Re: Correct byte compiler error/warning positions. The solution!

[Andrea Corallo]

Alan Mackenzie <acm@muc.de> writes:

> Hello, Andrea.
>
> On Sat, Dec 04, 2021 at 19:22:02 +0000, Andrea Corallo wrote:
>> Alan Mackenzie <acm@muc.de> writes:
>
> [ .... ]
>
>> Hi Alan,
>
>> > For extending emit_EQ, I've got the following embryonic scheme:
>
>> > 1/- Import the C variable symbols_with_pos_enabled:
>
>> >  gcc_jit_lvalue *syms_with_pos_enabled =
>> >                gcc_jit_context_new_global
>> >                  (comp.ctxt, NULL,
>> >                   GCC_JIT_GLOBAL_IMPORTED,
>> >                   gcc_jit_get_type (comp.ctxt, GCC_JIT_TYPE_BOOL),
>> >                   "symbols_with_pos_enabled");
>
>> Yep something like.  PS We already have 'comp.bool_type' to use.
>
> [ .... ]
>
>> > Can you let me know what you think of this approach, please?  That is,
>> > before I put a lot of work into it.  Is it broadly a good way of doing
>> > the job?
>
>> I think it could be a good idea but I believe there's no need to use
>> macros here, we could have just functions return rvalues no?
>
> Yes, no macros needed.  :-)
>
>> I'm not a big fan of C macros and I try not to use them whem possible.
>
> [ .... ]
>
> I have a problem at the moment, which could be a big problem.  How do I
> refer to a Lisp variable from jit generated code?
>
> In particular, I need read-access to symbols-with-pos-enabled, or more
> precisely to globals.f_symbols_with_pos_enabled.
>
> The gcc jit product seems to go out of its way to make such access as
> difficult as possible.  There is a way to get an integer out of "C space"
> into the jit mechanism, but this cannot be cast to a pointer type, and
> there is no similar mechanism to get a pointer out of C space.  In fact,
> gcc jit seems to restrict the language it supports to the equivalent of
> Pascal, and makes pointer arithmetic impossible.
>
> I tried declaring "globals" as a global variable to be imported into jit
> space, but the loader doesn't know about "globals".
>
> So, how can I get access to globals.f_symbols_with_pos_enabled?
>
> Thanks in advance!


Hi Alan,

I think the way should be done is that one declare in the .eln a global
variable as a (bool *), say 'f_symbols_with_pos_enabled_ref'.  Then
during eln load time we set into that the correct address of
'globals.f_symbols_with_pos_enabled' so it can be used as
'*f_symbols_with_pos_enabled_ref' by the generated code.

We do something very similar for the Emacs global var 'current_thread'.
In the eln we have a global variable named "current_thread_reloc" where
we store the address of 'current_thread'.  You can see we set this value
during eln load in 'load_comp_unit'.

Just grep CURRENT_THREAD_RELOC_SYM and you should find the relevant
pieces of code you are interested in.

Best Regards

  Andrea