[Mesa-dev] [PATCH] configure.ac: Fix -latomic test

[Nicolas Boichat]

Scrap this, I guess I should update meson.build, too.

Will send v2 in a few minutes.

On Thu, Mar 29, 2018 at 4:26 PM, Nicolas Boichat <drinkcat at chromium.org> wrote:
> From: Nicolas Boichat <drinkcat at chromium.org>
>
> When compiling with LLVM 6.0, the test fails to detect that
> -latomic is actually required, as the atomic call is inlined.
>
> In the code itself (src/util/disk_cache.c), we see this pattern:
> p_atomic_add(cache->size, - (uint64_t)size);
> where cache->size is an uint64_t *, and results in the following
> link time error without -latomic:
> src/util/disk_cache.c:628: error: undefined reference to '__atomic_fetch_add_8'
>
> Fix the configure test to replicate this pattern, which then
> correctly realizes the need for -latomic.
>
> Signed-off-by: Nicolas Boichat <drinkcat at chromium.org>
> ---
>  configure.ac | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/configure.ac b/configure.ac
> index e874f8ebfb2..eff9a0ef88f 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -445,9 +445,11 @@ if test "x$GCC_ATOMIC_BUILTINS_SUPPORTED" = x1; then
>      AC_MSG_CHECKING(whether -latomic is needed)
>      AC_LINK_IFELSE([AC_LANG_SOURCE([[
>      #include <stdint.h>
> -    uint64_t v;
> +    struct {
> +        uint64_t* v;
> +    } x;
>      int main() {
> -        return (int)__atomic_load_n(&v, __ATOMIC_ACQUIRE);
> +        return (int)__atomic_load_n(x.v, __ATOMIC_ACQUIRE);
>      }]])], GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC=no, GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC=yes)
>      AC_MSG_RESULT($GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC)
>      if test "x$GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC" = xyes; then
> --
> 2.17.0.rc1.321.gba9d0f2565-goog
>