It adds vectorized ChaCha20 implementation based on libgcrypt
cipher/chacha20-amd64-avx2.S. It is used only if AVX2 is supported
and enabled by the architecture.
As for generic implementation, the last step that XOR with the
input is omited. The final state register clearing is also
omitted.
On a Ryzen 9 5900X it shows the following improvements (using
formatted bench-arc4random data):
SSE MB/s
-----------------------------------------------
arc4random [single-thread] 704.25
arc4random_buf(16) [single-thread] 1018.17
arc4random_buf(32) [single-thread] 1315.27
arc4random_buf(48) [single-thread] 1449.36
arc4random_buf(64) [single-thread] 1511.16
arc4random_buf(80) [single-thread] 1539.48
arc4random_buf(96) [single-thread] 1571.06
arc4random_buf(112) [single-thread] 1596.16
arc4random_buf(128) [single-thread] 1613.48
-----------------------------------------------
AVX2 MB/s
-----------------------------------------------
arc4random [single-thread] 922.61
arc4random_buf(16) [single-thread] 1478.70
arc4random_buf(32) [single-thread] 2241.80
arc4random_buf(48) [single-thread] 2681.28
arc4random_buf(64) [single-thread] 2913.43
arc4random_buf(80) [single-thread] 3009.73
arc4random_buf(96) [single-thread] 3141.16
arc4random_buf(112) [single-thread] 3254.46
arc4random_buf(128) [single-thread] 3305.02
-----------------------------------------------
Checked on x86_64-linux-gnu.
It adds vectorized ChaCha20 implementation based on libgcrypt
cipher/chacha20-amd64-ssse3.S. It replaces the ROTATE_SHUF_2 (which
uses pshufb) by ROTATE2 and thus making the original implementation
SSE2.
As for generic implementation, the last step that XOR with the
input is omited. The final state register clearing is also
omitted.
On a Ryzen 9 5900X it shows the following improvements (using
formatted bench-arc4random data):
GENERIC MB/s
-----------------------------------------------
arc4random [single-thread] 443.11
arc4random_buf(16) [single-thread] 552.27
arc4random_buf(32) [single-thread] 626.86
arc4random_buf(48) [single-thread] 649.81
arc4random_buf(64) [single-thread] 663.95
arc4random_buf(80) [single-thread] 674.78
arc4random_buf(96) [single-thread] 675.17
arc4random_buf(112) [single-thread] 680.69
arc4random_buf(128) [single-thread] 683.20
-----------------------------------------------
SSE MB/s
-----------------------------------------------
arc4random [single-thread] 704.25
arc4random_buf(16) [single-thread] 1018.17
arc4random_buf(32) [single-thread] 1315.27
arc4random_buf(48) [single-thread] 1449.36
arc4random_buf(64) [single-thread] 1511.16
arc4random_buf(80) [single-thread] 1539.48
arc4random_buf(96) [single-thread] 1571.06
arc4random_buf(112) [single-thread] 1596.16
arc4random_buf(128) [single-thread] 1613.48
-----------------------------------------------
Checked on x86_64-linux-gnu.
It adds vectorized ChaCha20 implementation based on libgcrypt
cipher/chacha20-aarch64.S. It is used as default and only
little-endian is supported (BE uses generic code).
As for generic implementation, the last step that XOR with the
input is omited. The final state register clearing is also
omitted.
On a virtualized Linux on Apple M1 it shows the following
improvements (using formatted bench-arc4random data):
GENERIC MB/s
-----------------------------------------------
arc4random [single-thread] 380.89
arc4random_buf(16) [single-thread] 500.73
arc4random_buf(32) [single-thread] 552.61
arc4random_buf(48) [single-thread] 566.82
arc4random_buf(64) [single-thread] 574.01
arc4random_buf(80) [single-thread] 581.02
arc4random_buf(96) [single-thread] 591.19
arc4random_buf(112) [single-thread] 592.29
arc4random_buf(128) [single-thread] 596.43
-----------------------------------------------
OPTIMIZED MB/s
-----------------------------------------------
arc4random [single-thread] 569.60
arc4random_buf(16) [single-thread] 825.78
arc4random_buf(32) [single-thread] 987.03
arc4random_buf(48) [single-thread] 1042.39
arc4random_buf(64) [single-thread] 1075.50
arc4random_buf(80) [single-thread] 1094.68
arc4random_buf(96) [single-thread] 1130.16
arc4random_buf(112) [single-thread] 1129.58
arc4random_buf(128) [single-thread] 1137.91
-----------------------------------------------
Checked on aarch64-linux-gnu.
