[Buildroot] [PATCH v2 1/1] protobuf: fix detection of __atomic_*() built-ins

[Arnout Vandecappelle <arnout@mind.be>]

On 02/17/16 18:43, Carlos Santos wrote:
> - Use the recently introduced BR2_TOOLCHAIN_HAS_ATOMIC boolean.
> 
> - Import an upstream patch to fix error handling when atomic operations
>   are not detected. Without this patch the build fails due to a syntax
>   error instead of showing the proper message.
> 
> - Add a patch to configure.ac to check if libatomic is needed and force
>   linking to it (we will attempt to submit this upstream).
> 
> - Disable build for SPARC64 because it fails due to a missing definition
>   of Atomic64.
> 
> On PowerPC, the __atomic_*() built-ins for 1-byte, 2-byte and 4-byte
> types are available built-in. The corresponding built-ins for 8-byte
> types, however, are implemented via libatomic, so requiring gcc >= 4.8.
> 
> In Buildroot, to simplify things, it was decided to require gcc 4.8 as
> soon as the architectures has at least one __atomic_*() built-in variant
> that requires libatomic.
> 
> Since protobuf most likely only uses the 1, 2 and 4-byte variants, it
> *could* technically build with gcc 4.7. This is probably not a big deal,
> and we can live with requiring gcc 4.8 on PowerPC to build protobuf. The
> same restriction applies to SPARC.
> 
> The build for SPARC64 breaks even using the master branch of protobuf
> due to undefined references to some NoBarrier_Atomic*() functions.
> 
> Signed-off-by: Henrique Marks <henrique.marks@datacom.ind.br>
> Signed-off-by: Carlos Santos <casantos@datacom.ind.br>

Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

 The comment in Config.in is perhaps a bit heavy, but it definitely doesn't hurt.

[snip]

-- 
Arnout Vandecappelle                          arnout at mind be
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