Re: [PATCH] configure: Avoid using strings binary

["Daniel P. Berrangé" <berrange@redhat.com>]

On Thu, Oct 13, 2022 at 11:39:34AM +0100, Peter Maydell wrote:
> On Thu, 13 Oct 2022 at 09:47, Michal Privoznik <mprivozn@redhat.com> wrote:
> >
> > When determining the endiandness of the target architecture we're
> > building for a small program is compiled, which in an obfuscated
> > way declares two strings. Then, we look which string is in
> > correct order (using strings binary) and deduct the endiandness.
> > But using the strings binary is problematic, because it's part of
> > toolchain (strings is just a symlink to
> > x86_64-pc-linux-gnu-strings or llvm-strings). And when
> > (cross-)compiling, it requires users to set the symlink to the
> > correct toolchain.
> >
> > Fortunately, we have a better alternative anyways. Since we
> > require either clang or gcc we can rely on macros they declare.
> >
> > Bug: https://bugs.gentoo.org/876933
> > Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
> 
> If we can determine this just by looking at C macros, does
> this really need to be a configure test at all ? Paolo?

We don't need to rely on CLang / GCC macros either, as this
is exposed by GLib 

$ grep BYTE_ORDER /usr/lib64/glib-2.0/include/glibconfig.h
#define G_BYTE_ORDER G_LITTLE_ENDIAN

IOW, any code that needs to know can do one of:

  #if G_BYTE_ORDER == G_LITTLE_ENDIAN

  #if G_BYTE_ORDER == G_BIG_ENDIAN


The only thing 'configure' seems to be doing with the 'bigendian'
env var it sets, is to construct a meson cross compiler spec

  if test "$cross_compile" = "yes"; then
    cross_arg="--cross-file config-meson.cross"
    echo "[host_machine]" >> $cross
    echo "system = '$targetos'" >> $cross
    case "$cpu" in
        i386)
            echo "cpu_family = 'x86'" >> $cross
            ;;
        *)
            echo "cpu_family = '$cpu'" >> $cross
            ;;
    esac
    echo "cpu = '$cpu'" >> $cross
    if test "$bigendian" = "yes" ; then
        echo "endian = 'big'" >> $cross
    else
        echo "endian = 'little'" >> $cross
    fi

so we do need a compile time test in configure, but I'd suggest
using G_BYTE_ORDER

With regards,
Daniel
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