[libubsan] Handling of floating-point types

[Kostya Serebryany]

... and I had to disable the test for -m32 in r209517
because there are bots that don't work with -m32:
http://lab.llvm.org:8011/builders/llvm-clang-lld-x86_64-centos-6.5/builds/5151/steps/test/logs/stdio


On Fri, May 23, 2014 at 6:55 PM, Kostya Serebryany <kcc at google.com> wrote:

>
>
>
> On Thu, May 22, 2014 at 9:39 PM, Marek Polacek <polacek at redhat.com> wrote:
>
>> Hi!
>>
>> I'm trying to implement -fsanitize=float-cast-overflow support to GCC.
>> One of the issues is that libubsan doesn't handle 96-bit floating-point
>> types, so e.g. on
>>
>> int
>> main ()
>> {
>>   volatile long double ld = 300.0;
>>   char c = ld;
>>   return 0;
>> }
>>
>> with -m32 we hit
>> ==27463==Sanitizer CHECK failed:
>> /builddir/build/BUILD/llvm-3.4/projects/compiler-rt/lib/ubsan/ubsan_value.cc:100
>> ((0 && "unexpected floating point bit width")) != (0) (0, 0)
>>
>> The same for __float80 types in -m32 mode (but since clang doesn't
>> support __float{80,128} types, this is not so relevant for you I guess).
>> Fix is simple:
>>
>> diff --git a/libsanitizer/ubsan/ubsan_value.cc
>> b/libsanitizer/ubsan/ubsan_value.cc
>> index 141e8b5..e2f664d 100644
>> --- a/libsanitizer/ubsan/ubsan_value.cc
>> +++ b/libsanitizer/ubsan/ubsan_value.cc
>> @@ -92,6 +92,7 @@ FloatMax Value::getFloatValue() const {
>>      switch (getType().getFloatBitWidth()) {
>>      case 64: return *reinterpret_cast<double*>(Val);
>>      case 80: return *reinterpret_cast<long double*>(Val);
>> +    case 96: return *reinterpret_cast<long double*>(Val);
>>      case 128: return *reinterpret_cast<long double*>(Val);
>>      }
>>    }
>>
>
>
>> Could someone please review & commit this one?
>>
>
> Thanks! Committed with a tests and and another related fix:
> http://llvm.org/viewvc/llvm-project?view=revision&revision=209516
>
> Alexey, Nick, do we want to have in ubsan the same lit magic as in asan
> that runs all the tests in both 32-bit and 64-bit?
> Currently the ubsan tests seem to be running only in one bit-ness.
>
>
>>
>> Another issue is printing of __float128 and _Decimal{32,64,128} types;
>> libubsan doesn't handle such types, so currently there's no way how
>> to print them.  Unfortunately, I don't think the solution is as simple
>> as adding e.g. TK_Decimal/TK_Float_Extended constants, because
>> libstdc++ I think doesn't have the routines to convert such values to
>> strings, and adding extra library dependencies to e.g. libdecnumber
>> doesn't sound viable.  But for these rather obscure types we can use
>> TK_Unknown - and just print "<unknown>".  I'd guess that DFP types
>> are rare anyway and I'm fine with keeping it this way.
>>
>> Thanks.
>>
>>         Marek
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>>
>
>
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