Re: [Lightning] Porting GNU Smalltalk to lightning 2

[Holger Hans Peter Freyther]

On Sun, Oct 26, 2014 at 03:17:11PM -0200, Paulo César Pereira de Andrade wrote:

>   I created the reverse hash to simulate the above, after finding that code
> that did store a nativeCode* could change it to another one (so I could
> not play smart and store a pointer to a method_entry pointer, and then
> just dereference the nativeCode pointer when needing it).
>    Storing the method_entry somewhere in the jit code is possible, could
> be a jump over the value stored (ugly), a function in the jit that would
> return the method_entry associated with it (complicated), so, a
> naive/simple solution for now is the reverse hash table. But other
> kinds of optimizations could be done.

Ah thanks for the explanation. Okay we have the start of the code pointer
and we want to find the method_entry it refers to. I know you mentioned it
already but could you re-iterate why we can't have a "reservation" in front
of the native code generated by lightning?


 jit_pointer_t
-_jit_emit(jit_state_t *_jit)
+_jit_emit(jit_state_t *_jit, size_t offset )
 {
     jit_pointer_t       code;
     jit_node_t         *node;
@@ -1859,10 +1859,11 @@ _jit_emit(jit_state_t *_jit)
 #if defined(__sgi)
        mmap_fd = open("/dev/zero", O_RDWR);
 #endif
-       _jit->code.ptr = mmap(NULL, _jit->code.length,
+       _jit->code.ptr = mmap(NULL, _jit->code.length + offset,
                              PROT_EXEC | PROT_READ | PROT_WRITE,
                              MAP_PRIVATE | MAP_ANON, mmap_fd, 0);
        assert(_jit->code.ptr != MAP_FAILED);
+       _jit->code.ptr += offset;
     }
     _jitc->code.end = _jit->code.ptr + _jit->code.length -
        jit_get_max_instr();
@@ -1879,6 +1880,7 @@ _jit_emit(jit_state_t *_jit)
            }
            if (_jit->user_code)
                goto fail;
+#error "add the offset everywhere"


this doesn't look too awful? Does it?