[cfe-dev] [PATCH] Integer Sanitizer Initial Patches

[Eli Friedman]

Sorry about the late reply.  Yes, I think my concerns have been
addressed; thanks.

-Eli

On Mon, Nov 19, 2012 at 12:38 PM, Richard Smith <richard at metafoo.co.uk> wrote:
> Eli: have your concerns been suitably addressed here?
>
> On Fri, Nov 9, 2012 at 4:09 PM, Will Dietz <willdtz at gmail.com> wrote:
>> Thank you for your comments.
>>
>> Updated patches attached!
>>
>> ~Will
>>
>> On Thu, Nov 8, 2012 at 5:08 PM, Richard Smith <richard at metafoo.co.uk> wrote:
>>> Hi,
>>>
>>> On Wed, Nov 7, 2012 at 5:15 PM, Will Dietz <willdtz at gmail.com> wrote:
>>>> 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 (http://llvm.org/bugs/show_bug.cgi?id=14247), 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.