From 498faea103aa7966b435f21d8ff5e36172389b1e Mon Sep 17 00:00:00 2001 From: Thierry Reding Date: Fri, 23 Feb 2018 14:13:27 +0100 Subject: [PATCH] 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 2ef7f23820a6 ("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: Matt Turner Reviewed-by: Dylan Baker Signed-off-by: Thierry Reding --- meson.build | 17 +++++++++++++++++ src/util/meson.build | 2 +- 2 files changed, 18 insertions(+), 1 deletion(-) diff --git a/meson.build b/meson.build index e9928a37931..bb6a835084f 100644 --- a/meson.build +++ b/meson.build @@ -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 + 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 uint64_t v; diff --git a/src/util/meson.build b/src/util/meson.build index b23dba3a985..eece1cefef6 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 ) -- 2.30.2