V2 [PATCH] PKG_CHECK_MODULES: Check if $pkg_cv_[]$1[]_LIBS works

[Mark Wielaard]

Hi,

On Mon, 2020-07-27 at 12:32 -0700, H.J. Lu via Binutils wrote:
> diff --git a/config/pkg.m4 b/config/pkg.m4
> index 13a8890178..45587e97c8 100644
> --- a/config/pkg.m4
> +++ b/config/pkg.m4
> @@ -147,6 +147,12 @@ AC_MSG_CHECKING([for $2])
>  _PKG_CONFIG([$1][_CFLAGS], [cflags], [$2])
>  _PKG_CONFIG([$1][_LIBS], [libs], [$2])
>  
> +dnl Check whether $pkg_cv_[]$1[]_LIBS works.
> +pkg_save_LDFLAGS="$LDFLAGS"
> +LDFLAGS="$LDFLAGS $pkg_cv_[]$1[]_LIBS"
> +AC_TRY_LINK([],[return 0;], [pkg_failed=no], [pkg_failed=yes])
> +LDFLAGS=$pkg_save_LDFLAGS
> +
>  m4_define([_PKG_TEXT], [Alternatively, you may set the environment
> variables $1[]_CFLAGS
>  and $1[]_LIBS to avoid the need to call pkg-config.
>  See the pkg-config man page for more details.])

This hunk seems wrong. You are testing whether the $pkg_cv_[]$1[]_LIBS
flags work, but they might be empty if the library wasn't found
(pkg_failed=yes). Then the AC_TRY_LINK will obviously succeed, and then
you set pkg_failed=no. But that indicates that the library was found.

Cheers,

Mark