Patchwork x86-64: Implement memcmp family IFUNC selectors in C

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Submitter H.J. Lu
Date June 12, 2017, 4:10 p.m.
Message ID <20170612161027.GC25262@gmail.com>
Download mbox | patch
Permalink /patch/20951/
State New
Headers show

Comments

H.J. Lu - June 12, 2017, 4:10 p.m.
Implement memcmp family IFUNC selectors in C.

All internal calls within libc.so can use IFUNC on x86-64 since unlike
x86, x86-64 supports PC-relative addressing to access the GOT entry so
that it can call via PLT without using an extra register.  For libc.a,
we can't use IFUNC for functions which are called before IFUNC has been
initialized.  Use IFUNC internally reduces the icache footprint since
libc.so and other codes in the process use the same implementations.
This patch uses IFUNC for memcmp family functions within libc.

Any comments?

H.J.
---
2017-06-07  H.J. Lu  <hongjiu.lu@intel.com>
	    Erich Elsen  <eriche@google.com>

	* sysdeps/x86_64/multiarch/Makefile (sysdep_routines): Add
	memcmp-sse2.
	* sysdeps/x86_64/multiarch/ifunc-memcmp.h: New file.
	* sysdeps/x86_64/multiarch/memcmp-sse2.S: Likewise.
	* sysdeps/x86_64/multiarch/memcmp.c: Likewise.
	* sysdeps/x86_64/multiarch/wmemcmp.c: Likewise.
	* sysdeps/x86_64/multiarch/memcmp.S: Removed.
	* sysdeps/x86_64/multiarch/wmemcmp.S: Likewise.
---
 sysdeps/x86_64/multiarch/Makefile                  |  1 +
 sysdeps/x86_64/multiarch/ifunc-impl-list.c         |  4 +-
 sysdeps/x86_64/multiarch/ifunc-memcmp.h            | 45 +++++++++++++
 .../x86_64/multiarch/{wmemcmp.S => memcmp-sse2.S}  | 44 +++---------
 sysdeps/x86_64/multiarch/memcmp.S                  | 78 ----------------------
 sysdeps/x86_64/multiarch/memcmp.c                  | 38 +++++++++++
 sysdeps/x86_64/multiarch/wmemcmp.c                 | 31 +++++++++
 7 files changed, 128 insertions(+), 113 deletions(-)
 create mode 100644 sysdeps/x86_64/multiarch/ifunc-memcmp.h
 rename sysdeps/x86_64/multiarch/{wmemcmp.S => memcmp-sse2.S} (54%)
 delete mode 100644 sysdeps/x86_64/multiarch/memcmp.S
 create mode 100644 sysdeps/x86_64/multiarch/memcmp.c
 create mode 100644 sysdeps/x86_64/multiarch/wmemcmp.c
Adhemerval Zanella Netto - June 15, 2017, 3:29 p.m.
On 12/06/2017 13:10, H.J. Lu wrote:
> Implement memcmp family IFUNC selectors in C.
> 
> All internal calls within libc.so can use IFUNC on x86-64 since unlike
> x86, x86-64 supports PC-relative addressing to access the GOT entry so
> that it can call via PLT without using an extra register.  For libc.a,
> we can't use IFUNC for functions which are called before IFUNC has been
> initialized.  Use IFUNC internally reduces the icache footprint since
> libc.so and other codes in the process use the same implementations.
> This patch uses IFUNC for memcmp family functions within libc.
> 
> Any comments?
> 
> H.J.
> ---
> 2017-06-07  H.J. Lu  <hongjiu.lu@intel.com>
> 	    Erich Elsen  <eriche@google.com>
> 
> 	* sysdeps/x86_64/multiarch/Makefile (sysdep_routines): Add
> 	memcmp-sse2.
> 	* sysdeps/x86_64/multiarch/ifunc-memcmp.h: New file.
> 	* sysdeps/x86_64/multiarch/memcmp-sse2.S: Likewise.
> 	* sysdeps/x86_64/multiarch/memcmp.c: Likewise.
> 	* sysdeps/x86_64/multiarch/wmemcmp.c: Likewise.
> 	* sysdeps/x86_64/multiarch/memcmp.S: Removed.
> 	* sysdeps/x86_64/multiarch/wmemcmp.S: Likewise.

