Re: [Buildroot] [PATCH 1/2] package/libgit2: depends on native 64bit atomics

[Thomas Petazzoni via buildroot <buildroot@buildroot.org>]

Hello Nicolas,

On Mon,  8 Aug 2022 17:06:40 +0200
Nicolas Cavallari <nicolas.cavallari@green-communications.fr> wrote:

> libgit2 does not know about libatomic_ops.
> 
> This wasn't a problem before because it is a shared library, so the
> missing symbols were simply added as undefined, and no project currently
> depend on libgit2 to expose the problem.
> 
> The next version of libgit2 can also build a binary, which will expose
> the problem.
> 
> Signed-off-by: Nicolas Cavallari <nicolas.cavallari@green-communications.fr>

Which build failure do you have exactly? Indeed when building for
SPARC, what I see are calls to __atomic_compare_exchange_4,
__atomic_fetch_add_4, __atomic_fetch_sub_4.

Is this what you are referring to?

If yes, then these are not sync builtins
(https://gcc.gnu.org/onlinedocs/gcc/_005f_005fsync-Builtins.html), but
atomic builtins
(https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html).

The Buildroot options BR2_TOOLCHAIN_HAS_SYNC_xyz are for sync builtins.

The Buildroot option BR2_TOOLCHAIN_HAS_ATOMIC is for atomic builtins.

So, your package needs to:

	depends on BR2_TOOLCHAIN_HAS_ATOMIC

and then in its .mk file, so something like this:

ifeq ($(BR2_TOOLCHAIN_HAS_LIBATOMIC),y)
... make sure your package links against libatomic.so by passing -latomic in LDFLAGS
endif

Note that libatomic.so is distinct from libatomic_ops.so. libatomic.so
is provided together with the gcc runtime, and implements the atomic
builtins on architecture where they are not implemented directly by the
compiler (a runtime library is needed).

Best regards,

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com
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