+++ /dev/null
-From 5865c7cb4e4ed1d63699e384ea52984448adfec9 Mon Sep 17 00:00:00 2001
-From: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
-Date: Mon, 7 May 2018 10:36:10 +0200
-Subject: [PATCH] configure.ac: rework -latomic check
-
-The configure.ac logic added in commit
-2ef7f23820a67e958c2252bd81eb0458903ebf33 ("configure: check if
--latomic is needed for __atomic_*") makes the assumption that if a
-64-bit atomic intrinsic test program fails to link without -latomic,
-it is because we must use -latomic.
-
-Unfortunately, this is not completely correct: libatomic only appeared
-in gcc 4.8, and therefore gcc versions before that will not have
-libatomic, and therefore don't provide atomic intrinsics for all
-architectures. This issue was for example encountered on PowerPC with
-a gcc 4.7 toolchain, where the build fails with:
-
-powerpc-ctng_e500v2-linux-gnuspe/bin/ld: cannot find -latomic
-
-This commit aims at fixing that, by not assuming -latomic is
-available. The commit re-organizes the atomic intrinsics detection as
-follows:
-
- (1) Test if a program using 64-bit atomic intrinsics links properly,
- without -latomic. If this is the case, we have atomic intrinsics,
- and we're good to go.
-
- (2) If (1) has failed, then test to link the same program, but this
- time with -latomic in LDFLAGS. If this is the case, then we have
- atomic intrinsics, provided we link with -latomic.
-
-This has been tested in three situations:
-
- - On x86-64, where atomic instrinsics are all built-in, with no need
- for libatomic. In this case, config.log contains:
-
- GCC_ATOMIC_BUILTINS_SUPPORTED_FALSE='#'
- GCC_ATOMIC_BUILTINS_SUPPORTED_TRUE=''
- LIBATOMIC_LIBS=''
-
- This means: atomic intrinsics are available, and we don't need to
- link with libatomic.
-
- - On NIOS2, where atomic intrinsics are available, but some of them
- (64-bit ones) require using libatomic. In this case, config.log
- contains:
-
- GCC_ATOMIC_BUILTINS_SUPPORTED_FALSE='#'
- GCC_ATOMIC_BUILTINS_SUPPORTED_TRUE=''
- LIBATOMIC_LIBS='-latomic'
-
- This means: atomic intrinsics are available, and we need to link
- with libatomic.
-
- - On PowerPC with an old gcc 4.7 toolchain, where 32-bit atomic
- instrinsics are available, but not 64-bit atomic instrinsics, and
- there is no libatomic. In this case, config.log contains:
-
- GCC_ATOMIC_BUILTINS_SUPPORTED_FALSE=''
- GCC_ATOMIC_BUILTINS_SUPPORTED_TRUE='#'
-
- With means that atomic intrinsics are not usable.
-
-Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
-Upstream-status: https://lists.freedesktop.org/archives/mesa-dev/2018-May/194214.html
----
- configure.ac | 37 +++++++++++++++++++++----------------
- 1 file changed, 21 insertions(+), 16 deletions(-)
-
-diff --git a/configure.ac b/configure.ac
-index f1fbdcc6c7..c94e547874 100644
---- a/configure.ac
-+++ b/configure.ac
-@@ -433,26 +433,31 @@ fi
- AM_CONDITIONAL([SSE41_SUPPORTED], [test x$SSE41_SUPPORTED = x1])
- AC_SUBST([SSE41_CFLAGS], $SSE41_CFLAGS)
-
--dnl Check for new-style atomic builtins
--AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
-+dnl Check for new-style atomic builtins. We first check without linking to
-+dnl -latomic.
-+AC_LINK_IFELSE([AC_LANG_SOURCE([[
-+#include <stdint.h>
- int main() {
-- int n;
-- return __atomic_load_n(&n, __ATOMIC_ACQUIRE);
-+ uint64_t n;
-+ return (int)__atomic_load_n(&n, __ATOMIC_ACQUIRE);
- }]])], GCC_ATOMIC_BUILTINS_SUPPORTED=1)
-+
-+dnl If that didn't work, we try linking with -latomic, which is needed on some
-+dnl platforms.
-+if test "x$GCC_ATOMIC_BUILTINS_SUPPORTED" != x1; then
-+ save_LDFLAGS=$LDFLAGS
-+ LDFLAGS="$LDFLAGS -latomic"
-+ AC_LINK_IFELSE([AC_LANG_SOURCE([[
-+ #include <stdint.h>
-+ int main() {
-+ uint64_t n;
-+ return (int)__atomic_load_n(&n, __ATOMIC_ACQUIRE);
-+ }]])], GCC_ATOMIC_BUILTINS_SUPPORTED=1 LIBATOMIC_LIBS="-latomic")
-+ LDFLAGS=$save_LDFLAGS
-+fi
-+
- if test "x$GCC_ATOMIC_BUILTINS_SUPPORTED" = x1; then
- DEFINES="$DEFINES -DUSE_GCC_ATOMIC_BUILTINS"
-- dnl On some platforms, new-style atomics need a helper library
-- AC_MSG_CHECKING(whether -latomic is needed)
-- AC_LINK_IFELSE([AC_LANG_SOURCE([[
-- #include <stdint.h>
-- uint64_t v;
-- int main() {
-- return (int)__atomic_load_n(&v, __ATOMIC_ACQUIRE);
-- }]])], GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC=no, GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC=yes)
-- AC_MSG_RESULT($GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC)
-- if test "x$GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC" = xyes; then
-- LIBATOMIC_LIBS="-latomic"
-- fi
- fi
- AC_SUBST([LIBATOMIC_LIBS])
-
---
-2.14.3
-
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