libs/libc/risc-v: Add optimized strlcpy.

Add word-at-a-time strlcpy using DETECTNULL for both the copy phase
and the strlen tail when truncated.  The copy loop aligns src and
processes a register at a time, falling to bytewise for the last word
containing the terminator.  When truncated, the remaining src length
is measured with a second word-at-a-time loop.

strlcpy has 46 call sites in a typical kernel image (more than strcpy)
and is not covered by newlib OPTSPEED, making it a high-value target.

Assisted-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
Signed-off-by: ganjing <ganjing@xiaomi.com>

libs/libc/machine/risc-v/CMakeLists.txt

@@ -84,6 +84,10 @@ if(CONFIG_RISCV_STRNCMP)
   list(APPEND SRCS arch_strncmp.S)
 endif()
 
+if(CONFIG_RISCV_STRLCPY)
+  list(APPEND SRCS arch_strlcpy.S)
+endif()
+
 if(CONFIG_RISCV_STRCAT)
   list(APPEND SRCS arch_strcat.S)
 endif()

libs/libc/machine/risc-v/Kconfig

@@ -24,6 +24,7 @@ config RISCV_STRING_FUNCTION
 	select RISCV_STRRCHR
 	select RISCV_STRNCMP
 	select RISCV_STRCAT
+	select RISCV_STRLCPY
 
 config RISCV_MEMCPY
 	bool "Enable optimized memcpy() for RISC-V"
@@ -159,3 +160,11 @@ config RISCV_STRCAT
 	depends on ARCH_TOOLCHAIN_GNU
 	---help---
 		Enable optimized RISC-V specific strcat() library function
+
+config RISCV_STRLCPY
+	bool "Enable optimized strlcpy() for RISC-V"
+	default n
+	select LIBC_ARCH_STRLCPY
+	depends on ARCH_TOOLCHAIN_GNU
+	---help---
+		Enable optimized RISC-V specific strlcpy() library function

libs/libc/machine/risc-v/Make.defs

@@ -84,6 +84,10 @@ ifeq ($(CONFIG_RISCV_STRNCMP),y)
 ASRCS += arch_strncmp.S
 endif
 
+ifeq ($(CONFIG_RISCV_STRLCPY),y)
+ASRCS += arch_strlcpy.S
+endif
+
 ifeq ($(CONFIG_RISCV_STRCAT),y)
 ASRCS += arch_strcat.S
 endif

