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Re: Bug#850329: autoconf tries to execute foreign binaries

From: Ben Pfaff
Subject: Re: Bug#850329: autoconf tries to execute foreign binaries
Date: Sun, 20 Aug 2017 23:21:55 -0700
User-agent: Mutt/1.5.23 (2014-03-12)

I'm adding the autoconf mailing list.  For more background, take a look
at the Debian bug log:

On Sun, Aug 20, 2017 at 09:18:44PM +0200, Vincent Lefevre wrote:
> On 2017-08-20 11:01:28 -0700, Ben Pfaff wrote:
> > This bug regards how Autoconf decides whether it's cross-compiling.
> > This is a somewhat tricky issue.  The following is summarized from
> >
> > (and quotes come from there):
> > 
> >    1. Without --host or --build, Autoconf aborts if it can't run the
> >       binaries that the compiler produces.  It assumes that's a
> >       problem in the system configuration, such as a broken
> >       compiler.
> > 
> >    2. With --host and --build, Autoconf decides that it's
> >       cross-compiling if the host and the build system are
> >       different.
> > 
> >           "If you specify both, and they're different, configure enters
> >           cross compilation mode, so it doesn't run any tests that
> >           require execution."
> > 
> >    3. With --host, but not --build, Autoconf decides that it's
> >       cross-compiling if it can't run a binary produced by the
> >       compiler:
> > 
> >           "If you specify --host, but not --build, when configure
> >           performs the first compiler test it tries to run an executable
> >           produced by the compiler. If the execution fails, it enters
> >           cross-compilation mode. This is fragile. Moreover, by the time
> >           the compiler test is performed, it may be too late to modify
> >           the build-system type: other tests may have already been
> >           performed."
> > 
> > The issue here is what Autoconf should do in case #3, which is what wine
> > is doing.  Is there a better way to detect whether the system can run a
> > binary, than to try to run the binary?  Or is there a way to avoid the
> > broken dash behavior?
> In case 3, can't Autoconf use the guessed value of BUILD, so that
> it would be like case 2?
> > But I am a little concerned about whether we should do anything at all,
> > because case #3 is deprecated:
> > 
> >     "**Do not rely on [case 3]**, as it will be removed in the near
> >     future...  Therefore, whenever you specify --host, be sure to
> >     specify --build too."
> As the --build value can be guessed, I think that it would be annoying
> for the user to force him to use --build in case of cross-compilation.
> IMHO, making case 3 like case 2 with the guessed value of BUILD (as
> I've proposed above) would make sense. That would be the typical case
> for cross-compilation, as in general, one builds on the machine where
> one runs configure.

Hmm.  I'm comfortable with the idea of trying to figure out some way to
avoid trying to execute binaries as if they were shell scripts.  On the
other hand, while I don't personally object to changing this basic
Autoconf behavior, this is getting well into the territory where I'd be
uncomfortable proposing it myself.  Does anyone on the autoconf mailing
list have thoughts?

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