnu::function_return("keep")]] void keep2(void) {}
+
+// CHECK: @thunk_extern() [[EXTERN:#[0-9]+]]
+__attribute__((function_return("thunk-extern"))) void thunk_extern(void) {}
+
+// CHECK: @thunk_extern2() [[EXTERN:#[0-9]+]]
+[[gnu::function_return("thunk-extern")]] void thunk_extern2(void) {}
+
+// CHECK: @double_thunk_keep() [[KEEP]]
+// clang-format off
+__attribute__((function_return("thunk-extern")))
+__attribute__((function_return("keep")))
+void double_thunk_keep(void) {}
+
+// CHECK: @double_thunk_keep2() [[KEEP]]
+[[gnu::function_return("thunk-extern")]][[gnu::function_return("keep")]]
+void double_thunk_keep2(void) {}
+
+// CHECK: @double_keep_thunk() [[EXTERN]]
+__attribute__((function_return("keep")))
+__attribute__((function_return("thunk-extern")))
+void double_keep_thunk(void) {}
+
+// CHECK: @double_keep_thunk2() [[EXTERN]]
+[[gnu::function_return("thunk-keep")]][[gnu::function_return("thunk-extern")]]
+void double_keep_thunk2(void) {}
+
+// CHECK: @thunk_keep() [[KEEP]]
+__attribute__((function_return("thunk-extern"), function_return("keep")))
+void thunk_keep(void) {}
+
+// CHECK: @thunk_keep2() [[KEEP]]
+[[gnu::function_return("thunk-extern"), gnu::function_return("keep")]]
+void thunk_keep2(void) {}
+
+// CHECK: @keep_thunk() [[EXTERN]]
+__attribute__((function_return("keep"), function_return("thunk-extern")))
+void keep_thunk(void) {}
+
+// CHECK: @keep_thunk2() [[EXTERN]]
+[[gnu::function_return("keep"), gnu::function_return("thunk-extern")]]
+void keep_thunk2(void) {}
+// clang-format on
+
+void undef(void);
+// CHECK: @undef() [[KEEP]]
+__attribute__((function_return("keep"))) void undef(void) {}
+
+void undef2(void);
+// CHECK: @undef2() [[EXTERN]]
+__attribute__((function_return("thunk-extern"))) void undef2(void) {}
+
+__attribute__((function_return("thunk-extern"))) void change_def(void);
+// CHECK: @change_def() [[KEEP]]
+__attribute__((function_return("keep"))) void change_def(void) {}
+
+__attribute__((function_return("keep"))) void change_def2(void);
+// CHECK: @change_def2() [[EXTERN]]
+__attribute__((function_return("thunk-extern"))) void change_def2(void) {}
+
+__attribute__((function_return("thunk-extern"))) void change_def3(void);
+// CHECK: @change_def3() [[KEEP]]
+[[gnu::function_return("keep")]] void change_def3(void) {}
+
+[[gnu::function_return("keep")]] void change_def4(void);
+// CHECK: @change_def4() [[EXTERN]]
+__attribute__((function_return("thunk-extern"))) void change_def4(void) {}
+
+// When there is no -mfunction-return= flag set (NOM) or it's set to keep,
+// we don't emit anything into the IR for unattributed functions.
+
+// CHECK-NOM: @no_attrs() [[NOATTR:#[0-9]+]]
+// CHECK-KEEP: @no_attrs() [[NOATTR:#[0-9]+]]
+// CHECK-EXTERN: @no_attrs() [[EXTERN]]
+void no_attrs(void) {}
+
+// CHECK-NOM-NOT: [[NOATTR]] = {{.*}}fn_ret_thunk_extern
+// CHECK-KEEP-NOT: [[NOATTR]] = {{.*}}fn_ret_thunk_extern
+// CHECK: [[EXTERN]] = {{.*}}fn_ret_thunk_extern
Index: clang/lib/Sema/SemaDeclAttr.cpp
===================================================================
--- clang/lib/Sema/SemaDeclAttr.cpp
+++ clang/lib/Sema/SemaDeclAttr.cpp
@@ -8000,6 +8000,26 @@
D->addAttr(ZeroCallUsedRegsAttr::Create(S.Context, Kind, AL));
}
+static void handleFunctionReturnThunksAttr(Sema &S, Decl *D,
+ const ParsedAttr &AL) {
+ StringRef KindStr;
+ SourceLocation LiteralLoc;
+ if (!S.checkStringLiteralArgumentAttr(AL, 0, KindStr, &LiteralLoc))
+ return;
+
+ FunctionReturnThunksAttr::Kind Kind;
+ if (!FunctionReturnThunksAttr::ConvertStrToKind(KindStr, Kind)) {
+ S.Diag(LiteralLoc, diag::warn_attribute_type_not_supported)
+ << AL << KindStr;
+ return;
+ }
+ // FIXME: it would be good to better handle attribute merging rather than
+ // silently replacing the existing attribute, so long as it does not break
+ // the expected codegen tests.
