[LLVMdev] Directly generating binary file

[Chris Lattner]

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

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