Re: [PATCH] configure: Avoid using strings binary

[Peter Maydell <peter.maydell@linaro.org>]

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?



> ---
>  configure | 33 ++++++++++++++++++---------------
>  1 file changed, 18 insertions(+), 15 deletions(-)
>
> diff --git a/configure b/configure
> index 45ee6f4eb3..91e04635cb 100755
> --- a/configure
> +++ b/configure
> @@ -1426,27 +1426,30 @@ fi
>  # ---
>  # big/little endian test
>  cat > $TMPC << EOF
> -#include <stdio.h>
> -short big_endian[] = { 0x4269, 0x4765, 0x4e64, 0x4961, 0x4e00, 0, };
> -short little_endian[] = { 0x694c, 0x7454, 0x654c, 0x6e45, 0x6944, 0x6e41, 0, };
> -int main(int argc, char *argv[])
> -{
> -    return printf("%s %s\n", (char *)big_endian, (char *)little_endian);
> -}
> +#if defined(__BYTE_ORDER) && __BYTE_ORDER == __BIG_ENDIAN || \
> +    defined(__BIG_ENDIAN__)
> +# error BIG
> +#endif
> +int main(void) { return 0; }
>  EOF
>
>  if compile_prog ; then
> -    if strings -a $TMPE | grep -q BiGeNdIaN ; then
> -        bigendian="yes"
> -    elif strings -a $TMPE | grep -q LiTtLeEnDiAn ; then
> -        bigendian="no"
> -    else
> -        echo big/little test failed
> -        exit 1
> -    fi
> +  bigendian="yes"
>  else
> +  cat > $TMPC << EOF
> +#if defined(__BYTE_ORDER) && __BYTE_ORDER == __LITTLE_ENDIAN || \
> +    defined(__LITTLE_ENDIAN__)
> +# error LITTLE
> +#endif
> +int main(void) { return 0; }
> +EOF
> +
> +  if compile_prog ; then
> +    bigendian="no"
> +  else
>      echo big/little test failed
>      exit 1
> +  fi
>  fi

thanks
-- PMM