1 files changed, 101 insertions, 0 deletions
diff --git a/arch/riscv/lib/strlen_zbb.S b/arch/riscv/lib/strlen_zbb.S
new file mode 100644
index 0000000000..bd8fa4c0bd
--- /dev/null
+++ b/arch/riscv/lib/strlen_zbb.S
@@ -0,0 +1,101 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Taken from Linux arch/riscv/lib/strlen.S
+ */
+
+#include <linux/linkage.h>
+#include <asm/asm.h>
+
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+# define CZ	ctz
+# define SHIFT	srl
+#else
+# define CZ	clz
+# define SHIFT	sll
+#endif
+
+ENTRY(__strlen)
+WEAK(strlen)
+.option push
+.option arch,+zbb
+	/*
+	 * Returns
+	 *   a0 - string length
+	 *
+	 * Parameters
+	 *   a0 - String to measure
+	 *
+	 * Clobbers
+	 *   t0, t1, t2, t3
+	 */
+
+	/* Number of irrelevant bytes in the first word. */
+	andi	t2, a0, SZREG-1
+
+	/* Align pointer. */
+	andi	t0, a0, -SZREG
+
+	li	t3, SZREG
+	sub	t3, t3, t2
+	slli	t2, t2, 3
+
+	/* Get the first word.  */
+	REG_L	t1, 0(t0)
+
+	/*
+	 * Shift away the partial data we loaded to remove the irrelevant bytes
+	 * preceding the string with the effect of adding NUL bytes at the
+	 * end of the string's first word.
+	 */
+	SHIFT	t1, t1, t2
+
+	/* Convert non-NUL into 0xff and NUL into 0x00. */
+	orc.b	t1, t1
+
+	/* Convert non-NUL into 0x00 and NUL into 0xff. */
+	not	t1, t1
+
+	/*
+	 * Search for the first set bit (corresponding to a NUL byte in the
+	 * original chunk).
+	 */
+	CZ	t1, t1
+
+	/*
+	 * The first chunk is special: compare against the number
+	 * of valid bytes in this chunk.
+	 */
+	srli	a0, t1, 3
+	bgtu	t3, a0, 2f
+
+	/* Prepare for the word comparison loop. */
+	addi	t2, t0, SZREG
+	li	t3, -1
+
+	/*
+	 * Our critical loop is 4 instructions and processes data in
+	 * 4 byte or 8 byte chunks.
+	 */
+	.p2align 3
+1:
+	REG_L	t1, SZREG(t0)
+	addi	t0, t0, SZREG
+	orc.b	t1, t1
+	beq	t1, t3, 1b
+
+	not	t1, t1
+	CZ	t1, t1
+	srli	t1, t1, 3
+
+	/* Get number of processed bytes. */
+	sub	t2, t0, t2
+
+	/* Add number of characters in the first word.  */
+	add	a0, a0, t2
+
+	/* Add number of characters in the last word.  */
+	add	a0, a0, t1
+2:
+	ret
+.option pop
+END(__strlen)