It shows both throughput (total bytes obtained in the test duration)
and latecy for both arc4random and arc4random_buf with different
sizes.
Checked on x86_64-linux-gnu, aarch64-linux, and powerpc64le-linux-gnu.
The basic tst-arc4random-chacha20.c checks if the output of ChaCha20
implementation matches the reference test vectors from RFC8439.
The tst-arc4random-fork.c check if subprocesses generate distinct
streams of randomness (if fork handling is done correctly).
The tst-arc4random-stats.c is a statistical test to the randomness of
arc4random, arc4random_buf, and arc4random_uniform.
The tst-arc4random-thread.c check if threads generate distinct streams
of randomness (if function are thread-safe).
Checked on x86_64-linux-gnu, aarch64-linux, and powerpc64le-linux-gnu.
Co-authored-by: Florian Weimer <fweimer@redhat.com>
Checked on x86_64-linux-gnu and aarch64-linux-gnu.
The implementation is based on scalar Chacha20 with per-thread cache.
It uses getrandom or /dev/urandom as fallback to get the initial entropy,
and reseeds the internal state on every 16MB of consumed buffer.
To improve performance and lower memory consumption the per-thread cache
is allocated lazily on first arc4random functions call, and if the
memory allocation fails getentropy or /dev/urandom is used as fallback.
The cache is also cleared on thread exit iff it was initialized (so if
arc4random is not called it is not touched).
Although it is lock-free, arc4random is still not async-signal-safe
(the per thread state is not updated atomically).
The ChaCha20 implementation is based on RFC8439 [1], omitting the final
XOR of the keystream with the plaintext because the plaintext is a
stream of zeros. This strategy is similar to what OpenBSD arc4random
does.
The arc4random_uniform is based on previous work by Florian Weimer,
where the algorithm is based on Jérémie Lumbroso paper Optimal Discrete
Uniform Generation from Coin Flips, and Applications (2013) [2], who
credits Donald E. Knuth and Andrew C. Yao, The complexity of nonuniform
random number generation (1976), for solving the general case.
The main advantage of this method is the that the unit of randomness is not
the uniform random variable (uint32_t), but a random bit. It optimizes the
internal buffer sampling by initially consuming a 32-bit random variable
and then sampling byte per byte. Depending of the upper bound requested,
it might lead to better CPU utilization.
Checked on x86_64-linux-gnu, aarch64-linux, and powerpc64le-linux-gnu.
Co-authored-by: Florian Weimer <fweimer@redhat.com>
Reviewed-by: Yann Droneaud <ydroneaud@opteya.com>
[1] https://datatracker.ietf.org/doc/html/rfc8439
[2] https://arxiv.org/pdf/1304.1916.pdf
The locale generation are issues in parallel to try speed locale
generation. The maximum number of jobs are limited to the online
CPU (in hope to not overcommit on environments with lower cores
than tests).
On a Ryzen 9, the test execution improves from ~6.7s to ~1.4s.
Tested-by: Mark Wielaard <mark@klomp.org>
It is prudent not to run too much code after detecting heap
corruption, and __fxprintf is really complex. The line number
and file name do not carry much information, so it is not included
in the error message. (__libc_message only supports %s formatting.)
The function name and assertion should provide some context.
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
This patch updates various miscellaneous files from their upstream
sources (version 2022-05-25).
It is required for loongarch support.
Checked on aarch64-linux-gnu.
