[X86] Support -mindirect-branch-cs-prefix for call and jmp to indirect thunk

This is to address feature request from ClangBuiltLinux/linux#1665

Reviewed By: nickdesaulniers, MaskRay

Differential Revision: https://reviews.llvm.org/D130754

Author: phoebewang

clang/docs/ReleaseNotes.rst

@@ -138,6 +138,8 @@ CUDA Support in Clang
 X86 Support in Clang
 --------------------
 
+- Support ``-mindirect-branch-cs-prefix`` for call and jmp to indirect thunk.
+
 DWARF Support in Clang
 ----------------------
 

clang/include/clang/Basic/CodeGenOptions.def

@@ -108,6 +108,8 @@ 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(IndirectBranchCSPrefix, 1, 0) ///< if -mindirect-branch-cs-prefix
+                                         ///< is set.
 
 CODEGENOPT(XRayInstrumentFunctions , 1, 0) ///< Set when -fxray-instrument is
                                            ///< enabled.

clang/include/clang/Driver/Options.td

@@ -2025,6 +2025,10 @@ def mfunction_return_EQ : Joined<["-"], "mfunction-return=">,
   NormalizedValues<["Keep", "Extern"]>,
   NormalizedValuesScope<"llvm::FunctionReturnThunksKind">,
   MarshallingInfoEnum<CodeGenOpts<"FunctionReturnThunks">, "Keep">;
+def mindirect_branch_cs_prefix : Flag<["-"], "mindirect-branch-cs-prefix">,
+  Group<m_Group>, Flags<[CoreOption, CC1Option]>,
+  HelpText<"Add cs prefix to call and jmp to indirect thunk">,
+  MarshallingInfoFlag<CodeGenOpts<"IndirectBranchCSPrefix">>;
 
 defm xray_instrument : BoolFOption<"xray-instrument",
   LangOpts<"XRayInstrument">, DefaultFalse,

clang/lib/CodeGen/CodeGenModule.cpp

@@ -775,6 +775,9 @@ void CodeGenModule::Release() {
   if (CodeGenOpts.FunctionReturnThunks)
     getModule().addModuleFlag(llvm::Module::Override, "function_return_thunk_extern", 1);
 
+  if (CodeGenOpts.IndirectBranchCSPrefix)
+    getModule().addModuleFlag(llvm::Module::Override, "indirect_branch_cs_prefix", 1);
+
   // Add module metadata for return address signing (ignoring
   // non-leaf/all) and stack tagging. These are actually turned on by function
   // attributes, but we use module metadata to emit build attributes. This is

clang/lib/Driver/ToolChains/Clang.cpp

@@ -6359,6 +6359,8 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     CmdArgs.push_back(
         Args.MakeArgString(Twine("-mfunction-return=") + A->getValue()));
 
+  Args.AddLastArg(CmdArgs, options::OPT_mindirect_branch_cs_prefix);
+
   // 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.

clang/test/CodeGen/X86/indirect-branch-cs-prefix.c

@@ -0,0 +1,4 @@
+// RUN: %clang -target i386-unknown-unknown -o - -emit-llvm -S -mindirect-branch-cs-prefix %s | FileCheck %s
+
+// CHECK: !{i32 4, !"indirect_branch_cs_prefix", i32 1}
+void foo() {}

clang/test/Driver/x86_features.c

@@ -6,8 +6,11 @@
 // RUN: %clang -### %s -mieee-fp -S 2>&1 | FileCheck --check-prefix=IEEE %s
 // IEEE-NOT: error: unknown argument
 
-// RUN: %clang -target i386-unknown-unknown -### %s -mskip-rax-setup -S 2>&1 | FileCheck --check-prefix=SRS %s
+// RUN: %clang --target=i386 -### %s -mskip-rax-setup -S 2>&1 | FileCheck --check-prefix=SRS %s
 // SRS: "-mskip-rax-setup"
 
