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[Lightning] multiple states and multiple functions

From: Marco Maggi
Subject: [Lightning] multiple states and multiple functions
Date: Mon, 30 Jul 2007 20:51:13 +0200

Ciao (hi Ludovic),

  I am trying to learn the basics of GNU Lightning under
i686-pc-linux-gnu, GCC 3.4.2. As a full beginner I
would like signal that (maybe you know it already):

* with version 1.2  "lightning.h" is not installed by
  "make" (or at least that is the case if I use
  DESTDIR to install under a tmp directory);

* the docs talk about "struct jit_state", but "jit_state"
  it a typedef;

* I do not use Automake, and after lightiningize in
  "lightning.m4" there are still:


  I had to comment them out by hand (undocumented, is it
  safe to do it?).

It is not clear to me if it is possible to accumulate
code into a buffer from different C functions. I use
a dynamically allocated "jit_state" and I define:

#define _jit    data->state

where "data" is a struct with a "jit_state state" field.
I get segfaults that I cannot explain, some of them
because I am still learning, that is for sure, but one
is driving me crazy: is "jit_finish()" supposed to work
if I use it from a C function different from the one in
which I initialised the buffer and the "jit_state"? Is
the state in some way linked to the stack of the first
function in which it is used?

I ask this because when I try the printf example in the
documentation (that is a single function) everything
works; but If I build a dynamic function from multiple
C functions I get a segfault.

The code I am using is:

    /* Accumulate the code required to get an
       argument into R0. */
      unsigned long in;

      in = jit_arg_p();
      jit_getarg_p(JIT_R0, in);
    /* Does the call: the argument must be in R0 */
  jit_flush_code(data->buffer, jit_get_ip().ptr);

when I invoke the function: by printing log messages I
see that "scm_call_0()" is evaluated correctly and returns
(I tried different functions and they go on at least up
until the C "return") and then a segfault comes as if
there is a problem with fetching the return address
to jump back to the caller.


Marco Maggi

"Now feel the funk blast!"
Rage Against the Machine - "Calm like a bomb"

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