llvm dev - Feb 2006 - [LLVMdev] Re: Directly generating binary file

Hi!

I'm looking for a way to make the the "llc" tool (or any other
tool),
directly produce a binary file for some target.

The TargetMachine class has a method 'addPassesToEmitMachineCode',
that's
suitable for that, but that method also requires an instance of
MachineCodeEmitter.

The existing MachineCodeEmitter derived classes are either debug-only
(writing to std::cerr), or for JIT, or for ELF (which is not used anywhere,
BTW).

Ideally, I'd like to create my own MachineCodeEmitter derived class, load it
into llc with the -load option, and then have new option for 'llc' that
will use MachineCodeEmitter, not AssemblyWriter, to generate the file.

The reason I'm trying to do this is that the target does not have an
assembler, and does not need it, and so designing an assembler syntax just
for the sake of code generation does not seem right.

Any suggestions how I should proceed?

Thanks,
Volodya

On Mon, 27 Feb 2006, Vladimir Prus wrote:
> I'm looking for a way to make the the "llc" tool (or any
other tool),
> directly produce a binary file for some target.
ok
> The TargetMachine class has a method 'addPassesToEmitMachineCode',
that's
> suitable for that, but that method also requires an instance of
> MachineCodeEmitter.
Actually, you probably want to plug into the addPassesToEmitFile API, when 
FileType is set to ObjectFile.  X86TargetMachine::addPassesToEmitFile 
demonstrates how to do this.
> The existing MachineCodeEmitter derived classes are either debug-only
> (writing to std::cerr), or for JIT, or for ELF (which is not used anywhere,
> BTW).
> Ideally, I'd like to create my own MachineCodeEmitter derived class,
load it
> into llc with the -load option, and then have new option for 'llc'
that
> will use MachineCodeEmitter, not AssemblyWriter, to generate the file.
Yup, the ELFWriter.cpp file should be a reasonable template to base your 
work on, but note that it is not complete at this point.
> The reason I'm trying to do this is that the target does not have an
> assembler, and does not need it, and so designing an assembler syntax just
> for the sake of code generation does not seem right.
Ok.
> Any suggestions how I should proceed?
I'd suggest following the pattern of the ElfWriter.  Basically, the elf 
writer knows about the object file format (ELF in this case, obviously) 
but doesn't know anything specific about the target.  The target handles 
translation of MachineInstr's to relocatable machine code and relocations, 
sending the result to the MachineCodeEmitter.  You can then format it 
according to the requirements of the object file format.

Alternatively, you could side step all of this and write your own .o file 
writer that doesn't use the MachineCodeEmitter interfaces at all.  If this 
is easiest, go for it.

Note that *some* assembler format is useful for debugging, writting 
regression tests, etc.

-Chris

-- 
http://nondot.org/sabre/
http://llvm.org/

Chris Lattner wrote:
>> The TargetMachine class has a method
'addPassesToEmitMachineCode', that's
>> suitable for that, but that method also requires an instance of
>> MachineCodeEmitter.
> 
> Actually, you probably want to plug into the addPassesToEmitFile API, when
> FileType is set to ObjectFile.  X86TargetMachine::addPassesToEmitFile
> demonstrates how to do this.
Ok. Note, however, that online HTML docs for "llc", as well as
"llc.pod" in
the current CVS don't mention the "filetype" option that is used
to control
file format. 

And, should 'addPassesToEmitMachineCode' method be declared deprecated?
>> Any suggestions how I should proceed?
> 
> I'd suggest following the pattern of the ElfWriter.  Basically, the elf
> writer knows about the object file format (ELF in this case, obviously)
> but doesn't know anything specific about the target.  The target
handles
> translation of MachineInstr's to relocatable machine code and
relocations,
> sending the result to the MachineCodeEmitter.  You can then format it
> according to the requirements of the object file format.
> 
> Alternatively, you could side step all of this and write your own .o file
> writer that doesn't use the MachineCodeEmitter interfaces at all.  If
this
> is easiest, go for it.
So far this looks the simplest approach. Especially sincelooking at
ELFCodeEmitter, I see quite a bunch of unimplemented methods.
> Note that *some* assembler format is useful for debugging, writting
> regression tests, etc.
Sure, I plan to have some format that will be output by disassembler, but
don't plan to ever read that format ;-)

- Volodya