[Mesa-dev] [PATCH] configure.ac: rework -latomic check

[Thomas Petazzoni]

Hello Matt,

On Wed,  9 May 2018 16:30:12 -0700, Matt Turner wrote:

> Hi Thomas,
> 
> I rebased this patch on
> 
> 	commit 54ba73ef102f7b9085922686bb31719539e0dc3c
> 	Author: Nicolas Boichat <drinkcat at chromium.org>
> 	Date:   Thu Apr 5 09:33:09 2018 +0800
> 
> 	    configure.ac/meson.build: Fix -latomic test
> 
> and readded the AC_MSG_CHECKING/AC_MSG_RESULT. If it looks good to you,
> I'll commit it.

Thanks for this new iteration! I didn't test it, but it looks good to
me. Just one minor nit below.

> -dnl Check for new-style atomic builtins
> -AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
> +dnl Check for new-style atomic builtins. We first check without linking to
> +dnl -latomic.
> +AC_MSG_CHECKING(whether __atomic_load_n is supported)
> +AC_LINK_IFELSE([AC_LANG_SOURCE([[
> +#include <stdint.h>
>  int main() {
> -    int n;
> -    return __atomic_load_n(&n, __ATOMIC_ACQUIRE);
> -}]])], GCC_ATOMIC_BUILTINS_SUPPORTED=1)
> -if test "x$GCC_ATOMIC_BUILTINS_SUPPORTED" = x1; then
> -    DEFINES="$DEFINES -DUSE_GCC_ATOMIC_BUILTINS"
> -    dnl On some platforms, new-style atomics need a helper library
> -    AC_MSG_CHECKING(whether -latomic is needed)
> -    AC_LINK_IFELSE([AC_LANG_SOURCE([[
> -    #include <stdint.h>
>      struct {
>          uint64_t *v;
>      } x;
> -    int main() {
> +    return (int)__atomic_load_n(x.v, __ATOMIC_ACQUIRE);
> +}]])], GCC_ATOMIC_BUILTINS_SUPPORTED=yes, GCC_ATOMIC_BUILTINS_SUPPORTED=no)
> +
> +dnl If that didn't work, we try linking with -latomic, which is needed on some
> +dnl platforms.
> +if test "x$GCC_ATOMIC_BUILTINS_SUPPORTED" != xyes; then
> +   save_LDFLAGS=$LDFLAGS
> +   LDFLAGS="$LDFLAGS -latomic"
> +   AC_LINK_IFELSE([AC_LANG_SOURCE([[
> +   #include <stdint.h>
> +   int main() {
> +        struct {
> +            uint64_t *v;
> +        } x;
>          return (int)__atomic_load_n(x.v, __ATOMIC_ACQUIRE);
> -    }]])], GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC=no, GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC=yes)
> -    AC_MSG_RESULT($GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC)
> -    if test "x$GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC" = xyes; then
> -        LIBATOMIC_LIBS="-latomic"
> -    fi
> +   }]])], GCC_ATOMIC_BUILTINS_SUPPORTED=yes LIBATOMIC_LIBS="-latomic",
> +          GCC_ATOMIC_BUILTINS_SUPPORTED=no)
> +   LDFLAGS=$save_LDFLAGS
> +
> +

Those two empty lines don't seem to be very useful.

> +fi
> +AC_MSG_RESULT($GCC_ATOMIC_BUILTINS_SUPPORTED)
> +
> +if test "x$GCC_ATOMIC_BUILTINS_SUPPORTED" = xyes; then
> +    DEFINES="$DEFINES -DUSE_GCC_ATOMIC_BUILTINS"
>  fi
>  AC_SUBST([LIBATOMIC_LIBS])
>  

Thanks!

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com