[LLVMdev] Any way get debug output of generated assembly from MCJIT without completely redoing CodeGen?

[Lang Hames]

This actually came up today in a related conversation I had with David Blaikie about RuntimeDyld testing.

As Eric suggested, it would be nice to have a command line flag for something like this. I'd prefer to just dump objects to disk by default though, rather than disassemble them: Once they're dumped they can be disassembled and poked at via existing tools at leisure.

Cheers,
Lang.

Sent from my iPad

> On Jun 24, 2014, at 6:09 PM, sathvik <sathvikl at gmail.com> wrote:
> 
> Hi Craig,
> 
> I am trying to JIT PHP code and this is a hack ..
> https://github.com/sathvikl/llvm/blob/master/lib/ExecutionEngine/OProfileJIT/OProfileJITEventListener.cpp
> 
> It writes out file of JITed methods in /tmp using the OProfileJIT interface so if you register via the OProfile interface 
> + JITEventListener *event_listener = JITEventListener::createOProfileJITEventListener()
> + llvm_engine->RegisterJITEventListener(event_listener) 
> 
> and run oprofile, it will dump out the file with JITed methods into a file. If you use a disassembler, you can try libxed 
> https://github.com/facebook/hhvm/blob/10b2a6a3a8075b676ea167ea49e6bba5b8cca68e/hphp/util/disasm.cpp 
> shows how to use it. 
> libxed is packaged here - 
> https://software.intel.com/en-us/articles/pin-a-binary-instrumentation-tool-downloads
> 
> I plan to write a cleaner interface for this so you can view it via perf but didn't get to it.
> 
> sathvik 
>  
> 
> 
> 
>> On Tue, Jun 24, 2014 at 4:03 PM, Eric Christopher <echristo at gmail.com> wrote:
>> Yeah, that's probably how I'd do it.
>> 
>> Might be useful if you guys want to contribute that as a command line
>> option Kevin.
>> 
>> -eric
>> 
>> On Tue, Jun 24, 2014 at 3:03 PM, Kevin Modzelewski <kmod at dropbox.com> wrote:
>> > We do this in Pyston using a JITEventListener that just disassembles the
>> > output; it's "it works let's move on"-quality:
>> > https://github.com/dropbox/pyston/blob/master/src/codegen/dis.cpp
>> >
>> > I'm not sure how efficient the disassembling is, but at least the process is
>> > pretty self-contained.
>> >
>> >
>> > On Tue, Jun 24, 2014 at 1:33 PM, Craig Smith <craig at ni.com> wrote:
>> >>
>> >>
>> >> Hello all,
>> >>
>> >> I'm trying to hack MCJIT::emitObject to optionally output the
>> >> corresponding text assembly associated with the object code being emitted
>> >> (if a debug flag is set in the app/dev environment which is hosting LLVM).
>> >> I attempted to do this by adding another AsmPrinter pass to the
>> >> PassManager, but this runs into all sorts of problems because there's only
>> >> once MCContext and one MachneModuleInfo pass maintaining various state
>> >> information (MCSections, MCSymbols, etc.) and the two AsmPrinter passes
>> >> interfere with each other.
>> >>
>> >> The only way I've been able to get this to work is to create an entirely
>> >> separate PassManager, and use addPassesToEmitFile() on it, which will redo
>> >> the entire CodeGen process again unnecessarily.
>> >> Does anyone have any ideas/pointers on how I might do this efficiently?
>> >> This is only for a debugging aid, but I'd like to not have to compile
>> >> everything twice when it's enabled.
>> >>
>> >> Thanks
>> >> Craig
>> >>
>> >>
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