cross compile and checking for C compiler default output file name

[Josef Wolf]

On Thu, Jan 14, 2010 at 02:19:53PM +0100, Josef Wolf wrote:
> Hello,
> 
> In newlib-1.15.0, the following hunk had been added to
> libgloss/m68k/configure.in
> 
>  @@ -81,7 +43,29 @@
>   LD=${LD-ld}
>   AC_SUBST(LD)
>   AC_PROG_RANLIB
>  +LIB_AM_PROG_AS
>   
>  +AC_MSG_CHECKING([target cpu family])
>  +DO=m68k
>  +dnl Temporarily modify LDFLAGS so that link tests will succeed without
>  +dnl a C library.  Note that we may not have a C librabry yet and that
>  +dnl autoconf automatically adds script to check whether we can create
>  +dnl an executable or not.
>  +dnl
>  +saved_LDFLAGS="$LDFLAGS"
>  +LDFLAGS="-nostdlib -e main"
>  +AC_PREPROC_IFELSE([#ifndef __mcoldfire__
>  +               #error we are not coldfire
>  +               #endif],
>  +              DO="cf",)
>  +AC_PREPROC_IFELSE([#ifndef __mfido__
>  +               #error we are not fido
>  +               #endif],
>  +              DO="fido",)
>  +LDFLAGS=$saved_LDFLAGS
>  +AC_MSG_RESULT($DO)
>  +AC_SUBST(DO)
>  +
>   host_makefile_frag=${srcdir}/../config/default.mh
>   target_makefile_frag=${srcdir}/../config/default.mt
>   
> 
> This causes the configure script to fail when building newlib for a cross
> compiler, since cross compiler do _not_ create executables. Here's the
> error message:
> 
>  configure:2336: checking for C compiler default output file name
>  configure:2339: m68k-coff-gcc -B/var/tmp/builds/crossgcc/build/newlib/m68k-coff/m68000/newlib/ -isystem /var/tmp/builds/crossgcc/build/newlib/m68k-coff/m68000/newlib/targ-include -isystem /var/tmp/builds/crossgcc/src/newlib-1.15.0/newlib/libc/include  -m68000 -nostdlib -e main conftest.c  >&5
>  /tmp/ccWpP6Cn.o(.text+0x6):conftest.c: undefined reference to `__main'
>  collect2: ld returned 1 exit status
>  configure:2342: $? = 1
>  configure: failed program was:
>  | /* confdefs.h.  */
>  |
>  | #define PACKAGE_NAME ""
>  | #define PACKAGE_TARNAME ""
>  | #define PACKAGE_VERSION ""
>  | #define PACKAGE_STRING ""
>  | #define PACKAGE_BUGREPORT ""
>  | /* end confdefs.h.  */
>  |
>  | int
>  | main ()
>  | {
>  |
>  |   ;
>  |   return 0;
>  | }
>  configure:2381: error: C compiler cannot create executables
>  See `config.log' for more details.
> 
> This is detected wrong, since my (cross-) compiler _can_ create working
> executables, at least with newslib-1.14.0.
> 
> Any hints how to work around this problem?

Does really nobody know why this check is done? Or is newlib not supposed to
be used for cross compiling?