Before this the test fails if run in a chroot by a non-root user:
warning: could not become root outside namespace (Operation not permitted)
../sysdeps/unix/sysv/linux/tst-mount.c:36: numeric comparison failure
left: 1 (0x1); from: errno
right: 19 (0x13); from: ENODEV
error: ../sysdeps/unix/sysv/linux/tst-mount.c:39: not true: fd != -1
error: ../sysdeps/unix/sysv/linux/tst-mount.c:46: not true: r != -1
error: ../sysdeps/unix/sysv/linux/tst-mount.c:48: not true: r != -1
../sysdeps/unix/sysv/linux/tst-mount.c:52: numeric comparison failure
left: 1 (0x1); from: errno
right: 9 (0x9); from: EBADF
error: ../sysdeps/unix/sysv/linux/tst-mount.c:55: not true: mfd != -1
../sysdeps/unix/sysv/linux/tst-mount.c:58: numeric comparison failure
left: 1 (0x1); from: errno
right: 2 (0x2); from: ENOENT
error: ../sysdeps/unix/sysv/linux/tst-mount.c:61: not true: r != -1
../sysdeps/unix/sysv/linux/tst-mount.c:65: numeric comparison failure
left: 1 (0x1); from: errno
right: 2 (0x2); from: ENOENT
error: ../sysdeps/unix/sysv/linux/tst-mount.c:68: not true: pfd != -1
error: ../sysdeps/unix/sysv/linux/tst-mount.c:75: not true: fd_tree != -1
../sysdeps/unix/sysv/linux/tst-mount.c:88: numeric comparison failure
left: 1 (0x1); from: errno
right: 38 (0x26); from: ENOSYS
error: 12 test failures
Checking that the test can enter a new mount namespace is more correct
than just checking the return value of support_become_root() as the test
code changes the mount namespace it runs in so running it as root on a
system that does not support mount namespaces should still skip.
Also change the test to remove the unnecessary fork.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
1. Add default ISA level selection in non-multiarch/rtld
implementations.
2. Add ISA level build guards to different implementations.
- I.e strcpy-avx2.S which is ISA level 3 will only build if
compiled ISA level <= 3. Otherwise there is no reason to
include it as we will always use one of the ISA level 4
implementations (strcpy-evex.S).
3. Refactor the ifunc selector and ifunc implementation list to use
the ISA level aware wrapper macros that allow functions below the
compiled ISA level (with a guranteed replacement) to be skipped.
Tested with and without multiarch on x86_64 for ISA levels:
{generic, x86-64-v2, x86-64-v3, x86-64-v4}
And m32 with and without multiarch.
1. Add ISA level build guards to different implementations.
- wcscpy-ssse3.S is used as ISA level 2/3/4.
- wcscpy-generic.c is only used at ISA level 1 and will
only build if compiled with ISA level == 1. Otherwise
there is no reason to include it as we will always use
wcscpy-ssse3.S
2. Refactor the ifunc selector and ifunc implementation list to use
the ISA level aware wrapper macros that allow functions below the
compiled ISA level (with a guranteed replacement) to be skipped.
Tested with and without multiarch on x86_64 for ISA levels:
{generic, x86-64-v2, x86-64-v3, x86-64-v4}
And m32 with and without multiarch.
1. Add default ISA level selection in non-multiarch/rtld
implementations.
2. Add ISA level build guards to different implementations.
- I.e strcmp-avx2.S which is ISA level 3 will only build if
compiled ISA level <= 3. Otherwise there is no reason to
include it as we will always use one of the ISA level 4
implementations (strcmp-evex.S).
3. Refactor the ifunc selector and ifunc implementation list to use
the ISA level aware wrapper macros that allow functions below the
compiled ISA level (with a guranteed replacement) to be skipped.
Tested with and without multiarch on x86_64 for ISA levels:
{generic, x86-64-v2, x86-64-v3, x86-64-v4}
And m32 with and without multiarch.
The fix done b2cd93fce6 does not really
work since macro strification does not expand the sizeof nor the
arithmetic operation.
Checked on x86_64-linux-gnu.
Compilers may not be able to apply asm redirections to functions after
these functions are used for the first time, e.g. clang 13.
Fix [BZ #27087] by applying all long double-related asm redirections
before using functions in bits/stdio.h.
However, as these asm redirections depend on the declarations provided
by libio/bits/stdio2.h, this header was split in 2:
- libio/bits/stdio2-decl.h contains all function declarations;
- libio/bits/stdio2.h remains with the remaining contents, including
redirections.
This also adds the access attribute to __vsnprintf_chk that was missing.
Tested with build-many-glibcs.py.
Reviewed-by: Paul E. Murphy <murphyp@linux.ibm.com>
Starting with commit e070501d12
"Replace __libc_multiple_threads with __libc_single_threaded"
the testcases nptl/tst-cancel-self and
nptl/tst-cancel-self-cancelstate are failing.
