glibc/sysdeps/aarch64/strnlen.S

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/* strnlen - calculate the length of a string with limit.
Copyright (C) 2013-2015 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library. If not, see
<http://www.gnu.org/licenses/>. */
#include <sysdep.h>
/* Assumptions:
*
* ARMv8-a, AArch64
*/
/* Arguments and results. */
#define srcin x0
#define len x0
#define limit x1
/* Locals and temporaries. */
#define src x2
#define data1 x3
#define data2 x4
#define data2a x5
#define has_nul1 x6
#define has_nul2 x7
#define tmp1 x8
#define tmp2 x9
#define tmp3 x10
#define tmp4 x11
#define zeroones x12
#define pos x13
#define limit_wd x14
#define REP8_01 0x0101010101010101
#define REP8_7f 0x7f7f7f7f7f7f7f7f
#define REP8_80 0x8080808080808080
ENTRY_ALIGN_AND_PAD (__strnlen, 6, 9)
cbz limit, L(hit_limit)
mov zeroones, #REP8_01
bic src, srcin, #15
ands tmp1, srcin, #15
b.ne L(misaligned)
/* Calculate the number of full and partial words -1. */
sub limit_wd, limit, #1 /* Limit != 0, so no underflow. */
lsr limit_wd, limit_wd, #4 /* Convert to Qwords. */
/* 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. */
/* Start of critial section -- keep to one 64Byte cache line. */
L(loop):
ldp data1, data2, [src], #16
L(realigned):
sub tmp1, data1, zeroones
orr tmp2, data1, #REP8_7f
sub tmp3, data2, zeroones
orr tmp4, data2, #REP8_7f
bic has_nul1, tmp1, tmp2
bic has_nul2, tmp3, tmp4
subs limit_wd, limit_wd, #1
orr tmp1, has_nul1, has_nul2
ccmp tmp1, #0, #0, pl /* NZCV = 0000 */
b.eq L(loop)
/* End of critical section -- keep to one 64Byte cache line. */
orr tmp1, has_nul1, has_nul2
cbz tmp1, L(hit_limit) /* No null in final Qword. */
/* We know there's a null in the final Qword. The easiest thing
to do now is work out the length of the string and return
MIN (len, limit). */
sub len, src, srcin
cbz has_nul1, L(nul_in_data2)
#ifdef __AARCH64EB__
mov data2, data1
#endif
sub len, len, #8
mov has_nul2, has_nul1
L(nul_in_data2):
#ifdef __AARCH64EB__
/* 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. */
rev data2, data2
sub tmp1, data2, zeroones
orr tmp2, data2, #REP8_7f
bic has_nul2, tmp1, tmp2
#endif
sub len, len, #8
rev has_nul2, has_nul2
clz pos, has_nul2
add len, len, pos, lsr #3 /* Bits to bytes. */
cmp len, limit
csel len, len, limit, ls /* Return the lower value. */
RET
L(misaligned):
/* Deal with a partial first word.
We're doing two things in parallel here;
1) Calculate the number of words (but avoiding overflow if
limit is near ULONG_MAX) - to do this we need to work out
limit + tmp1 - 1 as a 65-bit value before shifting it;
2) Load and mask the initial data words - we force the bytes
before the ones we are interested in to 0xff - this ensures
early bytes will not hit any zero detection. */
sub limit_wd, limit, #1
neg tmp4, tmp1
cmp tmp1, #8
and tmp3, limit_wd, #15
lsr limit_wd, limit_wd, #4
mov tmp2, #~0
ldp data1, data2, [src], #16
lsl tmp4, tmp4, #3 /* Bytes beyond alignment -> bits. */
add tmp3, tmp3, tmp1
#ifdef __AARCH64EB__
/* Big-endian. Early bytes are at MSB. */
lsl tmp2, tmp2, tmp4 /* Shift (tmp1 & 63). */
#else
/* Little-endian. Early bytes are at LSB. */
lsr tmp2, tmp2, tmp4 /* Shift (tmp1 & 63). */
#endif
add limit_wd, limit_wd, tmp3, lsr #4
orr data1, data1, tmp2
orr data2a, data2, tmp2
csinv data1, data1, xzr, le
csel data2, data2, data2a, le
b L(realigned)
L(hit_limit):
mov len, limit
RET
END (__strnlen)
Use libc_hidden_proto / libc_hidden_def with __strnlen. Various code in glibc uses __strnlen instead of strnlen for namespace reasons. However, __strnlen does not use libc_hidden_proto / libc_hidden_def (as is normally done for any function defined and called within the same library, whether or not exported from the library and whatever namespace it is in), so the compiler does not know that those calls are to a function within libc. This patch uses libc_hidden_proto / libc_hidden_def with __strnlen. On x86_64, it makes no difference to the installed stripped shared libraries. On 32-bit x86, it causes __strnlen calls to go to the same place as strnlen calls (the fallback strnlen implementation), rather than through a PLT entry for the strnlen IFUNC; I'm not sure of the logic behind when calls from within libc should use IFUNCs versus when they should go direct to a particular function implementation, but clearly it doesn't make sense for strnlen and __strnlen to be handled differently in this regard. Tested for x86_64 and x86 (testsuite, and comparison of installed shared libraries as described above). * string/strnlen.c [!STRNLEN] (__strnlen): Use libc_hidden_def. * include/string.h (__strnlen): Use libc_hidden_proto. * sysdeps/aarch64/strnlen.S (__strnlen): Use libc_hidden_def. * sysdeps/i386/i686/multiarch/strnlen-c.c [SHARED] (libc_hidden_def): Define __GI___strnlen as well as __GI_strnlen. * sysdeps/powerpc/powerpc32/power4/multiarch/strnlen-power7.S (libc_hidden_def): Undefine and redefine. * sysdeps/powerpc/powerpc32/power4/multiarch/strnlen-ppc32.c [SHARED] (libc_hidden_def): Define __GI___strnlen as well as __GI_strnlen. * sysdeps/powerpc/powerpc32/power7/strnlen.S (__strnlen): Use libc_hidden_def. * sysdeps/tile/tilegx/strnlen.c (__strnlen): Likewise.
2015-06-02 20:24:25 +00:00
libc_hidden_def (__strnlen)
weak_alias (__strnlen, strnlen)
libc_hidden_def (strnlen)