LGTM.

Patch

diff --git a/sysdeps/x86_64/multiarch/Makefile b/sysdeps/x86_64/multiarch/Makefile
index 810bd1f..7d7c142 100644
--- a/sysdeps/x86_64/multiarch/Makefile
+++ b/sysdeps/x86_64/multiarch/Makefile
@@ -8,6 +8,7 @@  sysdep_routines += strncat-c stpncpy-c strncpy-c strcmp-ssse3 \
 		   strcmp-sse2-unaligned strncmp-ssse3 \
 		   memchr-sse2 rawmemchr-sse2 memchr-avx2 rawmemchr-avx2 \
 		   memrchr-sse2 memrchr-avx2 \
+		   memcmp-sse2 \
 		   memcmp-avx2-movbe \
 		   memcmp-sse4 memcpy-ssse3 \
 		   memmove-ssse3 \
diff --git a/sysdeps/x86_64/multiarch/ifunc-impl-list.c b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
index 52ea440..7912dd0 100644
--- a/sysdeps/x86_64/multiarch/ifunc-impl-list.c
+++ b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
@@ -45,7 +45,7 @@  __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			      __memchr_avx2)
 	      IFUNC_IMPL_ADD (array, i, memchr, 1, __memchr_sse2))
 
-  /* Support sysdeps/x86_64/multiarch/memcmp.S.  */
+  /* Support sysdeps/x86_64/multiarch/memcmp.c.  */
   IFUNC_IMPL (i, name, memcmp,
 	      IFUNC_IMPL_ADD (array, i, memcmp,
 			      (HAS_ARCH_FEATURE (AVX2_Usable)
@@ -390,7 +390,7 @@  __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			      __wmemchr_avx2)
 	      IFUNC_IMPL_ADD (array, i, wmemchr, 1, __wmemchr_sse2))
 
-  /* Support sysdeps/x86_64/multiarch/wmemcmp.S.  */
+  /* Support sysdeps/x86_64/multiarch/wmemcmp.c.  */
   IFUNC_IMPL (i, name, wmemcmp,
 	      IFUNC_IMPL_ADD (array, i, wmemcmp,
 			      (HAS_ARCH_FEATURE (AVX2_Usable)
diff --git a/sysdeps/x86_64/multiarch/ifunc-memcmp.h b/sysdeps/x86_64/multiarch/ifunc-memcmp.h
new file mode 100644
index 0000000..6f76a93
--- /dev/null
+++ b/sysdeps/x86_64/multiarch/ifunc-memcmp.h
@@ -0,0 +1,45 @@ 
+/* Common definition for memcmp/wmemcmp ifunc selections.
+   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/>.  */
+
+# include <init-arch.h>
+
+extern __typeof (REDIRECT_NAME) OPTIMIZE (sse2) attribute_hidden;
+extern __typeof (REDIRECT_NAME) OPTIMIZE (ssse3) attribute_hidden;
+extern __typeof (REDIRECT_NAME) OPTIMIZE (sse4_1) attribute_hidden;
+extern __typeof (REDIRECT_NAME) OPTIMIZE (avx2_movbe) attribute_hidden;
+
+static inline void *
+IFUNC_SELECTOR (void)
+{
+  const struct cpu_features* cpu_features = __get_cpu_features ();
+
+  if (!CPU_FEATURES_ARCH_P (cpu_features, Prefer_No_VZEROUPPER)
+      && CPU_FEATURES_ARCH_P (cpu_features, AVX2_Usable)
+      && CPU_FEATURES_CPU_P (cpu_features, MOVBE)
+      && CPU_FEATURES_ARCH_P (cpu_features, AVX_Fast_Unaligned_Load))
+    return OPTIMIZE (avx2_movbe);
+
+  if (CPU_FEATURES_CPU_P (cpu_features, SSE4_1))
+    return OPTIMIZE (sse4_1);
+
+  if (CPU_FEATURES_CPU_P (cpu_features, SSSE3))
+    return OPTIMIZE (ssse3);
+
+  return OPTIMIZE (sse2);
+}
diff --git a/sysdeps/x86_64/multiarch/wmemcmp.S b/sysdeps/x86_64/multiarch/memcmp-sse2.S
similarity index 54%
rename from sysdeps/x86_64/multiarch/wmemcmp.S
rename to sysdeps/x86_64/multiarch/memcmp-sse2.S
index 94b25a2..72bea8b 100644
--- a/sysdeps/x86_64/multiarch/wmemcmp.S
+++ b/sysdeps/x86_64/multiarch/memcmp-sse2.S
@@ -1,6 +1,6 @@ 
-/* Multiple versions of wmemcmp
+/* memcmp with SSE2.
    All versions must be listed in ifunc-impl-list.c.
-   Copyright (C) 2011-2017 Free Software Foundation, Inc.
+   Copyright (C) 2010-2017 Free Software Foundation, Inc.
    Contributed by Intel Corporation.
    This file is part of the GNU C Library.
 
