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notes on JIT internals

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svn: r12447
This commit is contained in:
Matthew Flatt 2008-11-14 14:33:23 +00:00
parent c4cdaf3c53
commit 0f8e31d0a2
1 changed files with 28 additions and 0 deletions
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28
src/mzscheme/src/jit.c
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@ -944,6 +944,34 @@ int check_location;
#define mz_retain(x) mz_retain_it(jitter, x)
#define mz_remap(x) mz_remap_it(jitter, x)
/*
mz_prolog() and mz_epilog() bracket an internal "function" using a
lighter-weight ABI that keeps all Rx and Vx registers as-is on
entry and exit. Some of those functions are registered in a special
way with add_symbol() so that the backtrace function can follow the
lightweight ABI to get back to the calling code. The lightweight
ABI does not support nested calls (at least not on all platforms;
see LOCAL2 below).
LOCAL2 and LOCAL3 are available for temporary storage on the C
stack using mz_get_local() and mz_set_local() under certain
circumstances:
* They can only be used within a function (normally corresponding
to a Scheme lambda) where mz_push_locals() has been called after
jit_prolog(), and where mz_pop_locals() is called before
jit_ret().
* On some platforms, LOCAL2 and LOCAL3 are the same.
* On some platforms, a lightweight function created with
mz_prolog() and mz_epilog() uses LOCAL2 to save the return
address. On those platforms, though, LOCAL3 is dufferent from
LOCAL2. So, LOCAL3 can always be used for temporary storage in
such functions (assuming that they're called from a function that
pushes locals, and that nothing else is using LOCAL2).
*/
#ifdef MZ_USE_JIT_PPC
/* JIT_LOCAL1, JIT_LOCAL2, and JIT_LOCAL3 are offsets in the stack frame. */
# define JIT_LOCAL1 56