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

[Mike Lothian]

On Fri, 23 Feb 2018 at 13:18 Thierry Reding <thierry.reding at gmail.com>
wrote:

> 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')
> +  endif
>  endif
>  if not cc.links('''#include <stdint.h>
>                     uint64_t v;
> diff --git a/src/util/meson.build b/src/util/meson.build
> index b23dba3a9851..eece1cefef6a 100644
> --- a/src/util/meson.build
> +++ b/src/util/meson.build
> @@ -102,7 +102,7 @@ libmesa_util = static_library(
>    'mesa_util',
>    [files_mesa_util, format_srgb],
>    include_directories : inc_common,
> -  dependencies : [dep_zlib, dep_clock, dep_thread],
> +  dependencies : [dep_zlib, dep_clock, dep_thread, dep_atomic],
>    c_args : [c_msvc_compat_args, c_vis_args],
>    build_by_default : false
>  )
> --
> 2.16.2
>
>
Hi

I had this issue when building a 32bit Mesa on x86-64 when using Clang,
64bit was fine.

Will this work for Clang too and if so can a similar change be made for
autotools?

I'm waiting for a change to Meson that'll allow me to specify a 32bit
llvm-config to test this on Meson with 32bit

Thanks

Mike
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.freedesktop.org/archives/mesa-dev/attachments/20180226/51f56303/attachment.html>