This is fixed by only defining SINGLE_THREAD_BY_GLOBAL on s390x,
but not on s390.
Starting with commit 09c76a7409
"Linux: Consolidate {RTLD_}SINGLE_THREAD_P definition",
SINGLE_THREAD_BY_GLOBAL was defined in
sysdeps/unix/sysv/linux/s390/s390-64/sysdep.h.
Lateron the commit 9a973da617
"s390: Consolidate Linux syscall definition" consolidates the sysdep.h files
from s390-32/s390-64 subdirectories. Unfortunately the macro is now always
defined instead of only on s390-64.
As information:
TLS_MULTIPLE_THREADS_IN_TCB is also only defined for s390.
See: sysdeps/s390/nptl/tls.h
wmemcmp isn't used by the dynamic loader so their no need to add an
RTLD stub for it.
Tested with and without multiarch on x86_64 for ISA levels:
{generic, x86-64-v2, x86-64-v3, x86-64-v4}
And m32 with and without multiarch.
This commit doesn't affect libc.so.6, its just housekeeping to prepare
for adding explicit ISA level support.
Tested build on x86_64 and x86_32 with/without multiarch.
This commit doesn't affect libc.so.6, its just housekeeping to prepare
for adding explicit ISA level support.
Tested build on x86_64 and x86_32 with/without multiarch.
This commit doesn't affect libc.so.6, its just housekeeping to prepare
for adding explicit ISA level support.
Tested build on x86_64 and x86_32 with/without multiarch.
This commit doesn't affect libc.so.6, its just housekeeping to prepare
for adding explicit ISA level support.
Tested build on x86_64 and x86_32 with/without multiarch.
This commit doesn't affect libc.so.6, its just housekeeping to prepare
for adding explicit ISA level support.
Tested build on x86_64 and x86_32 with/without multiarch.
This commit doesn't affect libc.so.6, its just housekeeping to prepare
for adding explicit ISA level support.
Tested build on x86_64 and x86_32 with/without multiarch.
This commit doesn't affect libc.so.6, its just housekeeping to prepare
for adding explicit ISA level support.
Tested build on x86_64 and x86_32 with/without multiarch.
This commit doesn't affect libc.so.6, its just housekeeping to prepare
for adding explicit ISA level support.
Tested build on x86_64 and x86_32 with/without multiarch.
This commit doesn't affect libc.so.6, its just housekeeping to prepare
for adding explicit ISA level support.
Tested build on x86_64 and x86_32 with/without multiarch.
This commit doesn't affect libc.so.6, its just housekeeping to prepare
for adding explicit ISA level support.
Tested build on x86_64 and x86_32 with/without multiarch.
This commit doesn't affect libc.so.6, its just housekeeping to prepare
for adding explicit ISA level support.
Because strcmp-sse2.S implements so many functions (more from
avx2/evex/sse42) add a new file 'strcmp-naming.h' to assist in
getting the correct symbol name for all the function across
multiarch/non-multiarch builds.
Tested build on x86_64 and x86_32 with/without multiarch.
The previous macro name can be confusing given that both
`__strcasecmp_l_nonascii` and `__strcasecmp_nonascii` are
functions and we use the `_l` version.
The intrinsics are not available before GCC7 and using standard
operators generates code of equivalent or better quality.
Removed:
_cvtmask64_u64
_kshiftri_mask64
_kand_mask64
Geometric Mean of 5 Runs of Full Benchmark Suite New / Old: 0.958
These functions all have optimized versions:
__strncat_sse2_unaligned, __strncpy_sse2_unaligned, and
stpncpy_sse2_unaligned which are faster than their respective generic
implementations. Since the sse2 versions can run on baseline x86_64,
we should use these as the baseline implementation and can remove the
generic implementations.
Geometric mean of N=20 runs of the entire benchmark suite on:
11th Gen Intel(R) Core(TM) i7-1165G7 @ 2.80GHz (Tigerlake)
__strncat_sse2_unaligned / __strncat_generic: .944
__strncpy_sse2_unaligned / __strncpy_generic: .726
__stpncpy_sse2_unaligned / __stpncpy_generic: .650
Tested build with and without multiarch and full check with multiarch.
gas -mtune= may change NOP generating patterns but -mtune=i686 has no
difference from the default by inspecting .o and .os files.
