[PW_SID:1095491] [v2] riscv: lib: add strrchr() zbb implementation

arch/riscv/lib/strrchr.S

@@ -6,13 +6,17 @@
 
 #include <linux/linkage.h>
 #include <asm/asm.h>
+#include <asm/alternative-macros.h>
+#include <asm/hwcap.h>
 
 /* char *strrchr(const char *s, int c) */
 SYM_FUNC_START(strrchr)
+	__ALTERNATIVE_CFG("nop", "j strrchr_zbb", 0, RISCV_ISA_EXT_ZBB,
+		IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB))
 	/*
 	 * Parameters
 	 *	a0 - The string to be searched
-	 *	a1 - The character to seaerch for
+	 *	a1 - The character to search for
 	 *
 	 * Returns
 	 *	a0 - Address of last occurrence of 'c' or 0
@@ -31,7 +35,129 @@ SYM_FUNC_START(strrchr)
 	addi	t1, t1, 1
 	bnez	t0, 1b
 	ret
-SYM_FUNC_END(strrchr)
 
+/*
+ * Variant of strrchr using the ZBB extension if available
+ */
+#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)
+strrchr_zbb:
+.option push
+.option arch,+zbb
+	/*
+	 * Parameters
+	 *	a0 - The string to be searched
+	 *	a1 - The character to search for
+	 *
+	 * Returns
+	 *	a0 - Address of last occurrence of 'c' or 0
+	 *
+	 * Clobbers
+	 *	t0, t1, t2, t3, t4, t5, t6
+	 */
+	andi	a1, a1, 0xff
+	mv	t1, a0
+	li	a0, 0
+	beqz	a1, .Lfind_end_zbb
+
+	slli	t5, a1, 8
+	or	t5, t5, a1
+	slli	t2, t5, 16
+	or	t5, t5, t2
+#if __riscv_xlen == 64
+	slli	t2, t5, 32
+	or	t5, t5, t2
+#endif
+
+	andi	t2, t1, SZREG-1
+	bnez	t2, .Lmisaligned_start
+
+.Lmain_loop_pre:
+	li	t4, -1
+
+	.balign 16
+.Lmain_loop:
+	REG_L	t0, 0(t1)
+	addi	t1, t1, SZREG
+	xor	t6, t0, t5
+	orc.b	t2, t0
+	orc.b	t6, t6
+	and	t3, t2, t6
+	beq	t3, t4, .Lmain_loop
+
+	not	t2, t2
+	not	t6, t6
+
+	beqz	t2, .Lonly_matches
+
+	addi	t1, t1, -SZREG
+	ctz	t3, t2
+	sll	t4, t4, t3
+	andn	t6, t6, t4
+	beqz	t6, .Ldone
+
+	clz	t3, t6
+	srli	t3, t3, 3
+	xori	t3, t3, SZREG-1
+	add	a0, t1, t3
+.Ldone:
+	ret
+
+.Lonly_matches:
+	clz	t3, t6
+	srli	t3, t3, 3
+	not	t3, t3
+	add	a0, t1, t3
+	j	.Lmain_loop
+
+.Lfind_end_zbb:
+	andi	t2, t1, SZREG-1
+	bnez	t2, .Lmisaligned_end_start
+
+.Lfind_end_pre:
+	li	t4, -1
+
+	.balign 16
+.Lfind_end_loop:
+	REG_L	t0, 0(t1)
+	addi	t1, t1, SZREG
+	orc.b	t2, t0
+	beq	t2, t4, .Lfind_end_loop
+
+	addi	t1, t1, -SZREG
+	not	t2, t2
+	ctz	t3, t2
+	srli	t3, t3, 3
+	add	a0, t1, t3
+	ret
+
+.Lfound_zero:
+	mv	a0, t1
+	ret
+.Lmisaligned_start:
+	ori	t2, t1, SZREG-1
+	addi	t2, t2, 1
+.Lalign_loop:
+	lbu	t0, 0(t1)
+	beqz	t0, .Ldone
+	bne	t0, a1, 1f
+	mv	a0, t1
+1:
+	addi	t1, t1, 1
+	bne	t1, t2, .Lalign_loop
+	j	.Lmain_loop_pre
+
+.Lmisaligned_end_start:
+	ori	t2, t1, SZREG-1
+	addi	t2, t2, 1
+.Lfind_end_align:
+	lbu	t0, 0(t1)
+	beqz	t0, .Lfound_zero
+	addi	t1, t1, 1
+	bne	t1, t2, .Lfind_end_align
+	j	.Lfind_end_pre
+
+.option pop
+#endif
+SYM_FUNC_END(strrchr)
 SYM_FUNC_ALIAS_WEAK(__pi_strrchr, strrchr)
 EXPORT_SYMBOL(strrchr)