[PATCH 1/2] arm: Implement memcpy ifunc selection in C

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

This patch refactor ARM memcpy ifunc selector to a C implementation.
No functional change is expected, including ifunc resolution rules.

To avoid build issues with mainline GCC which set no default gnu
indirect function support for ARM (--enable-gnu-indirect-function)
two fixes are added:

  1. The new macro arm_libc_ifunc_hidden_def is redefined using
     direct asm assembly directives instead of function attributes.
     This avoid the incompatbile types for a symbol and its alias.

  2. A new macro NO_MEM_INTERAL_SYM_HACKS is added on symbol-hacks
     and defined on arm ifunc objects.  It avoids the symbol
     definition loop because compiler might emit the hacks for first
     fix before the ifunc function definition itself.

Checked on armv7-linux-gnueabihf and with a build for arm-linux-gnueabi,
arm-linux-gnueabihf with and without multiarch support and with both
GCC 7.1 and GCC mainline.

	* sysdeps/arm/arm-ifunc.h: New file.
	* sysdeps/arm/armv7/multiarch/ifunc-memcpy.h: Likewise.
	* sysdeps/arm/armv7/multiarch/memcpy.c: Likewise.
	* sysdeps/arm/armv7/multiarch/memcpy_arm.S: Likewise.
	* sysdeps/arm/armv7/multiarch/rtld-memcpy.S: Likewise.
	* sysdeps/arm/armv7/multiarch/Makefile [$(subdir) = string]
	(sysdep_routines): Add memcpy_arm.
	(CFLAGS-.os): New rule.
	* sysdeps/arm/armv7/multiarch/memcpy.S: Remove file.
	* sysdeps/generic/symbol-hacks.h: Use mem* alias hacks if not
	defined NO_MEM_INTERAL_SYM_HACKS.
---
 ChangeLog                                  | 12 +++++
 sysdeps/arm/arm-ifunc.h                    | 47 ++++++++++++++++++
 sysdeps/arm/armv7/multiarch/Makefile       |  8 +++-
 sysdeps/arm/armv7/multiarch/ifunc-memcpy.h | 37 +++++++++++++++
 sysdeps/arm/armv7/multiarch/memcpy.S       | 76 ------------------------------
 sysdeps/arm/armv7/multiarch/memcpy.c       | 33 +++++++++++++
 sysdeps/arm/armv7/multiarch/memcpy_arm.S   |  6 +++
 sysdeps/arm/armv7/multiarch/rtld-memcpy.S  |  1 +
 sysdeps/generic/symbol-hacks.h             |  3 +-
 9 files changed, 145 insertions(+), 78 deletions(-)
 create mode 100644 sysdeps/arm/arm-ifunc.h
 create mode 100644 sysdeps/arm/armv7/multiarch/ifunc-memcpy.h
 delete mode 100644 sysdeps/arm/armv7/multiarch/memcpy.S
 create mode 100644 sysdeps/arm/armv7/multiarch/memcpy.c
 create mode 100644 sysdeps/arm/armv7/multiarch/memcpy_arm.S
 create mode 100644 sysdeps/arm/armv7/multiarch/rtld-memcpy.S

