[PATCH 2/2] riscv: Add and use alignment-ignorant memcpy
Evan Green
evan@rivosinc.com
Mon Feb 6 19:48:19 GMT 2023
For CPU implementations that can perform unaligned accesses with little
or no performance penalty, create a memcpy implementation that does not
bother aligning buffers. It will use a block of integer registers, a
single integer register, and fall back to bytewise copy for the
remainder.
Signed-off-by: Evan Green <evan@rivosinc.com>
---
---
sysdeps/riscv/memcopy.h | 28 +++++
sysdeps/riscv/memcpy.c | 65 +++++++++++
sysdeps/riscv/memcpy_noalignment.S | 103 ++++++++++++++++++
sysdeps/unix/sysv/linux/riscv/Makefile | 4 +
.../unix/sysv/linux/riscv/memcpy-generic.c | 24 ++++
5 files changed, 224 insertions(+)
create mode 100644 sysdeps/riscv/memcopy.h
create mode 100644 sysdeps/riscv/memcpy.c
create mode 100644 sysdeps/riscv/memcpy_noalignment.S
create mode 100644 sysdeps/unix/sysv/linux/riscv/memcpy-generic.c
diff --git a/sysdeps/riscv/memcopy.h b/sysdeps/riscv/memcopy.h
new file mode 100644
index 0000000000..21f6081b5f
--- /dev/null
+++ b/sysdeps/riscv/memcopy.h
@@ -0,0 +1,28 @@
+/* memcopy.h -- definitions for memory copy functions. RISC-V version.
+ Copyright (C) 2023 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
+ <https://www.gnu.org/licenses/>. */
+
+#include <sysdeps/generic/memcopy.h>
+
+/*
+ * Redefine the generic memcpy implementation to __memcpy_generic, so
+ * the memcpy ifunc can select between generic and special versions.
+ * In rtld, don't bother with all the ifunciness.
+ */
+#if IS_IN (libc)
+#define MEMCPY __memcpy_generic
+#endif
diff --git a/sysdeps/riscv/memcpy.c b/sysdeps/riscv/memcpy.c
new file mode 100644
index 0000000000..1ba25ef976
--- /dev/null
+++ b/sysdeps/riscv/memcpy.c
@@ -0,0 +1,65 @@
+/* Multiple versions of memcpy.
+ All versions must be listed in ifunc-impl-list.c.
+ Copyright (C) 2017-2023 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
+ <https://www.gnu.org/licenses/>. */
+
+#if IS_IN (libc)
+/* Redefine memcpy so that the compiler won't complain about the type
+ mismatch with the IFUNC selector in strong_alias, below. */
+# undef memcpy
+# define memcpy __redirect_memcpy
+# include <string.h>
+#include <ifunc-init.h>
+#include <sys/hwprobe.h>
+
+#define INIT_ARCH()
+
+extern __typeof (__redirect_memcpy) __libc_memcpy;
+
+extern __typeof (__redirect_memcpy) __memcpy_generic attribute_hidden;
+extern __typeof (__redirect_memcpy) __memcpy_noalignment attribute_hidden;
+
+static inline __typeof (__redirect_memcpy) *
+select_memcpy_ifunc (void)
+{
+ INIT_ARCH ();
+
+ struct riscv_hwprobe pair;
+
+ pair.key = RISCV_HWPROBE_KEY_CPUPERF_0;
+ if (__riscv_hwprobe(&pair, 1, 0, NULL, 0) != 0)
+ return __memcpy_generic;
+
+ if ((pair.key > 0) &&
+ (pair.value & RISCV_HWPROBE_MISALIGNED_FAST) ==
+ RISCV_HWPROBE_MISALIGNED_FAST)
+ return __memcpy_noalignment;
+
+ return __memcpy_generic;
+}
+
+libc_ifunc (__libc_memcpy, select_memcpy_ifunc ());
+
+# undef memcpy
+strong_alias (__libc_memcpy, memcpy);
+# ifdef SHARED
+__hidden_ver1 (memcpy, __GI_memcpy, __redirect_memcpy)
+ __attribute__ ((visibility ("hidden"))) __attribute_copy__ (memcpy);
+# endif
+
+#endif
+
diff --git a/sysdeps/riscv/memcpy_noalignment.S b/sysdeps/riscv/memcpy_noalignment.S
