Add support for __declspec(guard(nocf))

Summary:
Avoid using the `nocf_check` attribute with Control Flow Guard. Instead, use a
new `"guard_nocf"` function attribute to indicate that checks should not be
added on indirect calls within that function. Add support for
`__declspec(guard(nocf))` following the same syntax as MSVC.

Reviewers: rnk, dmajor, pcc, hans, aaron.ballman

Reviewed By: aaron.ballman

Subscribers: aaron.ballman, tomrittervg, hiraditya, cfe-commits, llvm-commits

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D72167

4 files changed, 26 insertions, 28 deletions

diff --git a/llvm/lib/Transforms/CFGuard/CFGuard.cpp b/llvm/lib/Transforms/CFGuard/CFGuard.cpp
index 3eca00691e0..7c5e90cb53c 100644
--- a/llvm/lib/Transforms/CFGuard/CFGuard.cpp
+++ b/llvm/lib/Transforms/CFGuard/CFGuard.cpp
@@ -254,8 +254,8 @@ bool CFGuard::doInitialization(Module &M) {
 
 bool CFGuard::runOnFunction(Function &F) {
 
-  // Skip modules and functions for which CFGuard checks have been disabled.
-  if (cfguard_module_flag != 2 || F.hasFnAttribute(Attribute::NoCfCheck))
+  // Skip modules for which CFGuard checks have been disabled.
+  if (cfguard_module_flag != 2)
     return false;
 
   SmallVector<CallBase *, 8> IndirectCalls;
@@ -267,17 +267,15 @@ bool CFGuard::runOnFunction(Function &F) {
   for (BasicBlock &BB : F.getBasicBlockList()) {
     for (Instruction &I : BB.getInstList()) {
       auto *CB = dyn_cast<CallBase>(&I);
-      if (CB && CB->isIndirectCall()) {
+      if (CB && CB->isIndirectCall() && !CB->hasFnAttr("guard_nocf")) {
         IndirectCalls.push_back(CB);
         CFGuardCounter++;
       }
     }
   }
 
-  // If no checks are needed, return early and add this attribute to indicate
-  // that subsequent CFGuard passes can skip this function.
+  // If no checks are needed, return early.
   if (IndirectCalls.empty()) {
-    F.addFnAttr(Attribute::NoCfCheck);
     return false;
   }
 
diff --git a/llvm/test/CodeGen/AArch64/cfguard-checks.ll b/llvm/test/CodeGen/AArch64/cfguard-checks.ll
index 627741c4b6f..5ebe1dd1365 100644
--- a/llvm/test/CodeGen/AArch64/cfguard-checks.ll
+++ b/llvm/test/CodeGen/AArch64/cfguard-checks.ll
@@ -7,22 +7,22 @@
 declare i32 @target_func()
 
 
-; Test that Control Flow Guard checks are not added to functions with nocf_checks attribute.
-define i32 @func_nocf_checks() #0 {
+; Test that Control Flow Guard checks are not added on calls with the "guard_nocf" attribute.
+define i32 @func_guard_nocf() {
 entry:
   %func_ptr = alloca i32 ()*, align 8
   store i32 ()* @target_func, i32 ()** %func_ptr, align 8
   %0 = load i32 ()*, i32 ()** %func_ptr, align 8
-  %1 = call i32 %0()
+  %1 = call i32 %0() #0
   ret i32 %1
 
-  ; CHECK-LABEL: func_nocf_checks
+  ; CHECK-LABEL: func_guard_nocf
   ; CHECK:       adrp x8, target_func
 	; CHECK:       add x8, x8, target_func
   ; CHECK-NOT:   __guard_check_icall_fptr
 	; CHECK:       blr x8
 }
-attributes #0 = { nocf_check }
+attributes #0 = { "guard_nocf" }
 
 
 ; Test that Control Flow Guard checks are added even at -O0.
diff --git a/llvm/test/CodeGen/ARM/cfguard-checks.ll b/llvm/test/CodeGen/ARM/cfguard-checks.ll
index c75afc614c7..3fab04eb166 100644
--- a/llvm/test/CodeGen/ARM/cfguard-checks.ll
+++ b/llvm/test/CodeGen/ARM/cfguard-checks.ll
@@ -7,26 +7,27 @@
 declare i32 @target_func()
 
 
-; Test that Control Flow Guard checks are not added to functions with nocf_checks attribute.
-define i32 @func_nocf_checks() #0 {
+; Test that Control Flow Guard checks are not added on calls with the "guard_nocf" attribute.
+define i32 @func_guard_nocf() #0 {
 entry:
   %func_ptr = alloca i32 ()*, align 8
   store i32 ()* @target_func, i32 ()** %func_ptr, align 8
   %0 = load i32 ()*, i32 ()** %func_ptr, align 8
-  %1 = call arm_aapcs_vfpcc i32 %0()
+  %1 = call arm_aapcs_vfpcc i32 %0() #1
   ret i32 %1
 
-  ; CHECK-LABEL: func_nocf_checks
+  ; CHECK-LABEL: func_guard_nocf
   ; CHECK:       movw r0, :lower16:target_func
 	; CHECK:       movt r0, :upper16:target_func
   ; CHECK-NOT:   __guard_check_icall_fptr
 	; CHECK:       blx r0
 }
-attributes #0 = { nocf_check "target-cpu"="cortex-a9" "target-features"="+armv7-a,+dsp,+fp16,+neon,+strict-align,+thumb-mode,+vfp3"}
+attributes #0 = { "target-cpu"="cortex-a9" "target-features"="+armv7-a,+dsp,+fp16,+neon,+strict-align,+thumb-mode,+vfp3"}
+attributes #1 = { "guard_nocf" }
 
 
 ; Test that Control Flow Guard checks are added even at -O0.
-define i32 @func_optnone_cf() #1 {
+define i32 @func_optnone_cf() #2 {
 entry:
   %func_ptr = alloca i32 ()*, align 8
   store i32 ()* @target_func, i32 ()** %func_ptr, align 8
@@ -47,11 +48,11 @@ entry:
 	; CHECK:       blx r1
 	; CHECK-NEXT:  blx r4
 }
-attributes #1 = { noinline optnone "target-cpu"="cortex-a9" "target-features"="+armv7-a,+dsp,+fp16,+neon,+strict-align,+thumb-mode,+vfp3"}
+attributes #2 = { noinline optnone "target-cpu"="cortex-a9" "target-features"="+armv7-a,+dsp,+fp16,+neon,+strict-align,+thumb-mode,+vfp3"}
 
 
 ; Test that Control Flow Guard checks are correctly added in optimized code (common case).
-define i32 @func_cf() #2 {
+define i32 @func_cf() #0 {
 entry:
   %func_ptr = alloca i32 ()*, align 8
   store i32 ()* @target_func, i32 ()** %func_ptr, align 8
@@ -70,11 +71,10 @@ entry:
 	; CHECK:       blx r1
 	; CHECK-NEXT:  blx r4
 }
-attributes #2 = { "target-cpu"="cortex-a9" "target-features"="+armv7-a,+dsp,+fp16,+neon,+strict-align,+thumb-mode,+vfp3"}
 
 
 ; Test that Control Flow Guard checks are correctly added on invoke instructions.
-define i32 @func_cf_invoke() #2 personality i8* bitcast (void ()* @h to i8*) {
+define i32 @func_cf_invoke() #0 personality i8* bitcast (void ()* @h to i8*) {
 entry:
   %0 = alloca i32, align 4
   %func_ptr = alloca i32 ()*, align 8
@@ -112,7 +112,7 @@ declare void @h()
 %struct._SETJMP_FLOAT128 = type { [2 x i64] }
 @buf1 = internal global [16 x %struct._SETJMP_FLOAT128] zeroinitializer, align 16
 
-define i32 @func_cf_setjmp() #2 {
+define i32 @func_cf_setjmp() #0 {
   %1 = alloca i32, align 4
   %2 = alloca i32, align 4
   store i32 0, i32* %1, align 4
diff --git a/llvm/test/CodeGen/X86/cfguard-checks.ll b/llvm/test/CodeGen/X86/cfguard-checks.ll
index 6e8d71411e8..8da06680cf5 100644
--- a/llvm/test/CodeGen/X86/cfguard-checks.ll
+++ b/llvm/test/CodeGen/X86/cfguard-checks.ll
@@ -8,26 +8,26 @@
 declare i32 @target_func()
 
 
-; Test that Control Flow Guard checks are not added to functions with nocf_checks attribute.
-define i32 @func_nocf_checks() #0 {
+; Test that Control Flow Guard checks are not added on calls with the "guard_nocf" attribute.
+define i32 @func_guard_nocf() {
 entry:
   %func_ptr = alloca i32 ()*, align 8
   store i32 ()* @target_func, i32 ()** %func_ptr, align 8
   %0 = load i32 ()*, i32 ()** %func_ptr, align 8
-  %1 = call i32 %0()
+  %1 = call i32 %0() #0
   ret i32 %1
 
-  ; X32-LABEL: func_nocf_checks
+  ; X32-LABEL: func_guard_nocf
   ; X32: 	     movl  $_target_func, %eax
   ; X32-NOT: __guard_check_icall_fptr
 	; X32: 	     calll *%eax
 
-  ; X64-LABEL: func_nocf_checks
+  ; X64-LABEL: func_guard_nocf
   ; X64:       leaq	target_func(%rip), %rax
   ; X64-NOT: __guard_dispatch_icall_fptr
   ; X64:       callq	*%rax
 }
-attributes #0 = { nocf_check }
+attributes #0 = { "guard_nocf" }
 
 
 ; Test that Control Flow Guard checks are added even at -O0.