Re: [Buildroot] [PATCH v2 2/4] package/gcc: use binutils wrappers for target libs

["Yann E. MORIN" <yann.morin.1998@free.fr>]

Nrobert, All,

On 2020-10-18 00:17 +0200, Norbert Lange spake thusly:
> This will use gcc-ar, gcc-nm and gcc-ranlib instead of the
> normal binutils tools. The difference is that with the
> wrappers, gcc plugins will be automatically picked up,
> which might be necessary with some flags.
> 
> Signed-off-by: Norbert Lange <nolange79@gmail.com>
> ---
> v1->v2:
> *   Only set those wrappers if gc 4.7 or newer
> ---
>  package/gcc/gcc.mk | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/package/gcc/gcc.mk b/package/gcc/gcc.mk
> index 114c2887a0..a24ffe3ee2 100644
> --- a/package/gcc/gcc.mk
> +++ b/package/gcc/gcc.mk
> @@ -99,6 +99,9 @@ GCC_COMMON_TARGET_CFLAGS += -Wno-error
>  endif
>  
>  # Propagate options used for target software building to GCC target libs
> +ifeq ($(BR2_TOOLCHAIN_GCC_AT_LEAST_4_7),y)
> +HOST_GCC_COMMON_CONF_ENV += AR_FOR_TARGET=gcc-ar NM_FOR_TARGET=gcc-nm RANLIB_FOR_TARGET=gcc-ranlib

So we were a bit skeptical about this one.

First, we believe that only the final gcc should be using those. Indeed,
we do not need much of the initial gcc, except libgcc.a, which anyway
gets overwitten by the final gcc, so we do not care that the libgcc.a is
built with LTO (and thus the gcc wrappers).

Second, gcc initial is only used to build glibc, and as your patch 4
states, glibc must not be built with LTO, we we also do not care that
the initial gcc uses its wrappers to build libgcc.

Third, shouldn't we be using the tupple-prefixed wrappers? Or does it
just happens that gcc will internally add its build directory to PATH so
that it can find the un-prefixed just-built ones?

For that last point, I added gcc-ar, gcc-nm, and gcc-ranlib in my PATH,
that are just simple wrapper scripts that trace their being called, and
then call to the actual gcca-r et al.:

    #!/bin/sh
    me="${0}"
    my_name="${0##*/}"
    found=false
    for i in $(which -a "${my_name}"); do
        if [ "${i}" -ef "${me}" ]; then
            found=true
        elif ${found}; then
            me="${i}"
        fi
    done
    if ! ${found}; then
        exit 42
    fi
    printf "YEM: wrapped %s\n" "${me}"
    exec "${me}" "${@}"

Turns out that the 'YEM: wrapped' string occurs nowhere in the build
directory (so it does not end up in config.log or whatever), and it
does not even appear on the stdout/stderr either.

So I am wondering how we can exercise these... Any hint?

Regards,
Yann E. MORIN.

> +endif
>  HOST_GCC_COMMON_CONF_ENV += CFLAGS_FOR_TARGET="$(GCC_COMMON_TARGET_CFLAGS)"
>  HOST_GCC_COMMON_CONF_ENV += CXXFLAGS_FOR_TARGET="$(GCC_COMMON_TARGET_CXXFLAGS)"
>  
> -- 
> 2.28.0

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