On Mon, Sep 17, 2001 at 05:52:19PM -0400, Dan Sugalski wrote:
> >Which is really going to screw up backpatching. :(
>
> Maybe. I don't think it's as big a deal as you might think it is, since we
> vector through a register, and you can just patch the register load.
The reason I started looking at this was because the test suite contains
this:
skip( "label constants unimplemented in assembler", 1 );
set I4, 42
set I5, HERE
jump I5
set I4, 1234
HERE:
print I4
end
Since HERE isn't known when it's first encountered, we leave a space
for backpatching. But when we backpatch, to get it right, we need to
be aware that we're doing a set, and produce an absolute rather than
a relative address. This isn't easy. Especially since to make that
work, we need to know that the register will be used to do a jump and
not a branch. Consider:
set I5, WHEREVER
if I1, HERE, THERE
HERE: jump I5
THERE: branch I5
When we do the set, should WHEREVER be a relative or an absolute
address?
--
dd.c: sbrk(64); /* For good measure */
- plan9 has a bad day
