[Mesa-dev] [PATCH] disk cache: Link with -latomic if necessary

[Dylan Baker]

Quoting Thierry Reding (2018-02-23 05:18:28)
> From: Thierry Reding <treding at nvidia.com>
> 
> The disk cache implementation uses 64-bit atomic operations. For some
> architectures, such as 32-bit ARM, GCC will not be able to translate
> these operations into lock-free instructions and will instead rely on
> the external atomics library to provide these operations.
> 
> Check at configuration time whether or not linking against libatomic
> is necessary and if so, create a dependency that can be used while
> linking the mesautil library.
> 
> This is the meson equivalent of 2ef7f23820a6 ("configure: check if
> -latomic is needed for __atomic_*").
> 
> Signed-off-by: Thierry Reding <treding at nvidia.com>
> ---
>  meson.build          | 15 +++++++++++++++
>  src/util/meson.build |  2 +-
>  2 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/meson.build b/meson.build
> index 121341a950c4..7c6f40573421 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -800,6 +800,21 @@ endif
>  if cc.compiles('int main() { int n; return __atomic_load_n(&n, __ATOMIC_ACQUIRE); }',
>                 name : 'GCC atomic builtins')
>    pre_args += '-DUSE_GCC_ATOMIC_BUILTINS'
> +
> +  # Not all atomic calls can be turned into lock-free instructions, in which
> +  # GCC will make calls into the libatomic library. Check whether we need to
> +  # link with -latomic.
> +  #
> +  # This can happen for 64-bit atomic operations on 32-bit architectures such
> +  # as ARM.
> +  if not cc.links('''#include <stdint.h>
> +                     int main() {
> +                       uint64_t n;
> +                       return (int)__atomic_load_n(&n, __ATOMIC_ACQUIRE);
> +                     }''',
> +                  name : 'GCC atomic builtins required -latomic')
> +    dep_atomic = cc.find_library('atomic')

dep_atomic is undefined if the cc.links() succeeds right?

Dylan
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