new file mode 100644
index 0000000000..fe1d9213c4
--- /dev/null
+++ b/sysdeps/riscv/memcpy_noalignment.S
@@ -0,0 +1,103 @@
+/* memcpy for RISC-V, ignoring buffer alignment
+ Copyright (C) 2023 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
+ <https://www.gnu.org/licenses/>. */
+
+#include <sysdep.h>
+#include <sys/asm.h>
+
+/* void *memcpy(void *, const void *, size_t) */
+ENTRY (__memcpy_noalignment)
+ move t6, a0 /* Preserve return value */
+
+ /* Round down to the nearest "page" size */
+ andi a4, a2, ~((16*SZREG)-1)
+ beqz a4, 2f
+ add a3, a1, a4
+1:
+ /* Copy "pages" (chunks of 16 registers) */
+ REG_L a4, 0(a1)
+ REG_L a5, SZREG(a1)
+ REG_L a6, 2*SZREG(a1)
+ REG_L a7, 3*SZREG(a1)
+ REG_L t0, 4*SZREG(a1)
+ REG_L t1, 5*SZREG(a1)
+ REG_L t2, 6*SZREG(a1)
+ REG_L t3, 7*SZREG(a1)
+ REG_L t4, 8*SZREG(a1)
+ REG_L t5, 9*SZREG(a1)
+ REG_S a4, 0(t6)
+ REG_S a5, SZREG(t6)
+ REG_S a6, 2*SZREG(t6)
+ REG_S a7, 3*SZREG(t6)
+ REG_S t0, 4*SZREG(t6)
+ REG_S t1, 5*SZREG(t6)
+ REG_S t2, 6*SZREG(t6)
+ REG_S t3, 7*SZREG(t6)
+ REG_S t4, 8*SZREG(t6)
+ REG_S t5, 9*SZREG(t6)
+ REG_L a4, 10*SZREG(a1)
+ REG_L a5, 11*SZREG(a1)
+ REG_L a6, 12*SZREG(a1)
+ REG_L a7, 13*SZREG(a1)
+ REG_L t0, 14*SZREG(a1)
+ REG_L t1, 15*SZREG(a1)
+ addi a1, a1, 16*SZREG
+ REG_S a4, 10*SZREG(t6)
+ REG_S a5, 11*SZREG(t6)
+ REG_S a6, 12*SZREG(t6)
+ REG_S a7, 13*SZREG(t6)
+ REG_S t0, 14*SZREG(t6)
+ REG_S t1, 15*SZREG(t6)
+ addi t6, t6, 16*SZREG
+ bltu a1, a3, 1b
+ andi a2, a2, (16*SZREG)-1 /* Update count */
+
+2:
+ /* Remainder is smaller than a page, compute native word count */
+ beqz a2, 6f
+ andi a5, a2, ~(SZREG-1)
+ andi a2, a2, (SZREG-1)
+ add a3, a1, a5
+ /* Jump directly to byte copy if no words. */
+ beqz a5, 4f
+
+3:
+ /* Use single native register copy */
+ REG_L a4, 0(a1)
+ addi a1, a1, SZREG
+ REG_S a4, 0(t6)
+ addi t6, t6, SZREG
+ bltu a1, a3, 3b
+
+ /* Jump directly out if no more bytes */
+ beqz a2, 6f
+
+4:
+ /* Copy the last few individual bytes */
+ add a3, a1, a2
+5:
+ lb a4, 0(a1)
+ addi a1, a1, 1
+ sb a4, 0(t6)
+ addi t6, t6, 1
+ bltu a1, a3, 5b
+6:
+ ret
+
+END (__memcpy_noalignment)
+
+hidden_def (__memcpy_noalignment)
diff --git a/sysdeps/unix/sysv/linux/riscv/Makefile b/sysdeps/unix/sysv/linux/riscv/Makefile
index 45cc29e40d..aa9ea443d6 100644
--- a/sysdeps/unix/sysv/linux/riscv/Makefile
+++ b/sysdeps/unix/sysv/linux/riscv/Makefile
@@ -7,6 +7,10 @@ ifeq ($(subdir),stdlib)
gen-as-const-headers += ucontext_i.sym
endif
+ifeq ($(subdir),string)
+sysdep_routines += memcpy memcpy-generic memcpy_noalignment
+endif
+
abi-variants := ilp32 ilp32d lp64 lp64d
ifeq (,$(filter $(default-abi),$(abi-variants)))
diff --git a/sysdeps/unix/sysv/linux/riscv/memcpy-generic.c b/sysdeps/unix/sysv/linux/riscv/memcpy-generic.c
new file mode 100644
index 0000000000..0abe03f7f5
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/memcpy-generic.c
@@ -0,0 +1,24 @@
+/* Re-include the default memcpy implementation.
+ Copyright (C) 2023 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
+ <https://www.gnu.org/licenses/>. */
+
+#include <string.h>
+
+extern __typeof (memcpy) __memcpy_generic;
+hidden_proto(__memcpy_generic)
+
+#include <string/memcpy.c>
--
2.25.1
More information about the Libc-alpha
mailing list