libs/libc/machine/risc-v/arch_strlcpy.S

@@ -0,0 +1,201 @@
+/****************************************************************************
+ * libs/libc/machine/risc-v/arch_strlcpy.S
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ ****************************************************************************/
+
+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRLCPY
+
+#include "asm.h"
+
+.text
+.global ARCH_LIBCFUN(strlcpy)
+.type	ARCH_LIBCFUN(strlcpy), @function
+.align	2
+
+/************************************************************************************
+ * Name: strlcpy
+ *
+ * size_t strlcpy(char *dst, const char *src, size_t size)
+ *
+ * Copy at most size-1 bytes from src to dst, null-terminate (if size > 0),
+ * and return strlen(src).  Word-at-a-time DETECTNULL for both the copy
+ * phase and the strlen tail when truncated.
+ ************************************************************************************/
+
+/* DETECTNULL constants loaded from .srodata */
+
+	.section .srodata, "a"
+	.align	SZREG
+.Lmask_01:
+#if SZREG == 8
+	.dword	0x0101010101010101
+#else
+	.word	0x01010101
+#endif
+.Lmask_80:
+#if SZREG == 8
+	.dword	0x8080808080808080
+#else
+	.word	0x80808080
+#endif
+
+	.text
+
+ARCH_LIBCFUN(strlcpy):
+	.cfi_sections .debug_frame
+	.cfi_startproc
+
+	mv	t6, a1			/* save src start for return value */
+
+	/* size == 0: skip copy, just measure src */
+
+	beqz	a2, .Lmeasure
+
+	addi	a2, a2, -1		/* reserve space for null terminator */
+
+	/* Bytewise copy head: align src to SZREG boundary */
+
+.Lcopy_head:
+	beqz	a2, .Ltruncated
+	andi	t0, a1, SZREG-1
+	beqz	t0, .Lcopy_word_setup
+	lbu	t0, 0(a1)
+	sb	t0, 0(a0)
+	beqz	t0, .Ldone
+	addi	a0, a0, 1
+	addi	a1, a1, 1
+	addi	a2, a2, -1
+	j	.Lcopy_head
+
+.Lcopy_word_setup:
+	/* Load DETECTNULL masks */
+
+	lla	t2, .Lmask_01
+	lla	t3, .Lmask_80
+	REG_L	t2, 0(t2)		/* t2 = 0x0101...01 */
+	REG_L	t3, 0(t3)		/* t3 = 0x8080...80 */
+
+	/* Word copy loop: need at least SZREG bytes remaining in size */
+
+	li	t4, SZREG
+
+.Lcopy_word:
+	bltu	a2, t4, .Lcopy_tail
+	REG_L	t0, 0(a1)
+
+	/* DETECTNULL: (word - 0x0101..01) & ~word & 0x8080..80 */
+
+	sub	t1, t0, t2
+	not	t5, t0
+	and	t1, t1, t5
+	and	t1, t1, t3
+	bnez	t1, .Lcopy_last_word
+
+	/* No null in this word, store it */
+
+	REG_S	t0, 0(a0)
+	addi	a0, a0, SZREG
+	addi	a1, a1, SZREG
+	sub	a2, a2, t4
+	j	.Lcopy_word
+
+.Lcopy_last_word:
+	/* Null found within word: copy bytes until null */
+
+	lbu	t0, 0(a1)
+	sb	t0, 0(a0)
+	beqz	t0, .Ldone
+	addi	a0, a0, 1
+	addi	a1, a1, 1
+	j	.Lcopy_last_word
+
+.Lcopy_tail:
+	/* Less than SZREG bytes of size left: bytewise copy */
+
+	beqz	a2, .Ltruncated
+	lbu	t0, 0(a1)
+	sb	t0, 0(a0)
+	beqz	t0, .Ldone
+	addi	a0, a0, 1
+	addi	a1, a1, 1
+	addi	a2, a2, -1
+	j	.Lcopy_tail
+
+.Ltruncated:
+	/* Null-terminate dst */
+
+	sb	zero, 0(a0)
+
+	/* Measure remaining src length with word-at-a-time */
+
+.Lmeasure:
+	/* Bytewise to align src */
+
+	andi	t0, a1, SZREG-1
+	beqz	t0, .Lmeasure_word_setup
+
+.Lmeasure_head:
+	lbu	t0, 0(a1)
+	beqz	t0, .Lreturn
+	addi	a1, a1, 1
+	andi	t0, a1, SZREG-1
+	bnez	t0, .Lmeasure_head
+
+.Lmeasure_word_setup:
+	/* Load masks if not already loaded (from truncated path) */
+
+	lla	t2, .Lmask_01
+	lla	t3, .Lmask_80
+	REG_L	t2, 0(t2)
+	REG_L	t3, 0(t3)
+
+.Lmeasure_word:
+	REG_L	t0, 0(a1)
+	sub	t1, t0, t2
+	not	t5, t0
+	and	t1, t1, t5
+	and	t1, t1, t3
+	bnez	t1, .Lmeasure_tail
+	addi	a1, a1, SZREG
+	j	.Lmeasure_word
+
+.Lmeasure_tail:
+	/* Find exact null position */
+
+	lbu	t0, 0(a1)
+	beqz	t0, .Lreturn
+	addi	a1, a1, 1
+	j	.Lmeasure_tail
+
+.Ldone:
+	/* Normal completion: null found during copy */
+
+.Lreturn:
+	/* Return strlen(src) = current src pos - original start */
+
+	sub	a0, a1, t6
+	ret
+
+	.cfi_endproc
+	.size	ARCH_LIBCFUN(strlcpy), .-ARCH_LIBCFUN(strlcpy)
+
+#endif