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/strlen.S b/libc/arch-arm64/default/bionic/strlen.S
new file mode 100644
index 0000000..07c5294
--- /dev/null
+++ b/libc/arch-arm64/default/bionic/strlen.S
@@ -0,0 +1,227 @@
+/* Copyright (c) 2013-2015, Linaro Limited
+ All rights reserved.
+
+ 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 Linaro 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, unaligned accesses, min page size 4k.
+ */
+
+#include <private/bionic_asm.h>
+
+/* To test the page crossing code path more thoroughly, compile with
+ -DTEST_PAGE_CROSS - this will force all calls through the slower
+ entry path. This option is not intended for production use. */
+
+/* Arguments and results. */
+#define srcin x0
+#define len x0
+
+/* Locals and temporaries. */
+#define src x1
+#define data1 x2
+#define data2 x3
+#define has_nul1 x4
+#define has_nul2 x5
+#define tmp1 x4
+#define tmp2 x5
+#define tmp3 x6
+#define tmp4 x7
+#define zeroones x8
+
+#define L(l) .L ## l
+
+ /* 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. A faster check
+ (X - 1) & 0x80 is zero for non-NUL ASCII characters, but gives
+ false hits for characters 129..255. */
+
+#define REP8_01 0x0101010101010101
+#define REP8_7f 0x7f7f7f7f7f7f7f7f
+#define REP8_80 0x8080808080808080
+
+#ifdef TEST_PAGE_CROSS
+# define MIN_PAGE_SIZE 15
+#else
+# define MIN_PAGE_SIZE 4096
+#endif
+
+ /* Since strings are short on average, we check the first 16 bytes
+ of the string for a NUL character. In order to do an unaligned ldp
+ safely we have to do a page cross check first. If there is a NUL
+ byte we calculate the length from the 2 8-byte words using
+ conditional select to reduce branch mispredictions (it is unlikely
+ strlen will be repeatedly called on strings with the same length).
+
+ If the string is longer than 16 bytes, we align src so don't need
+ further page cross checks, and process 32 bytes per iteration
+ using the fast NUL check. If we encounter non-ASCII characters,
+ fallback to a second loop using the full NUL check.
+
+ If the page cross check fails, we read 16 bytes from an aligned
+ address, remove any characters before the string, and continue
+ in the main loop using aligned loads. Since strings crossing a
+ page in the first 16 bytes are rare (probability of
+ 16/MIN_PAGE_SIZE ~= 0.4%), this case does not need to be optimized.
+
+ AArch64 systems have a minimum page size of 4k. We don't bother
+ checking for larger page sizes - the cost of setting up the correct
+ page size is just not worth the extra gain from a small reduction in
+ the cases taking the slow path. Note that we only care about
+ whether the first fetch, which may be misaligned, crosses a page
+ boundary. */
+
+ENTRY(strlen_default)
+ and tmp1, srcin, MIN_PAGE_SIZE - 1
+ mov zeroones, REP8_01
+ cmp tmp1, MIN_PAGE_SIZE - 16
+ b.gt L(page_cross)
+ ldp data1, data2, [srcin]
+#ifdef __AARCH64EB__
+ /* For big-endian, carry propagation (if the final byte in the
+ string is 0x01) means we cannot use has_nul1/2 directly.
+ Since we expect strings to be small and early-exit,
+ byte-swap the data now so has_null1/2 will be correct. */
+ rev data1, data1
+ rev data2, data2
+#endif
+ sub tmp1, data1, zeroones
+ orr tmp2, data1, REP8_7f
+ sub tmp3, data2, zeroones
+ orr tmp4, data2, REP8_7f
+ bics has_nul1, tmp1, tmp2
+ bic has_nul2, tmp3, tmp4
+ ccmp has_nul2, 0, 0, eq
+ beq L(main_loop_entry)
+
+ /* Enter with C = has_nul1 == 0. */
+ csel has_nul1, has_nul1, has_nul2, cc
+ mov len, 8
+ rev has_nul1, has_nul1
+ clz tmp1, has_nul1
+ csel len, xzr, len, cc
+ add len, len, tmp1, lsr 3
+ ret
+
+ /* The inner loop processes 32 bytes per iteration and uses the fast
+ NUL check. If we encounter non-ASCII characters, use a second
+ loop with the accurate NUL check. */
+ .p2align 4
+L(main_loop_entry):
+ bic src, srcin, 15
+ sub src, src, 16
+L(main_loop):
+ ldp data1, data2, [src, 32]!