diff --git a/sysdeps/arm/arm-ifunc.h b/sysdeps/arm/arm-ifunc.h
new file mode 100644
index 0000000..f7d3473
--- /dev/null
+++ b/sysdeps/arm/arm-ifunc.h
@@ -0,0 +1,47 @@
+/* Common definition for ifunc resolvers.  Linux/ARM version.
+   This file is part of the GNU C Library.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <sysdep.h>
+#include <ifunc-init.h>
+
+#define INIT_ARCH()
+
+#define arm_libc_ifunc_redirected(redirected_name, name, expr)	\
+  __ifunc (redirected_name, name, expr(hwcap), int hwcap, INIT_ARCH)
+
+#if defined SHARED
+# ifdef HAVE_GCC_IFUNC
+#  define arm_libc_ifunc_hidden_def(redirect_name, name) \
+  __hidden_ver1 (name, __GI_##name, redirect_name) \
+    __attribute__ ((visibility ("hidden")))
+# else
+/* GCC 8 without support for ifunc issues an error when trying to
+   alias symbols with different prototypes (in this case the redirect
+   one which have the same as the function implementation and the
+   ifunc resolver).  The macro below avoid it by issuing the required
+   alias directly.  */
+#  define arm_libc_ifunc_hidden_def(redirect_name, name) \
+  _arm_ifunc_hidden_ver (__GI_##name, name)
+#  define _arm_ifunc_hidden_ver(local, name)	\
+  asm (".globl " #local ";"			\
+       ".hidden " #local ";"			\
+       #local "=" #name)
+# endif
+#else
+# define arm_libc_ifunc_hidden_def(redirect_name, name)
+#endif
diff --git a/sysdeps/arm/armv7/multiarch/Makefile b/sysdeps/arm/armv7/multiarch/Makefile
index 9e1e61c..24c5e5a 100644
--- a/sysdeps/arm/armv7/multiarch/Makefile
+++ b/sysdeps/arm/armv7/multiarch/Makefile
@@ -1,3 +1,9 @@
 ifeq ($(subdir),string)
-sysdep_routines += memcpy_neon memcpy_vfp memchr_neon
+sysdep_routines += memcpy_neon memcpy_vfp memchr_neon memcpy_arm
+
+# For ifunc resolvers compiler might place the alias from generic
+# symbol-hacks.h before the resolver implementation itself.  This
+# causes definition loops and the macro below suppress the alias
+# definition.
+CFLAGS-.os += -DNO_MEM_INTERAL_SYM_HACKS
 endif
diff --git a/sysdeps/arm/armv7/multiarch/ifunc-memcpy.h b/sysdeps/arm/armv7/multiarch/ifunc-memcpy.h
new file mode 100644
index 0000000..78cef2a
--- /dev/null
+++ b/sysdeps/arm/armv7/multiarch/ifunc-memcpy.h
@@ -0,0 +1,37 @@
+/* Common definition for memcpy resolver.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifdef __SOFTFP__
+__typeof (REDIRECT_NAME) OPTIMIZE (arm) attribute_hidden;
+#endif
+__typeof (REDIRECT_NAME) OPTIMIZE (vfp) attribute_hidden;
+__typeof (REDIRECT_NAME) OPTIMIZE (neon) attribute_hidden;
+
+static inline void *
+IFUNC_SELECTOR (int hwcap)
+{
+  if (hwcap & HWCAP_ARM_NEON)
+    return OPTIMIZE (neon);
+#ifdef __SOFTFP__
+  if (hwcap & HWCAP_ARM_VFP)
+    return OPTIMIZE (vfp);
+  return OPTIMIZE (arm);
+#else
+  return OPTIMIZE (vfp);
+#endif
+}
diff --git a/sysdeps/arm/armv7/multiarch/memcpy.S b/sysdeps/arm/armv7/multiarch/memcpy.S
deleted file mode 100644
index 8a53bda..0000000
--- a/sysdeps/arm/armv7/multiarch/memcpy.S
+++ /dev/null
@@ -1,76 +0,0 @@
-/* Multiple versions of memcpy
-   All versions must be listed in ifunc-impl-list.c.
-   Copyright (C) 2013-2017 Free Software Foundation, Inc.
-   This file is part of the GNU C Library.
-
-   The GNU C Library is free software; you can redistribute it and/or
-   modify it under the terms of the GNU Lesser General Public
-   License as published by the Free Software Foundation; either
-   version 2.1 of the License, or (at your option) any later version.
-
-   The GNU C Library 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
