[llvm] r244405 - Fix dangling reference in DwarfLinker.cpp. The original code

[Yaron Keren via llvm-commits]

r244455, thanks!

2015-08-10 18:09 GMT+03:00 David Blaikie <dblaikie at gmail.com>:

>
>
> On Sat, Aug 8, 2015 at 2:03 PM, Yaron Keren via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> Author: yrnkrn
>> Date: Sat Aug  8 16:03:19 2015
>> New Revision: 244405
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=244405&view=rev
>> Log:
>> Fix dangling reference in DwarfLinker.cpp. The original code
>>
>>   Seq.emplace_back(Seq.back());
>>
>> does not work as planned, since Seq.back() may become a dangling reference
>> when emplace_back is called and possibly reallocates vector. To avoid
>> this,
>> the vector allocation should be reserved first and only then used.
>>
>> This broke test/tools/dsymutil/X86/custom-line-table.test with Visual C++
>> 2013.
>>
>>
>> Modified:
>>     llvm/trunk/tools/dsymutil/DwarfLinker.cpp
>>
>> Modified: llvm/trunk/tools/dsymutil/DwarfLinker.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/dsymutil/DwarfLinker.cpp?rev=244405&r1=244404&r2=244405&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/tools/dsymutil/DwarfLinker.cpp (original)
>> +++ llvm/trunk/tools/dsymutil/DwarfLinker.cpp Sat Aug  8 16:03:19 2015
>> @@ -2884,6 +2884,7 @@ void DwarfLinker::patchLineTableForUnit(
>>        if (StopAddress != -1ULL && !Seq.empty()) {
>>          // Insert end sequence row with the computed end address, but
>>          // the same line as the previous one.
>> +        Seq.reserve(Seq.size() + 1);
>>          Seq.emplace_back(Seq.back());
>>
>
> Might be less subtle to just write this as:
>
> auto NextLine = Seq.back();
> NextLine.Address = ...;
> ...
> NextLine.EpilogueBegin = ...;
> Seq.push_back(NextLine);
>
> (alternatively: Seq.push_back(DWARFDebugLine::Row(Seq.back()); would also
> avoid the need for the reserve, but would still be bit non-obvious/subtle,
> like the reserve call is)
>
>
>>          Seq.back().Address = StopAddress;
>>          Seq.back().EndSequence = 1;
>>
>>
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>>
>
>
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