Commit 498faea1 authored by Thierry Reding's avatar Thierry Reding
Browse files

disk cache: Link with -latomic if necessary

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 atomic, 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 2ef7f238 ("configure: check if
-latomic is needed for __atomic_*").

For some background information on this, see:

	https://gcc.gnu.org/wiki/Atomic/GCCMM



Changes in v2:
- clarify meaning of lock-free in commit message
- fix build if -latomic is not necessary
Acked-by: default avatarMatt Turner <mattst88@gmail.com>
Reviewed-by: default avatarDylan Baker <dylan@pnwbakers.com>
Signed-off-by: default avatarThierry Reding <treding@nvidia.com>
parent c133a341
......@@ -790,9 +790,26 @@ else
endif
# Check for GCC style atomics
dep_atomic = declare_dependency()
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;
......
......@@ -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
)
......
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