Note: Clang doesn't support -Wa,-mtune=i686.
Remove redundant strcspn-generic, strpbrk-generic and strspn-generic
from sysdep_routines in sysdeps/x86_64/multiarch/Makefile added by
commit c69f960b01
Author: Noah Goldstein <goldstein.w.n@gmail.com>
Date: Sun Jul 3 21:28:07 2022 -0700
x86: Add support for building str{c|p}{brk|spn} with explicit ISA level
since they have been added to sysdep_routines in sysdeps/x86_64/Makefile.
This change adds tests for the mbrtoc8 and c8rtomb functions adopted for
C++20 via WG21 P0482R6 and for C2X via WG14 N2653, and for the char8_t
typedef adopted for C2X from WG14 N2653.
The tests for mbrtoc8 and c8rtomb specifically exercise conversion to
and from Big5-HKSCS because of special cases that arise with that encoding.
Big5-HKSCS defines some double byte sequences that convert to more than
one Unicode code point. In order to test this, the locale dependencies
for running tests under wcsmbs is expanded to include zh_HK.BIG5-HKSCS.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
This change provides implementations for the mbrtoc8 and c8rtomb
functions adopted for C++20 via WG21 P0482R6 and for C2X via WG14
N2653. It also provides the char8_t typedef from WG14 N2653.
The mbrtoc8 and c8rtomb functions are declared in uchar.h in C2X
mode or when the _GNU_SOURCE macro or C++20 __cpp_char8_t feature
test macro is defined.
The char8_t typedef is declared in uchar.h in C2X mode or when the
_GNU_SOURCE macro is defined and the C++20 __cpp_char8_t feature
test macro is not defined (if __cpp_char8_t is defined, then char8_t
is a builtin type).
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
This patch corrects the Big5-HKSCS converter to preserve the lowest 3 bits of
the mbstate_t __count data member when the converter encounters an incomplete
multibyte character.
This fixes BZ #25744.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
We found that string functions were using AND+ADDP
to find the nibble/syndrome mask but there is an easier
opportunity through `SHRN dst.8b, src.8h, 4` (shift
right every 2 bytes by 4 and narrow to 1 byte) and has
same latency on all SIMD ARMv8 targets as ADDP. There
are also possible gaps for memcmp but that's for
another patch.
We see 10-20% savings for small-mid size cases (<=128)
which are primary cases for general workloads.
Since Linux 4.9, the kernel provides
/proc/sys/user/max_{mnt,pid,user}_namespace as a limitation of number of
namespaces. Some distros (for example, Slint Linux 14.2.1) set them (or
only max_user_namespace) to zero as a "security policy" for disabling
namespaces.
The clone() call will set errno to ENOSPC under such a limitation. We
didn't check ENOSPC in the code so the test will FAIL, and report:
unable to unshare user/fs: No space left on device
This message is, unfortunately, very unhelpful. It leads people to
check the memory or disk space, instead of finding the real issue.
To improve the situation, we should check for ENOSPC and return
UNSUPPORTED as the test result. Also refactor check_for_unshare_hints()
to emit a proper message telling people how to make the test work, if
they really need to run the namespaced tests.
Reported-by: Philippe Delavalade <philippe.delavalade@orange.fr>
URL: https://lists.linuxfromscratch.org/sympa/arc/lfs-support/2022-06/msg00022.html
Signed-off-by: Xi Ruoyao <xry111@xry111.site>
Reviewed-by: DJ Delorie <dj@redhat.com>
1. Refactor files so that all implementations are in the multiarch
directory
- Moved the implementation portion of memcmp sse2 from memcmp.S to
multiarch/memcmp-sse2.S
- The non-multiarch file now only includes one of the
implementations in the multiarch directory based on the compiled
ISA level (only used for non-multiarch builds. Otherwise we go
through the ifunc selector).
2. Add ISA level build guards to different implementations.
- I.e memcmp-avx2-movsb.S which is ISA level 3 will only build if
compiled ISA level <= 3. Otherwise there is no reason to include
it as we will always use one of the ISA level 4
implementations (memcmp-evex-movbe.S).
3. Add new multiarch/rtld-{w}memcmp{eq}.S that just include the
non-multiarch {w}memcmp{eq}.S which will in turn select the best
implementation based on the compiled ISA level.
