riscv: Add Zbb support for building U-Boot
This patch adds ISA string to the -march to generate zbb instructions
for U-Boot binaries, along with optimized string functions introduced
from Linux kernel.
Signed-off-by: Yu Chien Peter Lin <peterlin@andestech.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>
diff --git a/arch/riscv/lib/strlen_zbb.S b/arch/riscv/lib/strlen_zbb.S
new file mode 100644
index 0000000..bd8fa4c
--- /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)