@@ -18,38 +18,16 @@ 
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-#include <sysdep.h>
-#include <init-arch.h>
-
-/* Define multiple versions only for the definition in libc. */
 #if IS_IN (libc)
-	.text
-ENTRY(wmemcmp)
-	.type	wmemcmp, @gnu_indirect_function
-	LOAD_RTLD_GLOBAL_RO_RDX
-	HAS_ARCH_FEATURE (Prefer_No_VZEROUPPER)
-	jnz	1f
-	HAS_ARCH_FEATURE (AVX2_Usable)
-	jz	1f
-	HAS_CPU_FEATURE (MOVBE)
-	jz	1f
-	HAS_ARCH_FEATURE (AVX_Fast_Unaligned_Load)
-	jz	1f
-	leaq	__wmemcmp_avx2_movbe(%rip), %rax
-	ret
-
-1:	HAS_CPU_FEATURE (SSSE3)
-	jnz	2f
-	leaq	__wmemcmp_sse2(%rip), %rax
-	ret
+# define memcmp __memcmp_sse2
 
-2:	HAS_CPU_FEATURE (SSE4_1)
-	jz	3f
-	leaq	__wmemcmp_sse4_1(%rip), %rax
-	ret
+# ifdef SHARED
+#  undef libc_hidden_builtin_def
+#  define libc_hidden_builtin_def(name)
+# endif
 