+ D->dropAttr<FunctionReturnThunksAttr>();
+ D->addAttr(FunctionReturnThunksAttr::Create(S.Context, Kind, AL));
+}
+
static void handleSYCLKernelAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
// The 'sycl_kernel' attribute applies only to function templates.
const auto *FD = cast<FunctionDecl>(D);
@@ -8866,6 +8886,9 @@
case ParsedAttr::AT_ZeroCallUsedRegs:
handleZeroCallUsedRegsAttr(S, D, AL);
break;
+ case ParsedAttr::AT_FunctionReturnThunks:
+ handleFunctionReturnThunksAttr(S, D, AL);
+ break;
// Microsoft attributes:
case ParsedAttr::AT_LayoutVersion:
Index: clang/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- clang/lib/Frontend/CompilerInvocation.cpp
+++ clang/lib/Frontend/CompilerInvocation.cpp
@@ -1485,6 +1485,9 @@
if (Opts.IBTSeal)
GenerateArg(Args, OPT_mibt_seal, SA);
+ if (Opts.FunctionReturnThunks)
+ GenerateArg(Args, OPT_mfunction_return_EQ, "thunk-extern", SA);
+
for (const auto &F : Opts.LinkBitcodeFiles) {
bool Builtint = F.LinkFlags == llvm::Linker::Flags::LinkOnlyNeeded &&
F.PropagateAttrs && F.Internalize;
@@ -1825,6 +1828,27 @@
Diags.Report(diag::err_drv_invalid_value) << A->getAsString(Args) << Name;
}
+ if (const Arg *A = Args.getLastArg(OPT_mfunction_return_EQ)) {
+ auto Val = llvm::StringSwitch<llvm::FunctionReturnThunksKind>(A->getValue())
+ .Case("keep", llvm::FunctionReturnThunksKind::Keep)
+ .Case("thunk-extern", llvm::FunctionReturnThunksKind::Extern)
+ .Default(llvm::FunctionReturnThunksKind::Invalid);
+ // SystemZ might want to add support for "expolines."
+ if (!T.isX86())
+ Diags.Report(diag::err_drv_argument_not_allowed_with)
+ << A->getSpelling() << T.getTriple();
+ else if (Val == llvm::FunctionReturnThunksKind::Invalid)
+ Diags.Report(diag::err_drv_invalid_value)
+ << A->getAsString(Args) << A->getValue();
+ else if (Val == llvm::FunctionReturnThunksKind::Extern &&
+ Args.getLastArgValue(OPT_mcmodel_EQ).equals("large"))
+ Diags.Report(diag::err_drv_argument_not_allowed_with)
+ << A->getAsString(Args)
+ << Args.getLastArg(OPT_mcmodel_EQ)->getAsString(Args);
+ else
+ Opts.FunctionReturnThunks = static_cast<unsigned>(Val);
+ }
+
if (Opts.PrepareForLTO && Args.hasArg(OPT_mibt_seal))
Opts.IBTSeal = 1;
Index: clang/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -6344,6 +6344,10 @@
if (IsUsingLTO)
Args.AddLastArg(CmdArgs, options::OPT_mibt_seal);
+ if (Arg *A = Args.getLastArg(options::OPT_mfunction_return_EQ))
+ CmdArgs.push_back(
+ Args.MakeArgString(Twine("-mfunction-return=") + A->getValue()));
+
// Forward -f options with positive and negative forms; we translate these by
// hand. Do not propagate PGO options to the GPU-side compilations as the
// profile info is for the host-side compilation only.
Index: clang/lib/CodeGen/CodeGenFunction.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenFunction.cpp
+++ clang/lib/CodeGen/CodeGenFunction.cpp
@@ -898,6 +898,20 @@
if (D && D->hasAttr<NoProfileFunctionAttr>())
Fn->addFnAttr(llvm::Attribute::NoProfile);
+ if (D) {
+ // Function attributes take precedence over command line flags.
+ if (auto *A = D->getAttr<FunctionReturnThunksAttr>()) {
+ switch (A->getThunkType()) {
+ case FunctionReturnThunksAttr::Kind::Keep:
+ break;
+ case FunctionReturnThunksAttr::Kind::Extern:
+ Fn->addFnAttr(llvm::Attribute::FnRetThunkExtern);
+ break;
+ }
+ } else if (CGM.getCodeGenOpts().FunctionReturnThunks)
+ Fn->addFnAttr(llvm::Attribute::FnRetThunkExtern);
+ }
+
if (FD && (getLangOpts().OpenCL ||
(getLangOpts().HIP && getLangOpts().CUDAIsDevice))) {
// Add metadata for a kernel function.
Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -1998,6 +1998,13 @@
HelpText<"Enable cf-protection in 'full' mode">;
def mibt_seal : Flag<["-"], "mibt-seal">, Group<m_Group>, Flags<[CoreOption, CC1Option]>,
HelpText<"Optimize fcf-protection=branch/full (requires LTO).">;
+def mfunction_return_EQ : Joined<["-"], "mfunction-return=">,
+ Group<m_Group>, Flags<[CoreOption, CC1Option]>,
+ HelpText<"Replace returns with jumps to ``__x86_return_thunk`` (x86 only, error otherwise)">,
+ Values<"keep,thunk-extern">,
+ NormalizedValues<["Keep", "Extern"]>,
+ NormalizedValuesScope<"llvm::FunctionReturnThunksKind">,
+ MarshallingInfoEnum<CodeGenOpts<"FunctionReturnThunks">, "Keep">;
defm xray_instrument : BoolFOption<"xray-instrument",
LangOpts<"XRayInstrument">, DefaultFalse,
Index: clang/include/clang/Basic/CodeGenOptions.def
===================================================================
--- clang/include/clang/Basic/CodeGenOptions.def
+++ clang/include/clang/Basic/CodeGenOptions.def
@@ -107,6 +107,7 @@
CODEGENOPT(CFProtectionBranch , 1, 0) ///< if -fcf-protection is
///< set to full or branch.
CODEGENOPT(IBTSeal, 1, 0) ///< set to optimize CFProtectionBranch.
+CODEGENOPT(FunctionReturnThunks, 1, 0) ///< -mfunction-return={keep|thunk-extern}
CODEGENOPT(XRayInstrumentFunctions , 1, 0) ///< Set when -fxray-instrument is
///< enabled.
Index: clang/include/clang/Basic/AttrDocs.td
===================================================================
--- clang/include/clang/Basic/AttrDocs.td
+++ clang/include/clang/Basic/AttrDocs.td
@@ -6606,6 +6606,27 @@
}
return 0;
}
+ }];
+}
+
+def FunctionReturnThunksDocs : Documentation {
+ let Category = DocCatFunction;
+ let Content = [{
+The attribute ``function_return`` can replace return instructions with jumps to
+target-specific symbols. This attribute supports 2 possible values,
+corresponding to the values supported by the ``-mfunction-return=`` command
+line flag:
+* ``__attribute__((function_return("keep")))`` to disable related transforms.
+ This is useful for undoing global setting from ``-mfunction-return=`` locally
+ for individual functions.
+* ``__attribute__((function_return("thunk-extern")))`` to replace returns with
+ jumps, while NOT emitting the thunk.
+
+The values ``thunk`` and ``thunk-inline`` from GCC are not supported.
+
+The symbol used for ``thunk-extern`` is target specific:
+* X86: ``__x86_return_thunk``
+As such, this function attribute is currently only supported on X86 targets.
}];
}
Index: clang/include/clang/Basic/Attr.td
===================================================================
--- clang/include/clang/Basic/Attr.td
+++ clang/include/clang/Basic/Attr.td
@@ -4036,3 +4036,14 @@
let LangOpts = [COnly];
}
def : MutualExclusions<[RandomizeLayout, NoRandomizeLayout]>;
+
+def FunctionReturnThunks : InheritableAttr,
+ TargetSpecificAttr<TargetAnyX86> {
+ let Spellings = [GCC<"function_return">];
+ let Args = [EnumArgument<"ThunkType", "Kind",
+ ["keep", "thunk-extern"],
+ ["Keep", "Extern"]
+ >];
+ let Subjects = SubjectList<[Function]>;
+ let Documentation = [FunctionReturnThunksDocs];
+}
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -404,6 +404,12 @@
format string must correctly format the fixed parameter types of the function.
Using the attribute this way emits a GCC compatibility diagnostic.
+- Support was added for ``__attribute__((function_return("thunk-extern")))``
+ to X86 to replace ``ret`` instructions with ``jmp __x86_return_thunk``. The
+ corresponding attribute to disable this,
+ ``__attribute__((function_return("keep")))`` was added. This is intended to
+ be used by the Linux kernel to mitigate RETBLEED.
+
Windows Support
---------------
@@ -556,6 +562,9 @@
this instruction (see rdpruintrin.h).
- Support ``-mstack-protector-guard-symbol=[SymbolName]`` to use the given
symbol for addressing the stack protector guard.
+- ``-mfunction-return=thunk-extern`` support was added to clang for x86. This
+ will be used by Linux kernel mitigations for RETBLEED. The corresponding flag
+ ``-mfunction-return=keep`` may be appended to disable the feature.
DWARF Support in Clang
----------------------
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