Re: [PATCH]: Separate target and host config files

[Nathan Sidwell <nathan at codesourcery dot com>]

Zack Weinberg wrote:
> Nathan Sidwell <nathan@codesourcery.com> writes:
>
>
> > This patch fixes the problem by adding a new 'tconfig.in' template and
> > amending the configure machinery to create auto-target.h from that, and
> > inlude that file in 'tconfig.h'.  This allowed me to remove the #include
> > auto-host.h from the target side libraries.  I also uncovered a couple
> > of typos with the runtime checking configure processing.
>
>
> If I understand the patch correctly, the definitions in auto-target.h
> are a strict subset of the definitions in auto-host.h.  I'm not sure I
> see the point.  Is it merely that some of those definitions are unsafe
> to expose to target libraries?  If so, could you illustrate why?

Correct they are a subset.  However, auto-host also contains such
delights as BYTEORDER, CHAR_BIT, and various type #defines like
ssize_t.  It seems dangerous to expose more than the minimum necessary
to the target-side files.  The current situation of just including
auto-host.h where it is absolutely needed is not practical going
forward, as essentially all target side files include tsystem.h, which
now provides definitions for runtime gcc_assert and gcc_unreachable.
It requires ENABLE_RUNTIME_CHECKING to know what those should expand
to.

> Also, again if I understand correctly, I'd prefer that the subsetting
> be done not by configure, but by a separate operation controlled from
> the Makefile, e.g. by adding more special-case logic to mkconfig.sh
> for tconfig.h.  This is primarily because I don't trust autoheader not
> to decide it knows better, and splat a complete copy of config.in onto
> tconfig.in, ruining all your careful subsetting.

The subsetting is done manually, by manually editing the template file
tconfig.in (as it says in the comment therein).  autoheader will only
autogenerate the _first_ template mentioned in AC_CONFIG_HEADERS, as
autoheader's documentation states.  In this case that will remain
config.in.

An alternative mechanism for creating auto-target.h would be to
grep auto-host.h for the desired #defines.  But this strikes me as
reinventing the wheel -- autoconf already has machinery to generate
a header file from a template, and that's what I've employed.

> Also also, could we please *not* increase the number of thing.in files
> with a confusing name relationship to their thing.h?  Call it
> auto-target.in if it must exist.

yeah, I was in a quandry about that, and I had originally named it
as you suggest.  But, that then makes it inconsistent with the current
mapping of config.in->auto-host.h.  IMHO having a similar mapping
to that was more desireable -- but there wasn't much in it :)  Perhaps
we should take the opportunity of renaming config.in to auto-host.in
and removing that confusion too!  If we do that, I'd prefer to address
it as a separate patch.

Let me know how you'd like to proceed

nathan

--
Nathan Sidwell    ::   http://www.codesourcery.com   ::     CodeSourcery LLC
nathan@codesourcery.com    ::     http://www.planetfall.pwp.blueyonder.co.uk