Re: PATCH: PR binutils/12280: Makefiles don't support LTO

[Ralf Wildenhues <Ralf dot Wildenhues at gmx dot de>]

Hello H.J.,

* H.J. Lu wrote on Thu, Dec 02, 2010 at 06:34:56AM CET:
> This patch adds + to LINK in Makefile for GNU make.  OK for trunk?

> diff --git a/config/gnumake.m4 b/config/gnumake.m4
> new file mode 100644
> index 0000000..2d21e12
> --- /dev/null
> +++ b/config/gnumake.m4
> @@ -0,0 +1,22 @@
> +dnl Placed after AC_OUTPUT to add `+' to LINK for GNU make.

That is not reliable: a config.status run updating Makefile may be
triggered from make rules, by-passing configure completely.

Also, $(LINK) is not the only link-related variable, there can be
prog_LINK for programs and libraries.

The common way to do this is to have a new config.status action (which
however is also not recheck-safe) or to tack it onto the existing
Makefile action; e.g.:

AC_CONFIG_FILES([Makefile], [sed ... Makefile ...])

But why not go a different (and IMVHO simpler) route completely: have a
variable $(LTO) or so that expands to empty, or to '+' if LTO is used,
and then prepending that to *LINK values unconditionally.
That has the advantage that you can still get 'make -n' right if using
GNU make but not LTO.

Thanks,
Ralf

> +AC_DEFUN([GCC_CHECK_GNU_MAKE], [
> +  AC_CACHE_CHECK([whether make is GNU make],
> +		 gcc_cv_gnu_make, [
> +    GNU_MAKE=${MAKE-make}
> +    case `$GNU_MAKE -v 2>&1` in
> +    *GNU*Make*)
> +      gcc_cv_gnu_make=yes
> +      ;;
> +    *)
> +      gcc_cv_gnu_make=no
> +      ;;
> +    esac])
> +  if test "$gcc_cv_gnu_make" = "yes" ; then
> +    if test -f Makefile; then
> +      tmpmakefile=Makefile.$$
> +      sed -e "s/^LINK = \\$/LINK = +$/" Makefile > $tmpmakefile
> +      mv $tmpmakefile Makefile
> +    else
> +      AC_MSG_ERROR([Makefile doesn't exist])
> +    fi
> +  fi])