llvm dev - Oct 2015 - ELF object writing from assembly file

Thanks a lot Tim.

I am getting an error which says: "LLVM ERROR: unable to write nop sequence
of 0 bytes"
Is there any way that I can print out the Obj code (I mean bitstream
representation of the assembly code which is going to be placed in the ELF
file), before making any ELF file?

Cheers,
ES

On Tue, Oct 13, 2015 at 3:02 PM, Tim Northover <t.p.northover at
gmail.com>
wrote:
> On 13 October 2015 at 02:19, Sky Flyer via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > I tried this commands, but it didn't work corrctly:
> >
> > llvm-mc -filetype=obj -arch=test file.s -o=a.o
>
> That looks right to me ("-triple test-elf" might be more robust
and
> work if you're coding on OS X or Windows).
>
> > and I think after an obj file is built, I should use this command but
I
> am
> > not sure!
> >
> > llvm-objdump -arch=test a.o
>
> Either llvm-objdump or llvm-readobj will work. llvm-readobj tends to
> produce lower level information, while llvm-objdump is more
> user-friendly. They ought to mostly work on the generic information
> without changes.
>
> If you want "-d" (disassemble) to work, you're going to have
to
> implement a Disassembler in your target too.
>
> Tim.
>
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On 15 October 2015 at 04:38, Sky Flyer <skylake007 at googlemail.com>
wrote:
> I am getting an error which says: "LLVM ERROR: unable to write nop
sequence
> of 0 bytes"
Sounds like you need to implement "writeNopData" from the AsmBackend.
> Is there any way that I can print out the Obj code (I mean bitstream
> representation of the assembly code which is going to be placed in the ELF
> file), before making any ELF file?
I think it's only really produced on demand while writing the ELF
file. You might look at the output of "llc -debug", which shows some
of the intermediate data structures, none of them are really just the
instruction bits.

Cheers.

Tim.

Hello Tim,

In the writeNopData, I changed the return value to true, and now everything
is fine!
Thanks a lot for your help.

Cheers,
ES

On Thu, Oct 15, 2015 at 6:14 PM, Tim Northover <t.p.northover at
gmail.com>
wrote:
> On 15 October 2015 at 04:38, Sky Flyer <skylake007 at googlemail.com>
wrote:
> > I am getting an error which says: "LLVM ERROR: unable to write
nop
> sequence
> > of 0 bytes"
>
> Sounds like you need to implement "writeNopData" from the
AsmBackend.
>
> > Is there any way that I can print out the Obj code (I mean bitstream
> > representation of the assembly code which is going to be placed in the
> ELF
> > file), before making any ELF file?
>
> I think it's only really produced on demand while writing the ELF
> file. You might look at the output of "llc -debug", which shows
some
> of the intermediate data structures, none of them are really just the
> instruction bits.
>
> Cheers.
>
> Tim.
>
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