Re: Patch: Add a stop bit in alignment for alloc.

[Jim Wilson <wilson at specifixinc dot com>]

On Tue, 2004-03-02 at 12:36, H. J. Lu wrote:
> 	* config/tc-ia64.c (align_frag): New.
> 	(md_assemble): Set the tc_frag_data field in align_frag for
> 	IA64_OPCODE_FIRST instructions.
> 	(ia64_md_do_align): Set align_frag.
> 	(ia64_handle_align): Add a stop bit if needed.

This looks good to me.

However, I don't think it is fool proof.  When we create an
rs_align_code frag, we call frag_align_code, which calls frag_var, which
calls frag_grow with the requested alignment - 1.  If there is no room
left in this obstack, then frag_grow will create a new frag.  So in some
cases, the alignment frag will be the one after align_frag.

There is also a loop in frag_grow which implies that the alignment frag
could be arbitrarily later, however, it isn't clear to me why the loop
is there.  So it looks like in rare cases the alignment frag could be
two after align_frag, and maybe in even rarer cases it could be farther.

In order to handle this, I think we need a loop to search forward from
align_frag to find the real alignment frag.  The first frag starting
from align_frag that has rs_align_code is the alignment frag.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com