Re: bug#51144: GNU grep 3.7 fails to build on FreeBSD

[Alexey Dokuchaev via Gnulib discussion list <bug-gnulib@gnu.org>]

On Thu, Oct 14, 2021 at 10:34:55AM -0700, Paul Eggert wrote:
> On 10/14/21 7:02 AM, Alexey Dokuchaev wrote:
> > On Wed, Oct 13, 2021 at 11:47:34AM -0700, Paul Eggert wrote:
> > > On 10/12/21 9:02 PM, Alexey Dokuchaev wrote:
> > > > Ports framework does several things which affect GNU configure
> > > > scripts, particularly, it replaces build-aux/config.guess file
> > > > with our own, where host/build tuples are derived from.
> > > > 
> > > > x86_64 is spelled as amd64 in FreeBSD
> > > 
> > > Ouch. When porting, does this mean you need to look for places where
> > > GNU source code says "x86_64" and replace many of these places with
> > > "amd64" before building? That sounds error-prone.
> > 
> > No, of course not, typically we don't replace anything.  All we do is
> > use our pre-built templates for config.{guess,site,sub} and pass the
> > --build=amd64-portbld-freebsd$(version) argument to configure scripts
> > if they are generated by GNU autotools.
> 
> Surely this doesn't work if there's a configure.ac or m4/*.m4 file that
> does something like this:
> 
>   if "$host_os" = x86_64; then
>     ...
>   fi
> 
> and I see examples of this in gnulib/m4's float_h.m4, host-cpu-c-abi.m4,
> lib-prefix.m4, multiarch.m4, printf.m4, stack-direction.m4. In general
> don't you need to also edit these files and re-run Autoconf?

In general, we don't edit those files, and typically we only run autoconf
when there's no pre-generated configure script, or there's something so
very wrong about it, or generated Makefiles, that patching isn't feasible
and we have to rebootstrap the whole thing.

About why this x86_64 vs amd64 thing does not cause massive fallout for
us, I better ask our Autotools expert.  Tijl, can you shed some light
here?  I've added back omitted context to the quoted parts of this email,
I hope Paul wouldn't mind.

./danfe

> > I can't remember when was the last time I've been bitten by this. :-)
> 
> Often Gnulib code will guess the right value anyway. Not always, though.
> You ran into a case where Gnulib didn't guess and aborted. Some other
> times, the guess may differ from what it would be if you did a plain
> 'configure; make' from a tarball. You might want to test for that, given
> the above list of potential problem files.
> 
> There may well be similar problems in configure.ac or *.m4 files
> maintained in GNU projects other than Gnulib. Autoconf itself has
> "x86_64" hardwired into AC_C_BIGENDIAN; I don't know whether this
> affects FreeBSD compilers.