llvm dev - Jun 2014 - [LLVMdev] Any way get debug output of generated assembly from MCJIT without completely redoing CodeGen?

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

By "debug output" you mean actual debug info or something else?

If it's the actual debug info then the answer is no.

-eric

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
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

No, I just mean human-readable text assembly (aka .s file contents equivalent to
what is JIT compiled into memory).  I don't actually have any need for
'actual' debug info, since it doesn't exist in the original IR. 
Sorry my use of 'debug' was confusing.

On Jun 24, 2014, at 3:57 PM, Eric Christopher <echristo at gmail.com>
wrote:
> By "debug output" you mean actual debug info or something else?
> 
> If it's the actual debug info then the answer is no.
> 
> -eric
> 
> 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
>> 
>> 
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

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
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
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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
>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>