Hi,
Attached are patches that add a new 'sanitizer' to clang for detecting
and reporting integer overfllows. Unlike the checks added by
-fcatch-undefined-behavior, these also include non-undefined-behavior
checks.
This seems like it could be valuable to me, and I think it's in scope
as a -fsanitize= feature (there are some other checks which I'd like
to eventually include in -fsanitize=, which check for possible bugs
which don't result in undefined behavior). For instance, I could
imagine this being something people would turn on when their code is
behaving strangely, as part of a "tell me about suspicious things that
my program did" mode, but that would depend on making these
diagnostics non-fatal (and maybe supporting a suppression system).
Assuming we reach consensus that we want this...
The attached clang patch adds:
-fsanitize=unsigned-integer-overflow
and
-fsanitize=integer
The first adds support for inserting checks for unsigned integer
overflow, the latter is a new 'sanitizer group' which is used to
enable all integer-related checking. In the future I'd like to
include value-losing conversions, but for now this includes the
existing checks (signed overflow, divide-by-zero, shifts) as well as
the new unsigned overflow checks.
Please split the divide-by-zero check into integer and floating-point
cases, and only include the integer case in the -fsanitize=integer
group.
Please also provide a patch to the user's manual documenting the new arguments.
Also attached is a corresponding patch for compiler-rt that extends
ubsan to include support for reporting unsigned as well as signed
overflows.
Two issues with this that I'm hoping can be discussed:
* As per PR14247 (14247 – -fcatch-undefined-behavior should allow severity levels and recoverability), the
ubsan checks presently aren't recoverable. This reduces these checks'
utility for quickly getting a new large codebase into shape as
mentioned in that bug, but this is of course even more important to be
made optional when reporting unsigned overflows is enabled as well.
I think this is something we should pursue. My only reservation here
is a concern about the performance impact of making the checks
recoverable, but I have no data there.
* Extending "ubsan" is unfortunate given its name, but these checks
don't seem to merit a separate library either. Thoughts?
I don't think that's a problem. "One Hour Photo" is just the name of
the shop, sir. 
Clang patch:
--- a/lib/CodeGen/CGExprScalar.cpp
+++ b/lib/CodeGen/CGExprScalar.cpp
@@ -414,6 +414,11 @@ public:
}
}
+ if (Ops.Ty->isUnsignedIntegerType() &&
+ CGF.getLangOpts().SanitizeUnsignedIntegerOverflow) {
+ return EmitOverflowCheckedBinOp(Ops);
+ }
No braces here, please (and for this same construct later in the file).
case BO_Mul:
case BO_MulAssign:
OpID = 3;
IID = llvm::Intrinsic::smul_with_overflow;
+ IID = isSigned ? llvm::Intrinsic::smul_with_overflow :
+ llvm::Intrinsic::umul_with_overflow;
break;
There's a dead store left behind here.
@@ -2031,7 +2054,8 @@ Value
*ScalarExprEmitter::EmitOverflowCheckedBinOp(const BinOpInfo &Ops) {
if (handlerName->empty()) {
// If the signed-integer-overflow sanitizer is enabled, emit a call to its
// runtime. Otherwise, this is a -ftrapv check, so just emit a trap.
- if (CGF.getLangOpts().SanitizeSignedIntegerOverflow)
+ if (CGF.getLangOpts().SanitizeSignedIntegerOverflow ||
+ CGF.getLangOpts().SanitizeUnsignedIntegerOverflow)
EmitBinOpCheck(Builder.CreateNot(overflow), Ops);
else
CGF.EmitTrapvCheck(Builder.CreateNot(overflow));
This doesn't look right -- building with -ftrapv
-fsanitize=unsigned-integer-overflow will use the -fsanitize path for
signed overflow, not the -ftrapv path.
The Clang patch should include a test -- it's not sufficient for this
to be tested just in the compiler-rt tests (they're not run as a part
of normal Clang development).
compiler-rt patch:
--- a/lib/ubsan/ubsan_handlers.cc
+++ b/lib/ubsan/ubsan_handlers.cc
@@ -55,30 +55,35 @@ void
__ubsan::__ubsan_handle_type_mismatch(TypeMismatchData *Data,
Die();
}
-/// \brief Common diagnostic emission for various forms of signed overflow.
-template<typename T> static void HandleSignedOverflow(OverflowData *Data,
+/// \brief Common diagnostic emission for various forms of integer overflow.
+template<typename T> static void HandleIntegerOverflow(OverflowData *Data,
ValueHandle LHS,
const char *Operator,
- T RHS) {
- Diag(Data->Loc, "signed integer overflow: "
- "%0 %1 %2 cannot be represented in type %3")
+ T RHS,
+ bool isSigned) {
+ Diag(Data->Loc, "%0 integer overflow: "
+ "%1 %2 %3 cannot be represented in type %4")
+ << (isSigned ? "signed" : "unsigned")
Please look at Data->Type.isSignedIntegerTy() in here, rather than
passing in an extra flag.