[patch] Important comment update to gcc/configure.in

[Daniel Jacobowitz]

On Fri, Mar 14, 2003 at 02:34:14PM -0500, Nathanael Nerode wrote:
> Daniel Jacobowitz wrote:
> >On Fri, Mar 14, 2003 at 12:09:36AM -0500, Nathanael Nerode wrote:
> >
> >>I believe this is correct.  I want review only in case I got it wrong.
> >>
> >>This clarifies the important issue of *which* assembler and linker
> >>we are looking for -- it's not the BUILD->BUILD, BUILD->HOST, or 
> >>BUILD->TARGET assemblers (all of which might be used and different in
> >>a Canadian cross compile)... it's the HOST->TARGET one, which we can't
> >>always even execute.
> >>
> >>Now that I've got this clear, I believe I'll actually be able to clean
> >>up the related code.
> >
> >
> >Nope.  Couple of subtleties here, I think.  First of all, remember,
> >we're on BUILD right now.  We can not search for anything that's
> >supposed to live on HOST; it might not be there.  Secondly, we use this
> >assembler for feature tests, so we have to be able to execute it.
> Ah, but that's what the version checks are for. :-)  For when we are 
> building a brand new HOST->TARGET gas and can't run it.

That's not the interesting case.  Just because BUILD != HOST doesn't
imply we're building gas in-tree.  I never am.  I still need to get the
features somehow.

> >Generally we want a BUILD->TARGET assembler, and to make the assumption
> >that it will have the same features as the HOST->TARGET assembler.
> That's really confusing. :-)  That seriously needs to be documented, 
> since it's an undocumented assumption if BUILD!=HOST.
> 
> The fact is that the feature tests are used as if they were feature 
> tests for the HOST->TARGET assembler.  They determine the format of the 
> assembly output by the newly built gcc.  I *think* that's the only thing 
> they determine, but I'm not sure yet.
> 
> Because of this, in the build!=host case, the version number checks on 
> the newly built gas are actually *better*, more accurate tests, than the 
> feature checks, which are on a build->target assembler, which isn't the 
> assembler we're actually interested in.  It's an interesting situation, 
> certainly...

Except where they're impossible.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer