llvm dev - Mar 2016 - GSoC, question on open projects

Hello,

My name is Janek van Oirschot, currently student premaster embedded
systems at the Technical University of Eindhoven and interested in
participating in GSoC and contributing to LLVM. I have some experience
with development for the GNU Assembler in which I looked into
assembly-time relaxation.

I have looked at the open projects page, found some interesting
projects but still have some questions about them:

"Add support for 16-bit x86 assembly and real mode to the assembler
and disassembler, for use by BIOS code. This includes both 16-bit
instruction encodings as well as privileged instructions (lgdt, lldt,
ltr, lmsw, clts, invd, invlpg, wbinvd, hlt, rdmsr, wrmsr, rdpmc,
rdtsc) and the control and debug registers."

Correct me if I'm mistaken, but isn't this already implemented in llvm
mc? I haven't searched for every instruction part of these
architectures but I was able find to some of the privileged
instructions for x86's .td definitions; however, maybe I'm
misunderstanding the relation between llvm-mc and llvm-as and which
what this project refers to.

"Write LLVM IR level debugger (extend Interpreter?)"

I haven't found anything that implies this has been worked on. Is this
available? If so, what exactly is meant with this? Using a target's
LLVM bitcode to step through code? Using LLVM's IR to step though a
target's bitcode in the interpreter? Though, these questions might
sound silly as I'm not wel versed yet in the internals.

Kind regards,
Janek van Oirschot

Hi Janek,

I had a quick look at the 16-bit stuff and found that most of it was 
implemented by Intel some time ago.  See also 
http://lists.llvm.org/pipermail/llvm-dev/2014-January/069344.html

There still seem to be some few open issues with compiling the parts of 
the linux kernel boot code using LLVM, which can be found in the 
bugtracker, but you might want to check if they are indeed still open.

Regarding the LLVM IR level debugger, I have no clue and will let 
someone else respond to that.

@list: On a slightly related matter.  Who's responsible for removing 
projects from this list when they are completed?

Cheers,
  Roel



On 15/03/16 14:45, Janek van Oirschot via llvm-dev
wrote:
> Hello,
>
> My name is Janek van Oirschot, currently student premaster embedded
> systems at the Technical University of Eindhoven and interested in
> participating in GSoC and contributing to LLVM. I have some experience
> with development for the GNU Assembler in which I looked into
> assembly-time relaxation.
>
> I have looked at the open projects page, found some interesting
> projects but still have some questions about them:
>
> "Add support for 16-bit x86 assembly and real mode to the assembler
> and disassembler, for use by BIOS code. This includes both 16-bit
> instruction encodings as well as privileged instructions (lgdt, lldt,
> ltr, lmsw, clts, invd, invlpg, wbinvd, hlt, rdmsr, wrmsr, rdpmc,
> rdtsc) and the control and debug registers."
>
> Correct me if I'm mistaken, but isn't this already implemented in
llvm
> mc? I haven't searched for every instruction part of these
> architectures but I was able find to some of the privileged
> instructions for x86's .td definitions; however, maybe I'm
> misunderstanding the relation between llvm-mc and llvm-as and which
> what this project refers to.
>
> "Write LLVM IR level debugger (extend Interpreter?)"
>
> I haven't found anything that implies this has been worked on. Is this
> available? If so, what exactly is meant with this? Using a target's
> LLVM bitcode to step through code? Using LLVM's IR to step though a
> target's bitcode in the interpreter? Though, these questions might
> sound silly as I'm not wel versed yet in the internals.
>
> Kind regards,
> Janek van Oirschot
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>

Hello Roel,

Thanks for your response!

On Sun, Mar 20, 2016 at 8:57 PM, Roel Jordans via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Hi Janek,
>
> I had a quick look at the 16-bit stuff and found that most of it was
> implemented by Intel some time ago.  See also
> http://lists.llvm.org/pipermail/llvm-dev/2014-January/069344.html
>
> There still seem to be some few open issues with compiling the parts of the
> linux kernel boot code using LLVM, which can be found in the bugtracker,
but
> you might want to check if they are indeed still open.
I did a quick search on this in the bugtracker and found
https://llvm.org/bugs/show_bug.cgi?id=4068 which seems to be assigned
already.
> Regarding the LLVM IR level debugger, I have no clue and will let someone
> else respond to that.
I hope somebody can respond on this. I think I understand what is
asked but it's still my interpretation of a one-liner in the open
projects page. I'd love it if I could get a bit more detail on what
the idea was of this project as it was added to the open projects
list.
> @list: On a slightly related matter.  Who's responsible for removing
> projects from this list when they are completed?
>
> Cheers,
>  Roel
Kind regards,
Janek van Oirschot