[llvm-commits] ARM ELF disassembly with integrated-as

[Tim Northover]

Hi Greg,

Thanks for working on this.

> I could use some help creating a test case for adding mixed-mode support.
> Adding EmitAssemblerFlag() as Tim suggested was no problem, but creating a
> test case that gets llc or llvm-mc to generate a file with both Thumb and
> ARM data sections is.

I think the llc approach is doomed to failure for now. CodeGen just
doesn't produce mixed ARM and Thumb code. That's OK though.

As for llvm-mc, I agree it doesn't seem to emit the required
DataRegion directives. However, temporarily hacking that into the easy
places (EmitDataRegion just before EmitValue and EmitInstruction in
ARMAsmParser) reveals a possibly bigger problem with the approach
taken.

Basically, you can't know that the first symbol emitted in a section
will be a code one until you've got an instruction or .word (etc) in
front of you, so ChangeSection is too early to actually emit it. For
example an assembly file like:
    .text
    .word 42
    add r0, r0, r0
should produce a mapping symbol $d at offset 0, and $a/$t at offset 4.
I think this is impossible with the patch as it stands.

As well as ARMAsmParser.cpp, I think parts of
lib/MC/MCParser/AsmParser.cpp will need to know about the regions
since they handle directives like .byte, .ascii, ...

Cheers.

Tim.