4. Refactor the ifunc selector and ifunc implementation list to use
the ISA level aware wrapper macros that allow functions below the
compiled ISA level (with a guranteed replacement) to be skipped.
Tested with and without multiarch on x86_64 for ISA levels:
{generic, x86-64-v2, x86-64-v3, x86-64-v4}
And m32 with and without multiarch.
1. Refactor files so that all implementations are in the multiarch
directory
- Moved the implementation portion of memset sse2 from memset.S to
multiarch/memset-sse2.S
- The non-multiarch file now only includes one of the
implementations in the multiarch directory based on the compiled
ISA level (only used for non-multiarch builds. Otherwise we go
through the ifunc selector).
2. Add ISA level build guards to different implementations.
- I.e memset-avx2-unaligned-erms.S which is ISA level 3 will only
build if compiled ISA level <= 3. Otherwise there is no reason
to include it as we will always use one of the ISA level 4
implementations (memset-evex-unaligned-erms.S).
3. Add new multiarch/rtld-memset.S that just include the
non-multiarch memset.S which will in turn select the best
implementation based on the compiled ISA level.
4. Refactor the ifunc selector and ifunc implementation list to use
the ISA level aware wrapper macros that allow functions below the
compiled ISA level (with a guranteed replacement) to be skipped.
Tested with and without multiarch on x86_64 for ISA levels:
{generic, x86-64-v2, x86-64-v3, x86-64-v4}
And m32 with and without multiarch.
1. Refactor files so that all implementations are in the multiarch
directory
- Moved the implementation portion of memmove sse2 from memmove.S
to multiarch/memmove-sse2.S
- The non-multiarch file now only includes one of the
implementations in the multiarch directory based on the compiled
ISA level (only used for non-multiarch builds. Otherwise we go
through the ifunc selector).
2. Add ISA level build guards to different implementations.
- I.e memmove-avx2-unaligned-erms.S which is ISA level 3 will only
build if compiled ISA level <= 3. Otherwise there is no reason
to include it as we will always use one of the ISA level 4
implementations (memmove-evex-unaligned-erms.S).
3. Add new multiarch/rtld-memmove.S that just include the
non-multiarch memmove.S which will in turn select the best
implementation based on the compiled ISA level.
4. Refactor the ifunc selector and ifunc implementation list to use
the ISA level aware wrapper macros that allow functions below the
compiled ISA level (with a guranteed replacement) to be skipped.
Tested with and without multiarch on x86_64 for ISA levels:
{generic, x86-64-v2, x86-64-v3, x86-64-v4}
And m32 with and without multiarch.
isa raising memmove
The changes for these functions are different than the others because
the best implementation (sse4_2) requires the generic
implementation as a fallback to be built as well.
Changes are:
1. Add non-multiarch functions for str{c|p}{brk|spn}.c to statically
select the best implementation based on the configured ISA build
level.
2. Add stubs for str{c|p}{brk|spn}-generic and varshift.c to in the
sysdeps/x86_64 directory so that the the sse4 implementation will
have all of its dependencies for the non-multiarch / rtld build
when ISA level >= 2.
3. Add new multiarch/rtld-strcspn.c that just include the
non-multiarch strcspn.c which will in turn select the best
implementation based on the compiled ISA level.
4. Refactor the ifunc selector and ifunc implementation list to use
the ISA level aware wrapper macros that allow functions below the
compiled ISA level (with a guranteed replacement) to be skipped.
Tested with and without multiarch on x86_64 for ISA levels:
{generic, x86-64-v2, x86-64-v3, x86-64-v4}
And m32 with and without multiarch.
And also fixes the SINGLE_THREAD_P macro for SINGLE_THREAD_BY_GLOBAL,
since header inclusion single-thread.h is in the wrong order, the define
needs to come before including sysdeps/unix/sysdep.h. The macro
is now moved to a per-arch single-threade.h header.
The SINGLE_THREAD_P is used on some more places.
Checked on aarch64-linux-gnu and x86_64-linux-gnu.
It was added on Linux 5.12 (2a1867219c7b27f928e2545782b86daaf9ad50bd)
to allow change the properties of a mount or a mount tree using file
descriptors which the new mount api is based on.
Checked on x86_64-linux-gnu.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
