make install fail on cross-compile

[Adhemerval Zanella]

(Resending since I sent earlier to just Paul).

On 10/06/2020 04:49, Paul via Libc-help wrote:
> Building on x86_64-pc-linux-gnu for a cross-compile and
> target machine is also x86_64-pc-linux-gnu (but a later
> kernel).
> 
> Configured with
> 
>  cd glibc-build
>  ../glibc-2.31/configure --prefix=~/glibc-out ... --host=x86_64-pc-linux-gnu --enable-kernel=5.4.45
> 
> Make runs fine but hits a problem with make install:
> 
>  FATAL: kernel too old
>  Makefile:115: recipe for target 'install-symbolic-link' failed
>  make[1]: *** [install-symbolic-link] Aborted (core dumped)
> 
> My build kernel is only 4.15.0 but that shouldn't matter, seems
> that configure decided I was not doing a cross-compile,
> apparently because the build and host system types are the same.
> 
> config.log has:
> 
>  host='x86_64-pc-linux-gnu'
>  build='x86_64-pc-linux-gnu'
>  cross_compiling='no'
> 
> The relevant bit of the Makefile appears to be
> 
>  # Create links for shared libraries using the `ldconfig' program if possible.
>  # Ignore the error if we cannot update /etc/ld.so.cache.
>  ifeq (no,$(cross-compiling))
>  ifeq (yes,$(build-shared))
>  install: install-symbolic-link
>  .PHONY: install-symbolic-link
>  install-symbolic-link: subdir_install
>          $(symbolic-link-prog) $(symbolic-link-list)
>          rm -f $(symbolic-link-list)
> 
> The configure script:
> 
>  cross_compiling=no
>  ...
>  # FIXME: To remove some day.
>  if test "x$host_alias" != x; then
>    if test "x$build_alias" = x; then
>      cross_compiling=maybe
>    elif test "x$build_alias" != "x$host_alias"; then
>      cross_compiling=yes
>    fi
>  fi

This in fact came from autoconf (lib/autoconf/general.m4) while
expanding:

configure.ac:

  52 AC_SUBST(cross_compiling)

So one solution might to fix on autoconf (although there is no new
release since 2012, so it might not a feasible solution).

> 
> Well, if I configure and then edit config.make to change
> 
>  cross-compiling = no
> 
> to
> 
>  cross-compiling = yes
> 
> then make and make install runs fine and I get everything I
> want in ~/glibc-out which I can then copy to my target
> machine.
> 
> Is there a magic configure command line option to say that
> I really want to cross-compile?

What you might do is do not set --build= so cross_compiling is set to 
'maybe'. But I think the long term solution is to refactor the kernel
check ('FATAL: kernel too old') that prevents running binaries with
--enable-kernel=x.y.z on older kernels.

I recall Joseph has stirred some discussion about it, I need to track
down the discussion on libc-alpha.