Re: autoconf-2.61's AC_LINK_IFELSE with MinGW cross-compilers

[Stepan Kasal]

Hello,

let me return to the problem reported on Thu, Mar 29, 2007 by Chris Johns:

> The autoconf-2.61 release added a 'test -x' to AC_LINK_IFELSE and that has 
> broken MinGW based cross-compilers using autoconf packages in MSYS.
> 
> The change is:
> 
> http://cvs.savannah.gnu.org/viewcvs/autoconf/lib/autoconf/general.m4?root=autoconf&r1=1.931&r2=1.932

the changelog entry is:

2006-10-04  Paul Eggert  <address@hidden>

        (_AC_LINK_IFELSE): Test that resulting file is executable.
        Problem reported by mwoehlke in
        <http://lists.gnu.org/archive/html/bug-coreutils/2006-10/msg00048.html>.

I think we shall make a note in the comment above _AC_LINK_IFELSE,
e.g.:

# Test that resulting file is executable; see the problem reported by mwoehlke
# in <http://lists.gnu.org/archive/html/bug-coreutils/2006-10/msg00048.html>.

> RTEMS uses AC_LINK_IFELSE and MinGW cross-compilers fail this test.
> 
> A MinGW compiler cannot set an execute bit on an executable as Windows 
> provides no support for it. MSYS emulates the execute bit by pattern 
> matching the file extension (.exe, .bat, .com) so a native Windows compiler 
> creating a a.exe file works. Here AC_PROG_CC sets $ac_exeext to '.exe' and 
> AC_LINK_IFELSE creates a .exe file. A MinGW cross-compiler such as one for 
> RTEMS by default creates 'a.out' so $ac_exeext is ''.
> 
> Is the 'test -x' suitable for MSYS and a cross-compiler ?

Indeed, it seems that this combination is not healthy.

There does not seem to be a suitable replacement for the 'test -x'
which would work universally.
And the GNU-on-Woe32 community has not submitted a code which would
tell us when 'test -x' should be avoided.

But we can pick the third condition of this combination: we might
skip the 'test -x' when cross-compiling.  The rationale being:

1) Whoever is trying to cross-compile, they usually know what they
are doing, so they can live with the less strict protection.
IOW, telling the configure where to find the cross-compiler is the
least of the cross-compiling skills.

2) The cross-compiler's output has to be ``moved'' (whatever that
means) before it can be executed.  So it sounds plausible that the
cross compiler might leave the output non-executable.

A proposed patch attached.  Yes, the change is not nice, but would it
hurt?

Comments welcome,
        Stepan Kasal

autoconf-20070411-cross-test-x.patch
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