libspl: implement atomics in terms of atomics

cmd/zed/Makefile.am

@@ -43,7 +43,7 @@ zed_LDADD = \
 	$(abs_top_builddir)/lib/libnvpair/libnvpair.la \
 	$(abs_top_builddir)/lib/libuutil/libuutil.la
 
-zed_LDADD += -lrt $(LIBUDEV_LIBS) $(LIBUUID_LIBS)
+zed_LDADD += -lrt $(LIBATOMIC_LIBS) $(LIBUDEV_LIBS) $(LIBUUID_LIBS)
 zed_LDFLAGS = -pthread
 
 EXTRA_DIST = agents/README.md

config/user-libatomic.m4

@@ -0,0 +1,34 @@
+dnl #
+dnl # If -latomic exists, it's needed for __atomic intrinsics.
+dnl #
+dnl # Some systems (like FreeBSD 13) don't have a libatomic at all because
+dnl # their toolchain doesn't ship it – they obviously don't need it.
+dnl #
+dnl # Others (like sufficiently ancient CentOS) have one,
+dnl # but terminally broken or unlinkable (e.g. it's a dangling symlink,
+dnl # or a linker script that points to a nonexistent file) –
+dnl # most arches affected by this don't actually need -latomic (and if they do,
+dnl # then they should have libatomic that actually exists and links,
+dnl # so don't fall into this category).
+dnl #
+dnl # Technically, we could check if the platform *actually* needs -latomic,
+dnl # or if it has native support for all the intrinsics we use,
+dnl # but it /really/ doesn't matter, and C11 recommends to always link it.
+dnl #
+AC_DEFUN([ZFS_AC_CONFIG_USER_LIBATOMIC], [
+	AC_MSG_CHECKING([whether -latomic is present])
+
+	saved_libs="$LIBS"
+	LIBS="$LIBS -latomic"
+
+	AC_LINK_IFELSE([AC_LANG_PROGRAM([], [])], [
+		LIBATOMIC_LIBS="-latomic"
+		AC_MSG_RESULT([yes])
+	], [
+		LIBATOMIC_LIBS=""
+		AC_MSG_RESULT([no])
+	])
+
+	LIBS="$saved_libs"
+	AC_SUBST([LIBATOMIC_LIBS])
+])

config/user.m4

@@ -21,6 +21,7 @@ AC_DEFUN([ZFS_AC_CONFIG_USER], [
 	ZFS_AC_CONFIG_USER_LIBUDEV
 	ZFS_AC_CONFIG_USER_LIBCRYPTO
 	ZFS_AC_CONFIG_USER_LIBAIO
+	ZFS_AC_CONFIG_USER_LIBATOMIC
 	ZFS_AC_CONFIG_USER_CLOCK_GETTIME
 	ZFS_AC_CONFIG_USER_PAM
 	ZFS_AC_CONFIG_USER_RUNSTATEDIR

lib/libspl/Makefile.am

@@ -1,27 +1,15 @@
 include $(top_srcdir)/config/Rules.am
 
-if TARGET_CPU_I386
-TARGET_CPU_ATOMIC_SOURCE = asm-i386/atomic.S
-else
-if TARGET_CPU_X86_64
-TARGET_CPU_ATOMIC_SOURCE = asm-x86_64/atomic.S
-else
-TARGET_CPU_ATOMIC_SOURCE = asm-generic/atomic.c
-endif
-endif
-
 SUBDIRS = include
 
-AM_CCASFLAGS = \
-	$(CFLAGS)
-
 noinst_LTLIBRARIES = libspl_assert.la libspl.la
 
 libspl_assert_la_SOURCES = \
 	assert.c
 
 USER_C = \
 	libspl_impl.h \
+	atomic.c \
 	getexecname.c \
 	list.c \
 	mkdirp.c \
@@ -49,20 +37,11 @@ USER_C += \
 	os/freebsd/zone.c
 endif
 
-libspl_la_SOURCES = \
-	$(USER_C) \
-	$(TARGET_CPU_ATOMIC_SOURCE)
+libspl_la_SOURCES = $(USER_C)
 
 libspl_la_LIBADD = \
 	libspl_assert.la
 
-libspl_la_LIBADD += $(LIBCLOCK_GETTIME)
+libspl_la_LIBADD += $(LIBATOMIC_LIBS) $(LIBCLOCK_GETTIME)
 
 include $(top_srcdir)/config/CppCheck.am
-
-# Override the default SOURCES which includes TARGET_CPU_ATOMIC_SOURCE
-# in order to always evaluate the generic asm-generic/atomic.c source.
-CPPCHECKSRC = $(USER_C) asm-generic/atomic.c
-cppcheck:
-	$(CPPCHECK) -j$(CPU_COUNT) $(CPPCHECKFLAGS) --force \
-		$(DEFAULT_INCLUDES) $(CPPCHECKSRC)