Re: [Patch][aarch64] Use IFUNCs to enable LSE instructions in libatomic on aarch64

[Steve Ellcey <sellcey@cavium.com>]

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On Thu, 2017-09-28 at 12:31 +0100, Szabolcs Nagy wrote:
> 
> i think this should be improved, see below.

Those were all good suggestions, here is a new patch that incorporates
the changes.  I fixed the IFUNC_OPTIONS argument,
renamed ARCH_AARCH64_LINUX_LSE, got rid of the auxv references, and
changed HWCAP_TYPE to IFUNC_RESOLVER_ARGS.

Here is the new patch, tested with no regressions.

Steve Ellcey
sellcey@cavium.com


2017-09-29  Steve Ellcey  <sellcey@cavium.com>

	* Makefile.am (ARCH_AARCH64_LINUX): Add IFUNC_OPTIONS and
	libatomic_la_LIBADD.
	* config/linux/aarch64/host-config.h: New file.
	* configure.ac (IFUNC_RESOLVER_ARGS): Define.
	(ARCH_AARCH64_LINUX): New conditional for IFUNC builds.
	* configure.tgt (aarch64): Set ARCH and try_ifunc.
	(aarch64*-*-linux*) Update config_path.
	(aarch64*-*-linux*) Set IFUNC_RESOLVER_ARGS.
	* libatomic_i.h (GEN_SELECTOR): Add IFUNC_RESOLVER_ARGS argument.
	* Makefile.in: Regenerate.
	* auto-config.h.in: Regenerate.
	* configure: Regenerate.


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diff --git a/libatomic/Makefile.am b/libatomic/Makefile.am
index d731406..92d19c6 100644
--- a/libatomic/Makefile.am
+++ b/libatomic/Makefile.am
@@ -122,6 +122,10 @@ libatomic_la_LIBADD = $(foreach s,$(SIZES),$(addsuffix _$(s)_.lo,$(SIZEOBJS)))
 
 ## On a target-specific basis, include alternates to be selected by IFUNC.
 if HAVE_IFUNC
+if ARCH_AARCH64_LINUX
+IFUNC_OPTIONS	     = -march=armv8.1-a
+libatomic_la_LIBADD += $(foreach s,$(SIZES),$(addsuffix _$(s)_1_.lo,$(SIZEOBJS)))
+endif
 if ARCH_ARM_LINUX
 IFUNC_OPTIONS	     = -march=armv7-a -DHAVE_KERNEL64
 libatomic_la_LIBADD += $(foreach s,$(SIZES),$(addsuffix _$(s)_1_.lo,$(SIZEOBJS)))
diff --git a/libatomic/config/linux/aarch64/host-config.h b/libatomic/config/linux/aarch64/host-config.h
index e69de29..08810a9 100644
--- a/libatomic/config/linux/aarch64/host-config.h
+++ b/libatomic/config/linux/aarch64/host-config.h
@@ -0,0 +1,36 @@
+/* Copyright (C) 2017 Free Software Foundation, Inc.
+
+   This file is part of the GNU Atomic Library (libatomic).
+
+   Libatomic is free software; you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   Libatomic is distributed in the hope that it will be useful, but WITHOUT ANY
+   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+   FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+   more details.
+
+   Under Section 7 of GPL version 3, you are granted additional
+   permissions described in the GCC Runtime Library Exception, version
+   3.1, as published by the Free Software Foundation.
+
+   You should have received a copy of the GNU General Public License and
+   a copy of the GCC Runtime Library Exception along with this program;
+   see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#if HAVE_IFUNC
+#include <stdlib.h>
+
+# ifdef HWCAP_ATOMICS
+#  define IFUNC_COND_1	(hwcap & HWCAP_ATOMICS)
+# else
+#  define IFUNC_COND_1	(false)
+# endif
+# define IFUNC_NCOND(N)	(1)
+
+#endif /* HAVE_IFUNC */
+
+#include_next <host-config.h>
diff --git a/libatomic/configure.ac b/libatomic/configure.ac
index 023f172..b717d3d 100644
--- a/libatomic/configure.ac
+++ b/libatomic/configure.ac
@@ -163,6 +163,10 @@ if test -n "$UNSUPPORTED"; then
   AC_MSG_ERROR([Configuration ${target} is unsupported.])
 fi
 
