v4.19.13 snapshot.
diff --git a/arch/arm64/lib/strlen.S b/arch/arm64/lib/strlen.S
new file mode 100644
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+/*
+ * Copyright (C) 2013 ARM Ltd.
+ * Copyright (C) 2013 Linaro.
+ *
+ * This code is based on glibc cortex strings work originally authored by Linaro
+ * and re-licensed under GPLv2 for the Linux kernel. The original code can
+ * be found @
+ *
+ * http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/
+ * files/head:/src/aarch64/
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+
+/*
+ * calculate the length of a string
+ *
+ * Parameters:
+ * x0 - const string pointer
+ * Returns:
+ * x0 - the return length of specific string
+ */
+
+/* Arguments and results. */
+srcin .req x0
+len .req x0
+
+/* Locals and temporaries. */
+src .req x1
+data1 .req x2
+data2 .req x3
+data2a .req x4
+has_nul1 .req x5
+has_nul2 .req x6
+tmp1 .req x7
+tmp2 .req x8
+tmp3 .req x9
+tmp4 .req x10
+zeroones .req x11
+pos .req x12
+
+#define REP8_01 0x0101010101010101
+#define REP8_7f 0x7f7f7f7f7f7f7f7f
+#define REP8_80 0x8080808080808080
+
+ENTRY(strlen)
+ mov zeroones, #REP8_01
+ bic src, srcin, #15
+ ands tmp1, srcin, #15
+ b.ne .Lmisaligned
+ /*
+ * NUL detection works on the principle that (X - 1) & (~X) & 0x80
+ * (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
+ * can be done in parallel across the entire word.
+ */
+ /*
+ * The inner loop deals with two Dwords at a time. This has a
+ * slightly higher start-up cost, but we should win quite quickly,
+ * especially on cores with a high number of issue slots per
+ * cycle, as we get much better parallelism out of the operations.
+ */
+.Lloop:
+ ldp data1, data2, [src], #16
+.Lrealigned:
+ sub tmp1, data1, zeroones
+ orr tmp2, data1, #REP8_7f
+ sub tmp3, data2, zeroones
+ orr tmp4, data2, #REP8_7f
+ bic has_nul1, tmp1, tmp2
+ bics has_nul2, tmp3, tmp4
+ ccmp has_nul1, #0, #0, eq /* NZCV = 0000 */
+ b.eq .Lloop
+
+ sub len, src, srcin
+ cbz has_nul1, .Lnul_in_data2
+CPU_BE( mov data2, data1 ) /*prepare data to re-calculate the syndrome*/
+ sub len, len, #8
+ mov has_nul2, has_nul1
+.Lnul_in_data2:
+ /*
+ * For big-endian, carry propagation (if the final byte in the
+ * string is 0x01) means we cannot use has_nul directly. The
+ * easiest way to get the correct byte is to byte-swap the data
+ * and calculate the syndrome a second time.
+ */
+CPU_BE( rev data2, data2 )
+CPU_BE( sub tmp1, data2, zeroones )
+CPU_BE( orr tmp2, data2, #REP8_7f )
+CPU_BE( bic has_nul2, tmp1, tmp2 )
+
+ sub len, len, #8
+ rev has_nul2, has_nul2
+ clz pos, has_nul2
+ add len, len, pos, lsr #3 /* Bits to bytes. */
+ ret
+
+.Lmisaligned:
+ cmp tmp1, #8
+ neg tmp1, tmp1
+ ldp data1, data2, [src], #16
+ lsl tmp1, tmp1, #3 /* Bytes beyond alignment -> bits. */
+ mov tmp2, #~0
+ /* Big-endian. Early bytes are at MSB. */
+CPU_BE( lsl tmp2, tmp2, tmp1 ) /* Shift (tmp1 & 63). */
+ /* Little-endian. Early bytes are at LSB. */
+CPU_LE( lsr tmp2, tmp2, tmp1 ) /* Shift (tmp1 & 63). */
+
+ orr data1, data1, tmp2
+ orr data2a, data2, tmp2
+ csinv data1, data1, xzr, le
+ csel data2, data2, data2a, le
+ b .Lrealigned
+ENDPIPROC(strlen)