Add arm64 string.h function implementations for use with hardware supporting MTE.
As it turns out, our "generic" arm64 implementations of certain string.h
functions are not actually generic, since they will eagerly read memory
possibly outside of the bounds of an MTE granule, which may lead to a segfault
on MTE-enabled hardware. Therefore, move the implementations into a "default"
directory and use ifuncs to select between them and a new set of "mte"
implementations, conditional on whether the hardware and kernel support MTE.
The MTE implementations are currently naive implementations written in C
but will later be replaced with a set of optimized assembly implementations.
Bug: 135772972
Change-Id: Ife37c4e0e6fd60ff20a34594cc09c541af4d1dd7
diff --git a/libc/arch-arm64/default/bionic/memchr.S b/libc/arch-arm64/default/bionic/memchr.S
new file mode 100644
index 0000000..7fbcc8f
--- /dev/null
+++ b/libc/arch-arm64/default/bionic/memchr.S
@@ -0,0 +1,164 @@
+/*
+ *
+ Copyright (c) 2014, ARM Limited
+ All rights Reserved.
+ Copyright (c) 2014, Linaro Ltd.
+
+ Redistribution and use in source and binary forms, with or without
+ modification, are permitted provided that the following conditions are met:
+ * Redistributions of source code must retain the above copyright
+ notice, this list of conditions and the following disclaimer.
+ * Redistributions in binary form must reproduce the above copyright
+ notice, this list of conditions and the following disclaimer in the
+ documentation and/or other materials provided with the distribution.
+ * Neither the name of the company nor the names of its contributors
+ may be used to endorse or promote products derived from this
+ software without specific prior written permission.
+
+ THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+/* Assumptions:
+ *
+ * ARMv8-a, AArch64
+ * Neon Available.
+ */
+
+#include <private/bionic_asm.h>
+
+/* Arguments and results. */
+#define srcin x0
+#define chrin w1
+#define cntin x2
+
+#define result x0
+
+#define src x3
+#define tmp x4
+#define wtmp2 w5
+#define synd x6
+#define soff x9
+#define cntrem x10
+
+#define vrepchr v0
+#define vdata1 v1
+#define vdata2 v2
+#define vhas_chr1 v3
+#define vhas_chr2 v4
+#define vrepmask v5
+#define vend v6
+
+/*
+ * Core algorithm:
+ *
+ * For each 32-byte chunk we calculate a 64-bit syndrome value, with two bits
+ * per byte. For each tuple, bit 0 is set if the relevant byte matched the
+ * requested character and bit 1 is not used (faster than using a 32bit
+ * syndrome). Since the bits in the syndrome reflect exactly the order in which
+ * things occur in the original string, counting trailing zeros allows to
+ * identify exactly which byte has matched.
+ */
+
+ENTRY(memchr_default)
+ /*
+ * Magic constant 0x40100401 allows us to identify which lane matches
+ * the requested byte.
+ */
+ cbz cntin, .Lzero_length
+ mov wtmp2, #0x0401
+ movk wtmp2, #0x4010, lsl #16
+ dup vrepchr.16b, chrin
+ /* Work with aligned 32-byte chunks */
+ bic src, srcin, #31
+ dup vrepmask.4s, wtmp2
+ ands soff, srcin, #31
+ and cntrem, cntin, #31
+ b.eq .Lloop
+
+ /*
+ * Input string is not 32-byte aligned. We calculate the syndrome
+ * value for the aligned 32 bytes block containing the first bytes
+ * and mask the irrelevant part.
+ */
+
+ ld1 {vdata1.16b, vdata2.16b}, [src], #32
+ sub tmp, soff, #32
+ adds cntin, cntin, tmp
+ cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b
+ cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b
+ and vhas_chr1.16b, vhas_chr1.16b, vrepmask.16b
+ and vhas_chr2.16b, vhas_chr2.16b, vrepmask.16b
+ addp vend.16b, vhas_chr1.16b, vhas_chr2.16b /* 256->128 */
+ addp vend.16b, vend.16b, vend.16b /* 128->64 */
+ mov synd, vend.d[0]
+ /* Clear the soff*2 lower bits */
+ lsl tmp, soff, #1
+ lsr synd, synd, tmp
+ lsl synd, synd, tmp
+ /* The first block can also be the last */
+ b.ls .Lmasklast
+ /* Have we found something already? */
+ cbnz synd, .Ltail
+
+.Lloop:
+ ld1 {vdata1.16b, vdata2.16b}, [src], #32
+ subs cntin, cntin, #32
+ cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b
+ cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b
+ /* If we're out of data we finish regardless of the result */
+ b.ls .Lend
+ /* Use a fast check for the termination condition */
+ orr vend.16b, vhas_chr1.16b, vhas_chr2.16b
+ addp vend.2d, vend.2d, vend.2d
+ mov synd, vend.d[0]
+ /* We're not out of data, loop if we haven't found the character */
+ cbz synd, .Lloop
+
+.Lend:
+ /* Termination condition found, let's calculate the syndrome value */
+ and vhas_chr1.16b, vhas_chr1.16b, vrepmask.16b
+ and vhas_chr2.16b, vhas_chr2.16b, vrepmask.16b
+ addp vend.16b, vhas_chr1.16b, vhas_chr2.16b /* 256->128 */
+ addp vend.16b, vend.16b, vend.16b /* 128->64 */
+ mov synd, vend.d[0]
+ /* Only do the clear for the last possible block */
+ b.hi .Ltail
+
+.Lmasklast:
+ /* Clear the (32 - ((cntrem + soff) % 32)) * 2 upper bits */
+ add tmp, cntrem, soff
+ and tmp, tmp, #31
+ sub tmp, tmp, #32
+ neg tmp, tmp, lsl #1
+ lsl synd, synd, tmp
+ lsr synd, synd, tmp
+
+.Ltail:
+ /* Count the trailing zeros using bit reversing */
+ rbit synd, synd
+ /* Compensate the last post-increment */
+ sub src, src, #32
+ /* Check that we have found a character */
+ cmp synd, #0
+ /* And count the leading zeros */
+ clz synd, synd
+ /* Compute the potential result */
+ add result, src, synd, lsr #1
+ /* Select result or NULL */
+ csel result, xzr, result, eq
+ ret
+
+.Lzero_length:
+ mov result, xzr
+ ret
+END(memchr_default)