[LLVMdev] A bug or a feature?

[Anton Yartsev]

On 11.03.2014 3:34, David Blaikie wrote:
> On Mon, Mar 10, 2014 at 4:24 PM, Anton Yartsev <anton.yartsev at gmail.com> wrote:
>> Hi,
>>
>> I've run Clang Static Analyzer checker alpha.cplusplus.NewDeleteLeaks over
>> LLVM codebase to detect false-positives and at the same time eliminate
>> memory leaks. The majority of leaks were detected in lib/Target/* and
>> lib/MC/*. In all cases the similar trick was detected as a leak (example
>> from lib/Target/Sparc/MCTargetDesc/SparcMCTargetDesc.cpp) :
>>
>> static MCStreamer *createMCStreamer(const Target &T, StringRef TT,
>>                                      MCContext &Context, MCAsmBackend &MAB,
>>                                      raw_ostream &OS, MCCodeEmitter *Emitter,
>>                                      const MCSubtargetInfo &STI, bool
>> RelaxAll,
>>                                      bool NoExecStack) {
>>     MCStreamer *S =
>>     createELFStreamer(Context, MAB, OS, Emitter, RelaxAll, NoExecStack);
>>     new SparcTargetELFStreamer(*S);
>>
>>             1    Memory is allocated    →
>>
>>     return S;
>>
>>             2   ←   Potential memory leak
>> }
>>
>> Have not got why is this SparcTargetELFStreamer created dynamically and not
>> assigned.
>> Can anybody please explain is this a trick or a trouble?
> It's a trick - if you look at the MCTargetStreamer ctor (which
> SparcTargetELFStreamer derives from you'll see this:
>
> MCTargetStreamer::MCTargetStreamer(MCStreamer &S) : Streamer(S) {
>    S.setTargetStreamer(this);
> }
>
> So it didn't actually leak... the MCStreamer ('S' in the function you
> showed above) took ownership of the object.
Ah, got it, thank you! Missed passing 'this'.

>
>> The similar pattern was detected in
>> lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp
>> lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.cpp
>> lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.cpp
>> lib/Target/Mips/MCTargetDesc/MipsMCTargetDesc.cpp
>> lib/Target/XCore/MCTargetDesc/XCoreMCTargetDesc.cpp
>> lib/Target/Mips/MCTargetDesc/MipsMCTargetDesc.cpp
>> lib/Target/Sparc/MCTargetDesc/SparcMCTargetDesc.cpp
>> lib/MC/MCELFStreamer.cpp
>> lib/MC/WinCOFFStreamer.cpp
>> lib/MC/MCMachOStreamer.cpp
>>
>> --
>> Anton
>>
>>
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>>


-- 
Anton