[compiler-rt] r226913 - [sanitizer] Fix an edge case in MemoryRangeIsAvailable.

[Evgeniy Stepanov]

MemoryRangeIsAvailable treats its argument as [range_start, range_end].
MemoryMappingLayout returns [start, end) intervals.
IntervalsAreSeparate treats both intervals as [start, end].
Looks like the current code is correct, but quite confusing. Shall we
switch to [start, end) intervals everywhere?



On Tue, Jan 27, 2015 at 3:48 PM, Alexey Samsonov <vonosmas at gmail.com> wrote:
> On Fri, Jan 23, 2015 at 7:14 AM, Evgeniy Stepanov
> <eugeni.stepanov at gmail.com> wrote:
>>
>> Author: eugenis
>> Date: Fri Jan 23 09:14:27 2015
>> New Revision: 226913
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=226913&view=rev
>> Log:
>> [sanitizer] Fix an edge case in MemoryRangeIsAvailable.
>>
>> Modified:
>>     compiler-rt/trunk/lib/sanitizer_common/sanitizer_posix.cc
>>
>> Modified: compiler-rt/trunk/lib/sanitizer_common/sanitizer_posix.cc
>> URL:
>> http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/sanitizer_common/sanitizer_posix.cc?rev=226913&r1=226912&r2=226913&view=diff
>>
>> ==============================================================================
>> --- compiler-rt/trunk/lib/sanitizer_common/sanitizer_posix.cc (original)
>> +++ compiler-rt/trunk/lib/sanitizer_common/sanitizer_posix.cc Fri Jan 23
>> 09:14:27 2015
>> @@ -237,7 +237,8 @@ bool MemoryRangeIsAvailable(uptr range_s
>>    while (proc_maps.Next(&start, &end,
>>                          /*offset*/0, /*filename*/0, /*filename_size*/0,
>>                          /*protection*/0)) {
>> -    if (!IntervalsAreSeparate(start, end, range_start, range_end))
>> +    CHECK_NE(0, end);
>> +    if (!IntervalsAreSeparate(start, end - 1, range_start, range_end))
>>        return false;
>>    }
>
>
> I don't believe this is the correct fix. IntervalsAreSeparate should treat
> its arguments as [start1, end1) and [start2, end2), and
> therefore check that (end1 <= start2) || (end2 <= start1);
>
> Otherwise, your change should also subtract one from range_end.
>
>>
>>    return true;
>>
>>
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>
>
>
>
> --
> Alexey Samsonov
> vonosmas at gmail.com