+# Write out the ifunc resolver arg type.
+AC_DEFINE_UNQUOTED(IFUNC_RESOLVER_ARGS, $IFUNC_RESOLVER_ARGS,
+	[Define ifunc resolver function argument.])
+
 # Disable fallbacks to __sync routines from libgcc.  Otherwise we'll
 # make silly decisions about what the cpu can do.
 CFLAGS="$save_CFLAGS -fno-sync-libcalls $XCFLAGS"
@@ -247,6 +251,8 @@ AC_SUBST(LIBS)
 AC_SUBST(SIZES)
 
 AM_CONDITIONAL(HAVE_IFUNC, test x$libat_cv_have_ifunc = xyes)
+AM_CONDITIONAL(ARCH_AARCH64_LINUX,
+	       [expr "$config_path" : ".* linux/aarch64 .*" > /dev/null])
 AM_CONDITIONAL(ARCH_ARM_LINUX,
 	       [expr "$config_path" : ".* linux/arm .*" > /dev/null])
 AM_CONDITIONAL(ARCH_I386,
diff --git a/libatomic/configure.tgt b/libatomic/configure.tgt
index b8af3ab..388ae95 100644
--- a/libatomic/configure.tgt
+++ b/libatomic/configure.tgt
@@ -40,6 +40,14 @@ case "${target_cpu}" in
   riscv*)		ARCH=riscv ;;
   sh*)			ARCH=sh ;;
 
+  aarch64*)
+	ARCH=aarch64
+	case "${target}" in
+	    aarch64*-*-linux*)
+		try_ifunc=yes
+		;;
+	esac
+	;;
   arm*)
 	ARCH=arm
 	case "${target}" in
@@ -109,6 +117,11 @@ fi
 
 # Other system configury
 case "${target}" in
+  aarch64*-*-linux*)
+	# OS support for atomic primitives.
+	config_path="${config_path} linux/aarch64 posix"
+	;;
+
   arm*-*-linux*)
 	# OS support for atomic primitives.
 	config_path="${config_path} linux/arm posix"
@@ -153,3 +166,14 @@ case "${target}" in
 	UNSUPPORTED=1
 	;;
 esac
+
+# glibc will pass hwcap to ifunc resolver functions as an argument.
+# The type may be different on different architectures.
+case "${target}" in
+  aarch64*-*-*)
+	IFUNC_RESOLVER_ARGS="uint64_t hwcap"
+	;;
+  *)
+	IFUNC_RESOLVER_ARGS="void"
+	;;
+esac
diff --git a/libatomic/libatomic_i.h b/libatomic/libatomic_i.h
index 4eb372a..b25f2f3 100644
--- a/libatomic/libatomic_i.h
+++ b/libatomic/libatomic_i.h
@@ -240,7 +240,7 @@ bool libat_is_lock_free (size_t, void *) MAN(is_lock_free);
 # if IFUNC_NCOND(N) == 1
 #  define GEN_SELECTOR(X)					\
 	extern typeof(C2(libat_,X)) C3(libat_,X,_i1) HIDDEN;	\
-	static void * C2(select_,X) (void)			\
+	static void * C2(select_,X) (IFUNC_RESOLVER_ARGS)	\
 	{							\
 	  if (IFUNC_COND_1)					\
 	    return C3(libat_,X,_i1);				\
@@ -250,7 +250,7 @@ bool libat_is_lock_free (size_t, void *) MAN(is_lock_free);
 #  define GEN_SELECTOR(X)					\
 	extern typeof(C2(libat_,X)) C3(libat_,X,_i1) HIDDEN;	\
 	extern typeof(C2(libat_,X)) C3(libat_,X,_i2) HIDDEN;	\
-	static void * C2(select_,X) (void)			\
+	static void * C2(select_,X) (IFUNC_RESOLVER_ARGS)	\
 	{							\
 	  if (IFUNC_COND_1)					\
 	    return C3(libat_,X,_i1);				\
@@ -263,7 +263,7 @@ bool libat_is_lock_free (size_t, void *) MAN(is_lock_free);
 	extern typeof(C2(libat_,X)) C3(libat_,X,_i1) HIDDEN;	\
 	extern typeof(C2(libat_,X)) C3(libat_,X,_i2) HIDDEN;	\
 	extern typeof(C2(libat_,X)) C3(libat_,X,_i3) HIDDEN;	\
-	static void * C2(select_,X) (void)			\
+	static void * C2(select_,X) (IFUNC_RESOLVER_ARGS)	\
 	{							\
 	  if (IFUNC_COND_1)					\
 	    return C3(libat_,X,_i1);				\