-   Lesser General Public License for more details.
-
-   You should have received a copy of the GNU Lesser General Public
-   License along with the GNU C Library; if not, see
-   <http://www.gnu.org/licenses/>.  */
-
-/* Thumb requires excess IT instructions here.  */
-#define NO_THUMB
-#include <sysdep.h>
-#include <rtld-global-offsets.h>
-
-#if IS_IN (libc)
-/* Under __ARM_NEON__, memcpy_neon.S defines the name memcpy.  */
-# ifndef __ARM_NEON__
-	.text
-ENTRY(memcpy)
-	.type	memcpy, %gnu_indirect_function
-# ifdef __SOFTFP__
-	ldr	r1, .Lmemcpy_arm
-	tst	r0, #HWCAP_ARM_VFP
-	ldrne	r1, .Lmemcpy_vfp
-# else
-	ldr	r1, .Lmemcpy_vfp
-# endif
-	tst	r0, #HWCAP_ARM_NEON
-	ldrne	r1, .Lmemcpy_neon
-1:
-	add	r0, r1, pc
-	DO_RET(lr)
-
-# ifdef __SOFTFP__
-.Lmemcpy_arm:
-	.long	C_SYMBOL_NAME(__memcpy_arm) - 1b - PC_OFS
-# endif
-.Lmemcpy_neon:
-	.long	C_SYMBOL_NAME(__memcpy_neon) - 1b - PC_OFS
-.Lmemcpy_vfp:
-	.long	C_SYMBOL_NAME(__memcpy_vfp) - 1b - PC_OFS
-
-END(memcpy)
-
-libc_hidden_builtin_def (memcpy)
-#endif  /* Not __ARM_NEON__.  */
-
-/* These versions of memcpy are defined not to clobber any VFP or NEON
-   registers so they must always call the ARM variant of the memcpy code.  */
-strong_alias (__memcpy_arm, __aeabi_memcpy)
-strong_alias (__memcpy_arm, __aeabi_memcpy4)
-strong_alias (__memcpy_arm, __aeabi_memcpy8)
-libc_hidden_def (__memcpy_arm)
-
-#undef libc_hidden_builtin_def
-#define libc_hidden_builtin_def(name)
-#undef weak_alias
-#define weak_alias(x, y)
-#undef libc_hidden_def
-#define libc_hidden_def(name)
-
-#define memcpy __memcpy_arm
-
-#endif
-
-#include "memcpy_impl.S"
diff --git a/sysdeps/arm/armv7/multiarch/memcpy.c b/sysdeps/arm/armv7/multiarch/memcpy.c
new file mode 100644
index 0000000..7ef6714
--- /dev/null
+++ b/sysdeps/arm/armv7/multiarch/memcpy.c
@@ -0,0 +1,33 @@
+/* Multiple versions of memcpy.
+   All versions must be listed in ifunc-impl-list.c.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#if IS_IN (libc)
+# define memcpy __redirect_memcpy
+# include <string.h>
+# undef memcpy
+
+# include <arm-ifunc.h>
+
+# define SYMBOL_NAME memcpy
+# include "ifunc-memcpy.h"
+
+arm_libc_ifunc_redirected (__redirect_memcpy, memcpy, IFUNC_SELECTOR);
+
+arm_libc_ifunc_hidden_def (__redirect_memcpy, memcpy);
+#endif
diff --git a/sysdeps/arm/armv7/multiarch/memcpy_arm.S b/sysdeps/arm/armv7/multiarch/memcpy_arm.S
new file mode 100644
index 0000000..37565cd
--- /dev/null
+++ b/sysdeps/arm/armv7/multiarch/memcpy_arm.S
@@ -0,0 +1,6 @@
+#define memcpy __memcpy_arm
+#include "memcpy_impl.S"
+
+strong_alias (__memcpy_arm, __aeabi_memcpy)
+strong_alias (__memcpy_arm, __aeabi_memcpy4)
+strong_alias (__memcpy_arm, __aeabi_memcpy8)
diff --git a/sysdeps/arm/armv7/multiarch/rtld-memcpy.S b/sysdeps/arm/armv7/multiarch/rtld-memcpy.S
new file mode 100644
index 0000000..0190edc
--- /dev/null
+++ b/sysdeps/arm/armv7/multiarch/rtld-memcpy.S
@@ -0,0 +1 @@
+#include <./sysdeps/arm/armv7/multiarch/memcpy_impl.S>
diff --git a/sysdeps/generic/symbol-hacks.h b/sysdeps/generic/symbol-hacks.h
index d614c09..589585a 100644
--- a/sysdeps/generic/symbol-hacks.h
+++ b/sysdeps/generic/symbol-hacks.h
@@ -1,6 +1,7 @@
 /* Some compiler optimizations may transform loops into memset/memmove
    calls and without proper declaration it may generate PLT calls.  */
-#if !defined __ASSEMBLER__ && IS_IN (libc) && defined SHARED
+#if !defined __ASSEMBLER__ && IS_IN (libc) && defined SHARED \
+    && !defined(NO_MEM_INTERAL_SYM_HACKS)
 asm ("memmove = __GI_memmove");
 asm ("memset = __GI_memset");
 asm ("memcpy = __GI_memcpy");
-- 
2.7.4