+.Lpage_cross_entry:
+ sub tmp1, data1, zeroones
+ sub tmp3, data2, zeroones
+ orr tmp2, tmp1, tmp3
+ tst tmp2, zeroones, lsl 7
+ bne 1f
+ ldp data1, data2, [src, 16]
+ sub tmp1, data1, zeroones
+ sub tmp3, data2, zeroones
+ orr tmp2, tmp1, tmp3
+ tst tmp2, zeroones, lsl 7
+ beq L(main_loop)
+ add src, src, 16
+1:
+ /* The fast check failed, so do the slower, accurate NUL check. */
+ orr tmp2, data1, REP8_7f
+ orr tmp4, data2, REP8_7f
+ bics has_nul1, tmp1, tmp2
+ bic has_nul2, tmp3, tmp4
+ ccmp has_nul2, 0, 0, eq
+ beq L(nonascii_loop)
+
+ /* Enter with C = has_nul1 == 0. */
+L(tail):
+#ifdef __AARCH64EB__
+ /* For big-endian, carry propagation (if the final byte in the
+ string is 0x01) means we cannot use has_nul1/2 directly. The
+ easiest way to get the correct byte is to byte-swap the data
+ and calculate the syndrome a second time. */
+ csel data1, data1, data2, cc
+ rev data1, data1
+ sub tmp1, data1, zeroones
+ orr tmp2, data1, REP8_7f
+ bic has_nul1, tmp1, tmp2
+#else
+ csel has_nul1, has_nul1, has_nul2, cc
+#endif
+ sub len, src, srcin
+ rev has_nul1, has_nul1
+ add tmp2, len, 8
+ clz tmp1, has_nul1
+ csel len, len, tmp2, cc
+ add len, len, tmp1, lsr 3
+ ret
+
+L(nonascii_loop):
+ ldp data1, data2, [src, 16]!
+ sub tmp1, data1, zeroones
+ orr tmp2, data1, REP8_7f
+ sub tmp3, data2, zeroones
+ orr tmp4, data2, REP8_7f
+ bics has_nul1, tmp1, tmp2
+ bic has_nul2, tmp3, tmp4
+ ccmp has_nul2, 0, 0, eq
+ bne L(tail)
+ ldp data1, data2, [src, 16]!
+ sub tmp1, data1, zeroones
+ orr tmp2, data1, REP8_7f
+ sub tmp3, data2, zeroones
+ orr tmp4, data2, REP8_7f
+ bics has_nul1, tmp1, tmp2
+ bic has_nul2, tmp3, tmp4
+ ccmp has_nul2, 0, 0, eq
+ beq L(nonascii_loop)
+ b L(tail)
+
+ /* Load 16 bytes from [srcin & ~15] and force the bytes that precede
+ srcin to 0x7f, so we ignore any NUL bytes before the string.
+ Then continue in the aligned loop. */
+L(page_cross):
+ bic src, srcin, 15
+ ldp data1, data2, [src]
+ lsl tmp1, srcin, 3
+ mov tmp4, -1
+#ifdef __AARCH64EB__
+ /* Big-endian. Early bytes are at MSB. */
+ lsr tmp1, tmp4, tmp1 /* Shift (tmp1 & 63). */
+#else
+ /* Little-endian. Early bytes are at LSB. */
+ lsl tmp1, tmp4, tmp1 /* Shift (tmp1 & 63). */
+#endif
+ orr tmp1, tmp1, REP8_80
+ orn data1, data1, tmp1
+ orn tmp2, data2, tmp1
+ tst srcin, 8
+ csel data1, data1, tmp4, eq
+ csel data2, data2, tmp2, eq
+ b L(page_cross_entry)
+
+END(strlen_default)