-// RUN: %clang -target i386-unknown-unknown -### %s -mno-skip-rax-setup -S 2>&1 | FileCheck --check-prefix=NO-SRS %s
+// RUN: %clang --target=i386 -### %s -mno-skip-rax-setup -S 2>&1 | FileCheck --check-prefix=NO-SRS %s
 // NO-SRS-NOT: "-mskip-rax-setup"
+
+// RUN: %clang --target=i386 -### %s -mindirect-branch-cs-prefix -S 2>&1 | FileCheck --check-prefix=IND-CS %s
+// IND-CS: "-mindirect-branch-cs-prefix"

llvm/lib/Target/X86/X86MCInstLower.cpp

@@ -2440,6 +2440,9 @@ void X86AsmPrinter::emitInstruction(const MachineInstr *MI) {
   if (OutStreamer->isVerboseAsm())
     addConstantComments(MI, *OutStreamer);
 
+  bool IndCS =
+      MF->getMMI().getModule()->getModuleFlag("indirect_branch_cs_prefix");
+
   switch (MI->getOpcode()) {
   case TargetOpcode::DBG_VALUE:
     llvm_unreachable("Should be handled target independently");
@@ -2488,13 +2491,16 @@ void X86AsmPrinter::emitInstruction(const MachineInstr *MI) {
     break;
   }
 
+  case X86::TAILJMPd64:
+    if (IndCS && MI->hasRegisterImplicitUseOperand(X86::R11))
+      EmitAndCountInstruction(MCInstBuilder(X86::CS_PREFIX));
+    LLVM_FALLTHROUGH;
   case X86::TAILJMPr:
   case X86::TAILJMPm:
   case X86::TAILJMPd:
   case X86::TAILJMPd_CC:
   case X86::TAILJMPr64:
   case X86::TAILJMPm64:
-  case X86::TAILJMPd64:
   case X86::TAILJMPd64_CC:
   case X86::TAILJMPr64_REX:
   case X86::TAILJMPm64_REX:
@@ -2668,6 +2674,10 @@ void X86AsmPrinter::emitInstruction(const MachineInstr *MI) {
                                 .addImm(MI->getOperand(0).getImm())
                                 .addReg(X86::NoRegister));
     return;
+  case X86::CALL64pcrel32:
+    if (IndCS && MI->hasRegisterImplicitUseOperand(X86::R11))
+      EmitAndCountInstruction(MCInstBuilder(X86::CS_PREFIX));
+    break;
   }
 
   MCInst TmpInst;

llvm/lib/Target/X86/X86ReturnThunks.cpp

@@ -34,6 +34,7 @@
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/MachineInstr.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
 #include "llvm/MC/MCInstrDesc.h"
 #include "llvm/Support/Debug.h"
 
@@ -73,9 +74,14 @@ bool X86ReturnThunks::runOnMachineFunction(MachineFunction &MF) {
       if (Term.getOpcode() == RetOpc)
         Rets.push_back(&Term);
 
+  bool IndCS =
+      MF.getMMI().getModule()->getModuleFlag("indirect_branch_cs_prefix");
+  const MCInstrDesc &CS = ST.getInstrInfo()->get(X86::CS_PREFIX);
   const MCInstrDesc &JMP = ST.getInstrInfo()->get(X86::TAILJMPd);
 
   for (MachineInstr *Ret : Rets) {
+    if (IndCS)
+      BuildMI(Ret->getParent(), Ret->getDebugLoc(), CS);
     BuildMI(Ret->getParent(), Ret->getDebugLoc(), JMP)
         .addExternalSymbol(ThunkName.data());
     Ret->eraseFromParent();

llvm/test/CodeGen/X86/attr-function-return.ll

@@ -6,6 +6,11 @@
 define void @x() fn_ret_thunk_extern {
 ; CHECK-LABEL: x:
 ; CHECK:       # %bb.0:
+; CHECK-NEXT:    cs
 ; CHECK-NEXT:    jmp __x86_return_thunk
   ret void
 }
+
+!llvm.module.flags = !{!0}
+
+!0 = !{i32 4, !"indirect_branch_cs_prefix", i32 1}