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

[Nathanael Nerode <neroden at twcny dot rr dot com>]

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.

> 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...

> Do pathnames from this search ever get embedded into GCC?  If so it
> probably needs to be broken up into two searches.
I should check that.  It's hard to check.

I certainly want to separate tests of the build->target assembler, used 
for building libgcc2, from tests of the host->target assembler, used to 
determine the behavior of the newly built gcc.  Those two things 
shouldn't be confounded (although one should *default* from the other if 
build=host -- I've concluded that that's the clean way to write such 
things).

Thanks for your help.

--Nathanael