-fsanitize=function: use type hashes instead of RTTI objects

Currently we use RTTI objects to check type compatibility. To support non-unique
RTTI objects, commit 5745eccef54ddd3caca278d1d292a88b2281528b added a
`checkTypeInfoEquality` string matching to the runtime.
The scheme is inefficient.

```
_Z1fv:
  .long   846595819                    # jmp
  .long   .L__llvm_rtti_proxy-_Z3funv
  ...

main:
  ...
  # Load the second word (pointer to the RTTI object) and dereference it.
  movslq  4(%rsi), %rax
  movq    (%rax,%rsi), %rdx
  # Is it the desired typeinfo object?
  leaq    _ZTIFvvE(%rip), %rax
  # If not, call __ubsan_handle_function_type_mismatch_v1, which may recover if checkTypeInfoEquality allows
  cmpq    %rax, %rdx
  jne     .LBB1_2
  ...

.section        .data.rel.ro,"aw",@progbits
  .p2align        3, 0x0
.L__llvm_rtti_proxy:
  .quad   _ZTIFvvE
```

Let's replace the indirect `_ZTI` pointer with a type hash similar to
`-fsanitize=kcfi`.

```
_Z1fv:
  .long   3238382334
  .long   2772461324  # type hash

main:
  ...
  # Load the second word (callee type hash) and check whether it is expected
  cmpl    $-1522505972, -4(%rax)
  # If not, fail: call __ubsan_handle_function_type_mismatch
  jne     .LBB2_2
```

The RTTI object derives its name from `clang::MangleContext::mangleCXXRTTI`,
which uses `mangleType`. `mangleTypeName` uses `mangleType` as well. So the
type compatibility change is high-fidelity.

Since we no longer need RTTI pointers in
`__ubsan::__ubsan_handle_function_type_mismatch_v1`, let's switch it back to
version 0, the original signature before
e215996a2932ed7c472f4e94dc4345b30fd0c373 (2019).
`__ubsan::__ubsan_handle_function_type_mismatch_abort` is not
recoverable, so we can revert some changes from
e215996a2932ed7c472f4e94dc4345b30fd0c373.

Reviewed By: samitolvanen

Differential Revision: https://reviews.llvm.org/D148785

1 files changed, 4 insertions, 5 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index dfd8b9e..e9ad5e7 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -117,7 +117,7 @@ enum TypeEvaluationKind {
   SANITIZER_CHECK(DivremOverflow, divrem_overflow, 0)                          \
   SANITIZER_CHECK(DynamicTypeCacheMiss, dynamic_type_cache_miss, 0)            \
   SANITIZER_CHECK(FloatCastOverflow, float_cast_overflow, 0)                   \
-  SANITIZER_CHECK(FunctionTypeMismatch, function_type_mismatch, 1)             \
+  SANITIZER_CHECK(FunctionTypeMismatch, function_type_mismatch, 0)             \
   SANITIZER_CHECK(ImplicitConversion, implicit_conversion, 0)                  \
   SANITIZER_CHECK(InvalidBuiltin, invalid_builtin, 0)                          \
   SANITIZER_CHECK(InvalidObjCCast, invalid_objc_cast, 0)                       \
@@ -2368,10 +2368,9 @@ public:
   /// XRay typed event handling calls.
   bool AlwaysEmitXRayTypedEvents() const;
 
-  /// Decode an address used in a function prologue, encoded by \c
-  /// EncodeAddrForUseInPrologue.
-  llvm::Value *DecodeAddrUsedInPrologue(llvm::Value *F,
-                                        llvm::Value *EncodedAddr);
+  /// Return a type hash constant for a function instrumented by
+  /// -fsanitize=function.
+  llvm::ConstantInt *getUBSanFunctionTypeHash(QualType T) const;
 
   /// EmitFunctionProlog - Emit the target specific LLVM code to load the
   /// arguments for the given function. This is also responsible for naming the