GNU Cauldron talk on libgccjit

[David Malcolm]

On Wed, 2014-07-30 at 18:38 +0100, Philip Herron wrote:
> Great presentation I was meant to be there but stuff came up will
> deffo need to make it to the next one!

Thanks!  Cauldron was a lot of fun.

> The assembler as shared library I have it in my github but i haven't
> found how to work with the assembler yet the API seems pretty
> complicated so I didn't really spend enough time on it but my new job
> is more open source friendly so I am hoping to fix that :).

This is
  https://github.com/redbrain/binutils-gdb/tree/libasm
right?

A while back I had a go at trying to isolate state within gas, trying to
pass a "context" object around, but rapidly ran into the realization
that with that approach I was going to need to touch basically every
function in the code.

In the discussion about this at the Cauldron talk, someone pointed out
that it isn't necessary to do it so cleanly for a first iteration: we
can just have a big global mutex inside the assembler library guarding
access to the pre-existing code/data, and then hide that behind a clean
and minimal API for what's needed: access to buffers for the code, data,
bss etc.

So I think the steps here might be:

(A) get support into binutils to support building gas as a library, with
a configure-time option to enable -fPIC so that it can be built as a
shared library (analogous to the --enable-host-shared option I added to
gcc:
https://gcc.gnu.org/ml/gcc-patches/2013-10/msg00637.html )

Then, in parallel:
(B.1) create a testbed client program to *use* the "libasm" API, perhaps
a "run-asm" tool that can run a .s in-process (by assembling it to
code).
(B.2) write the libasm API, wrapping the existing assembler code

[on the grounds that the only way to write a good API is to write
something *using* that API at the same time, to get the rough edges off]

Then:
(C) port libgccjit to use the libasm API

and eventually:
(D) clean up the cruft within libasm, to eventually eliminate the mutex.


Thoughts?

Dave

> > On 30 Jul 2014, at 15:39, David Malcolm <dmalcolm@redhat.com> wrote:
> > 
> > I gave a talk on the JIT library at the GNU Tools Cauldron 2014 meeting
> > in Cambridge UK a week and a half ago:
> > 
> > "Just-In-Time compilation using GCC (libgccjit.so)"
> > 
> > HTML slides can be seen at:
> > http://dmalcolm.fedorapeople.org/presentations/cauldron-2014/jit/
> > 
> > The source code used for generating the HTML slides:
> > https://github.com/davidmalcolm/2014-cauldron-jit-talk/blob/master/source/index.rst
> > 
> > (built using Sphinx, and hieroglyph.io)
> > 
> > I'm not sure if the talk was recorded.
> > 
> > Dave
> >