-3:	leaq	__wmemcmp_ssse3(%rip), %rax
-	ret
-
-END(wmemcmp)
+# undef weak_alias
+# define weak_alias(ignored1, ignored2)
 #endif
+
+#include <sysdeps/x86_64/memcmp.S>
diff --git a/sysdeps/x86_64/multiarch/memcmp.S b/sysdeps/x86_64/multiarch/memcmp.S
deleted file mode 100644
index 0c9804b..0000000
--- a/sysdeps/x86_64/multiarch/memcmp.S
+++ /dev/null
@@ -1,78 +0,0 @@ 
-/* Multiple versions of memcmp
-   All versions must be listed in ifunc-impl-list.c.
-   Copyright (C) 2010-2017 Free Software Foundation, Inc.
-   Contributed by Intel Corporation.
-   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/>.  */
-
-#include <sysdep.h>
-#include <init-arch.h>
-
-/* Define multiple versions only for the definition in libc. */
-#if IS_IN (libc)
-	.text
-ENTRY(memcmp)
-	.type	memcmp, @gnu_indirect_function
-	LOAD_RTLD_GLOBAL_RO_RDX
-	HAS_ARCH_FEATURE (Prefer_No_VZEROUPPER)
-	jnz	1f
-	HAS_ARCH_FEATURE (AVX2_Usable)
-	jz	1f
-	HAS_CPU_FEATURE (MOVBE)
-	jz	1f
-	HAS_ARCH_FEATURE (AVX_Fast_Unaligned_Load)
-	jz	1f
-	leaq	__memcmp_avx2_movbe(%rip), %rax
-	ret
-
-1:	HAS_CPU_FEATURE (SSSE3)
-	jnz	2f
-	leaq	__memcmp_sse2(%rip), %rax
-	ret
-
-2:	HAS_CPU_FEATURE (SSE4_1)
-	jz	3f
-	leaq	__memcmp_sse4_1(%rip), %rax
-	ret
-
-3:	leaq	__memcmp_ssse3(%rip), %rax
-	ret
-
-END(memcmp)
-
-# undef ENTRY
-# define ENTRY(name) \
-	.type __memcmp_sse2, @function; \
-	.p2align 4; \
-	.globl __memcmp_sse2; \
-	.hidden __memcmp_sse2; \
-	__memcmp_sse2: cfi_startproc; \
-	CALL_MCOUNT
-# undef END
-# define END(name) \
-	cfi_endproc; .size __memcmp_sse2, .-__memcmp_sse2
-
-# ifdef SHARED
-#  undef libc_hidden_builtin_def
-/* It doesn't make sense to send libc-internal memcmp calls through a PLT.
-   The speedup we get from using SSE4 instructions is likely eaten away
-   by the indirect call in the PLT.  */
-#  define libc_hidden_builtin_def(name) \
-	.globl __GI_memcmp; __GI_memcmp = __memcmp_sse2
-# endif
-#endif
-
-#include "../memcmp.S"
diff --git a/sysdeps/x86_64/multiarch/memcmp.c b/sysdeps/x86_64/multiarch/memcmp.c
new file mode 100644
index 0000000..b3e4ac3
--- /dev/null
+++ b/sysdeps/x86_64/multiarch/memcmp.c
@@ -0,0 +1,38 @@ 
+/* Multiple versions of memcmp.
+   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/>.  */
+
+/* Define multiple versions only for the definition in lib and for
+   DSO.  */
+#if IS_IN (libc)
+# define memcmp __redirect_memcmp
+# include <string.h>
+# undef memcmp
+
+# define SYMBOL_NAME memcmp
+# include "ifunc-memcmp.h"
+
+libc_ifunc_redirected (__redirect_memcmp, memcmp, IFUNC_SELECTOR ());
+# undef bcmp
+weak_alias (memcmp, bcmp)
+
+# ifdef SHARED
+__hidden_ver1 (memcmp, __GI_memcmp, __redirect_memcmp)
+  __attribute__ ((visibility ("hidden")));
+# endif
+#endif
diff --git a/sysdeps/x86_64/multiarch/wmemcmp.c b/sysdeps/x86_64/multiarch/wmemcmp.c
new file mode 100644
index 0000000..bbf6c83
--- /dev/null
+++ b/sysdeps/x86_64/multiarch/wmemcmp.c
@@ -0,0 +1,31 @@ 
+/* Multiple versions of wmemcmp
+   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/>.  */
+
+/* Define multiple versions only for the definition in lib and for
+   DSO.  */
+#if IS_IN (libc)
+# define wmemcmp __redirect_wmemcmp
+# include <wchar.h>
+# undef wmemcmp
+
+# define SYMBOL_NAME wmemcmp
+# include "ifunc-memcmp.h"
+
+libc_ifunc_redirected (__redirect_wmemcmp, wmemcmp, IFUNC_SELECTOR ());
+#endif