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

Nathanael Nerode neroden@twcny.rr.com
Fri Mar 14 19:45:00 GMT 2003


Daniel Jacobowitz wrote:
> 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.

Of course.  My point was that getting rid of the version number checks 
is undesirable because they're actually the best way of getting 
information in a particular setup.  Ick, but true.

--Nathanael



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