Ignore blacklist when generating __cfi_check_fail.

[eugenis]

Summary

Fixes PR37898.

[eugenis]

Another option is to add a special case to blacklist logic to make it not apply to __cfi_check_fail.

Yet another option is to make blacklist not apply to functions without a source location, but that seems to be done intentionally here:
http://llvm-cs.pcc.me.uk/tools/clang/lib/CodeGen/CodeGenModule.cpp#1827

[pcc]

__cfi_check_fail certainly seems like a special case in that its behaviour is controlled only by flags and not the blacklist.

Maybe a simpler fix would be to add this to the top of EmitCfiCheckFail?

SanOpts = CGM.getLangOpts().Sanitize;

[eugenis]

Simplify code.

[eugenis]

Yes, that's better.

[pcc]

LGTM

clang/lib/CodeGen/CGExpr.cpp

void CodeGenFunction::EmitCfiCheckFail() {
   llvm::Function *F = llvm::Function::Create(
       llvm::FunctionType::get(VoidTy, {VoidPtrTy, VoidPtrTy}, false),
       llvm::GlobalValue::WeakODRLinkage, "__cfi_check_fail", &CGM.getModule());
   F->setVisibility(llvm::GlobalValue::HiddenVisibility);
 
   StartFunction(GlobalDecl(), CGM.getContext().VoidTy, F, FI, Args,
                 SourceLocation());
 
+  // This function should not be affected by blacklist. This function does
+  // not have a source location, but "src:*" would still apply. Revert any
+  // changes to SanOpts made in StartFunction.
+  SanOpts = CGM.getLangOpts().Sanitize;
+
   llvm::Value *Data =
       EmitLoadOfScalar(GetAddrOfLocalVar(&ArgData), /*Volatile=*/false,
                        CGM.getContext().VoidPtrTy, ArgData.getLocation());
   llvm::Value *Addr =
       EmitLoadOfScalar(GetAddrOfLocalVar(&ArgAddr), /*Volatile=*/false,
                        CGM.getContext().VoidPtrTy, ArgAddr.getLocation());
 
   // Data == nullptr means the calling module has trap behaviour for this check.

clang/test/CodeGen/cfi-check-fail2.c

 // __cfi_check_fail codegen when not all CFI checkers are enabled.
 // RUN: %clang_cc1 -triple x86_64-unknown-linux -O0 -fsanitize-cfi-cross-dso \
 // RUN:     -fsanitize=cfi-vcall \
 // RUN:     -emit-llvm -o - %s | FileCheck %s
 
+// Check that blacklist does not affect generated code.
+// RUN: echo "src:*" > %t-all.blacklist
+// RUN: %clang_cc1 -triple x86_64-unknown-linux -O0 -fsanitize-cfi-cross-dso \
+// RUN:     -fsanitize=cfi-vcall -fsanitize-blacklist=%t-all.blacklist \
+// RUN:     -emit-llvm -o - %s | FileCheck %s
+
 void caller(void (*f)()) {
   f();
 }
 
 // CHECK: define weak_odr hidden void @__cfi_check_fail(i8*, i8*)
 // CHECK: store i8* %0, i8** %[[ALLOCA0:.*]], align 8
 // CHECK: store i8* %1, i8** %[[ALLOCA1:.*]], align 8
 // CHECK: %[[DATA:.*]] = load i8*, i8** %[[ALLOCA0]], align 8