[Buildroot] [PATCH] gcc/gcc-final: pass TARGET_CFLAGS flags to configure with --enable-cxx-flags

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

Max, All,

On 2015-06-01 17:37 +0300, Max Filippov spake thusly:
> Currently only TARGET_ABI flags are passed to the final compiler
> configure script and only when building for Xtensa. Since libstdc++ is a
> normal library it should be built with full TARGET_CFLAGS on all
> targets.
> 
> Pass TARGET_CFLAGS flags to gcc-final configure script for all targets
> in the --enable-cxx-flags parameter.
> 
> Suggested-by: Arnout Vandecappelle <arnout@mind.be>
> Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

So, I finally had a look at this patch. I've tested it to build a
gcc-4.9 + glibc-2.21 + binutils-2.24 toolchain with C++ support, which
then was used to suessfully build Qt5base (which is quite a heavy C++
user).

However, I'd like to understand what this is all about.

In gcc.mk, we do:

    GCC_COMMON_TARGET_CXXFLAGS = $(TARGET_CXXFLAGS)
    [...]
    HOST_GCC_COMMON_CONF_ENV += CXXFLAGS_FOR_TARGET="$(GCC_COMMON_TARGET_CXXFLAGS)"

So it looks like we were already passing the proper CXXFLAGS to gcc (we
only filter-out problematic flags, like -Os on broken gcc-4.5 for PPC).

So, what are we supposed to gain/loose with this change?

As a side note, we should not have to pass TARGET_ABI either, since it
is part of TARGET_CFLAGS and as shown above, it is already part of the
CFLAGS_FOR_TARGET that we pass gcc.

Any explanations? Something that I missed?

Regards,
Yann E. MORIN.

> ---
>  package/gcc/gcc-final/gcc-final.mk | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/package/gcc/gcc-final/gcc-final.mk b/package/gcc/gcc-final/gcc-final.mk
> index 8d7009b..59c8708 100644
> --- a/package/gcc/gcc-final/gcc-final.mk
> +++ b/package/gcc/gcc-final/gcc-final.mk
> @@ -185,8 +185,6 @@ endef
>  HOST_GCC_FINAL_POST_INSTALL_HOOKS += HOST_GCC_FINAL_INSTALL_USR_LIBS
>  endif
>  
> -ifeq ($(BR2_xtensa),y)
> -HOST_GCC_FINAL_CONF_OPTS += --enable-cxx-flags="$(TARGET_ABI)"
> -endif
> +HOST_GCC_FINAL_CONF_OPTS += --enable-cxx-flags="$(TARGET_CFLAGS)"
>  
>  $(eval $(host-autotools-package))
> -- 
> 1.8.1.4
> 
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