From 54bbe600ec2654bcf43c3378e84d972e0a7ce4b6 Mon Sep 17 00:00:00 2001 From: Thomas Petazzoni Date: Mon, 7 May 2018 13:34:11 +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. Reviewed-by: Matt Turner Signed-off-by: Thomas Petazzoni --- configure.ac | 44 +++++++++++++++++++++++++++----------------- 1 file changed, 27 insertions(+), 17 deletions(-) diff --git a/configure.ac b/configure.ac index 4bb8960..35ade98 100644 --- a/configure.ac +++ b/configure.ac @@ -434,28 +434,38 @@ fi AM_CONDITIONAL([SSE41_SUPPORTED], [test x$SSE41_SUPPORTED = x1]) AC_SUBST([SSE41_CFLAGS], $SSE41_CFLAGS) -dnl Check for new-style atomic builtins -AC_COMPILE_IFELSE([AC_LANG_SOURCE([[ +dnl Check for new-style atomic builtins. We first check without linking to +dnl -latomic. +AC_MSG_CHECKING(whether __atomic_load_n is supported) +AC_LINK_IFELSE([AC_LANG_SOURCE([[ +#include int main() { - int n; - return __atomic_load_n(&n, __ATOMIC_ACQUIRE); -}]])], GCC_ATOMIC_BUILTINS_SUPPORTED=1) -if test "x$GCC_ATOMIC_BUILTINS_SUPPORTED" = x1; then - DEFINES="$DEFINES -DUSE_GCC_ATOMIC_BUILTINS" - dnl On some platforms, new-style atomics need a helper library - AC_MSG_CHECKING(whether -latomic is needed) - AC_LINK_IFELSE([AC_LANG_SOURCE([[ - #include struct { uint64_t *v; } x; - int main() { + return (int)__atomic_load_n(x.v, __ATOMIC_ACQUIRE); +}]])], GCC_ATOMIC_BUILTINS_SUPPORTED=yes, GCC_ATOMIC_BUILTINS_SUPPORTED=no) + +dnl If that didn't work, we try linking with -latomic, which is needed on some +dnl platforms. +if test "x$GCC_ATOMIC_BUILTINS_SUPPORTED" != xyes; then + save_LDFLAGS=$LDFLAGS + LDFLAGS="$LDFLAGS -latomic" + AC_LINK_IFELSE([AC_LANG_SOURCE([[ + #include + 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=$save_LDFLAGS +fi +AC_MSG_RESULT($GCC_ATOMIC_BUILTINS_SUPPORTED) + +if test "x$GCC_ATOMIC_BUILTINS_SUPPORTED" = xyes; then + DEFINES="$DEFINES -DUSE_GCC_ATOMIC_BUILTINS" fi AC_SUBST([LIBATOMIC_LIBS]) -- 2.7.4