...

...

#define cond_extern(name) asm(".weak\t" #name "\n\t.set\t" #name ", unimpl_extern")

I do not understand what this does. Does it work?

Yes, it does. See file: gcc.info, node: Function Attributes, section: 5.24 Declaring Attributes of Functions

...

...

static int unimpl_extern(void) { return -ENOSYS; /* or something more appropriate */ }

How is this different that using the dummy function?

The main difference is that with "normal" functions you must make sure that the dummy function does not get compiled / linked when you implement a real function. "Weak" are simply overwritten if any user provides another (real) function with the same name. No #ifdef mess any more :-)

So in practice, it would look something like this?:

void jumptable_init (void) { int i;

gd->jt = (void **) malloc (XF_MAX * sizeof (void *)); for (i = 0; i < XF_MAX; i++) gd->jt[i] = (void *) dummy;

#define EXPORT_FUNC(name) asm(".weak\t" #name "\n\t.set\t" #name ", dummy"); #include <_exports.h> #undef EXPORT_FUNC

gd->jt[XF_get_version] = (void *) get_version; gd->jt[XF_malloc] = (void *) malloc; gd->jt[XF_free] = (void *) free; gd->jt[XF_getenv] = (void *) getenv; gd->jt[XF_setenv] = (void *) setenv; gd->jt[XF_get_timer] = (void *) get_timer; gd->jt[XF_simple_strtoul] = (void *) simple_strtoul; gd->jt[XF_udelay] = (void *) udelay; gd->jt[XF_install_hdlr] = (void *) irq_install_handler; gd->jt[XF_free_hdlr] = (void *) irq_free_handler; gd->jt[XF_i2c_write] = (void *) i2c_write; gd->jt[XF_i2c_read] = (void *) i2c_read; ........

}

it could't really be that simple, could it? I bet my sintax is wrong, and I still do not compleatly understand how the compiler intreprets "weak" and "set". But I can see how this would work.

-Jeff