[Buildroot] [PATCH 18/18] erlang: make libatomic_ops optional

[Thomas Petazzoni <thomas.petazzoni@free-electrons.com>]

Frank,

On Fri, 22 Jan 2016 20:11:11 -0500, Frank Hunleth wrote:
> The Erlang developers prefer the use of Erlang's native atomics in
> Erlang 18. In the previous Erlang release, the native atomics
> implementation was not complete and so libatomic_ops was necessary. Now
> libatomic_ops is used as a fallback, but based on tests of every
> qemu_*_defconfig and several other configs it appears to not be
> necessary. In fact, it causes build failures on aarch64. Since it is

If using libatomic_ops on aarch64 with erlang causes build failures,
then your BR2_PACKAGE_ERLANG_USE_LIBATOMIC_OPS option should depend
on !BR2_aarch64.

> conceivable that a platform exists that may still require libatomic_ops,
> this change makes the use of the library optional.
> 
> Fixes:
> http://autobuild.buildroot.net/results/0cd/0cd22eb74fa29e5a85bf897762e16ab3daf33962/
> 
> Signed-off-by: Frank Hunleth <fhunleth@troodon-software.com>
> ---
>  package/erlang/Config.in | 10 ++++++++--
>  package/erlang/erlang.mk |  2 ++
>  2 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/package/erlang/Config.in b/package/erlang/Config.in
> index 0ec01bb..9bd64ac 100644
> --- a/package/erlang/Config.in
> +++ b/package/erlang/Config.in
> @@ -7,8 +7,7 @@ config BR2_PACKAGE_ERLANG
>  	bool "erlang"
>  	depends on BR2_USE_MMU # fork()
>  	depends on !BR2_STATIC_LIBS
> -	depends on BR2_PACKAGE_LIBATOMIC_ARCH_SUPPORTS
> -	select BR2_PACKAGE_LIBATOMIC_OPS
> +	depends on BR2_PACKAGE_LIBATOMIC_ARCH_SUPPORTS # erlang native atomics and libatomic_ops

This shouldn't be here, since you no longer select libatomic_ops.

>  	help
>  	  Erlang is a programming language used to build massively scalable
>  	  soft real-time systems with requirements on high availability.
> @@ -20,6 +19,13 @@ config BR2_PACKAGE_ERLANG
>  
>  if BR2_PACKAGE_ERLANG
>  
> +config BR2_PACKAGE_ERLANG_USE_LIBATOMIC_OPS

We rarely use _USE_ in Config.in options for such cases. Just
BR2_PACKAGE_ERLANG_LIBATOMIC_OPS is enough.

> +	bool "use libatomic_ops"
> +	select BR2_PACKAGE_LIBATOMIC_OPS

This is where you should have the
"depends on BR2_PACKAGE_LIBATOMIC_ARCH_SUPPORTS".

> +	help
> +	  Erlang's native atomic ops implementation is preferred. If this is
> +	  insufficient, enabling this option forces Erlang to use libatomic_ops.

Lines too long I believe.

> +
>  config BR2_PACKAGE_ERLANG_SMP
>  	bool "enable SMP support"
>  	help
> diff --git a/package/erlang/erlang.mk b/package/erlang/erlang.mk
> index dfab30d..a2f75e7 100644
> --- a/package/erlang/erlang.mk
> +++ b/package/erlang/erlang.mk
> @@ -30,8 +30,10 @@ ERLANG_CONF_ENV += erl_xcomp_sysroot=$(STAGING_DIR)
>  
>  ERLANG_CONF_OPTS = --without-javac
>  
> +ifeq ($(BR2_PACKAGE_ERLANG_USE_LIBATOMIC_OPS),y)
>  ERLANG_DEPENDENCIES += libatomic_ops
>  ERLANG_CONF_OPTS += --with-libatomic_ops=$(STAGING_DIR)/usr LIBS=-latomic_ops
> +endif

Can you add a "else" clause to explicitly disable libatomic_ops
support? Otherwise, libatomic_ops may be enabled in the Buildroot
configuration, built before erlang, and detected automatically by
erlang configure script.

Thanks,

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com