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x86: Remove arch-specific low level lock implementation
This patch removes the arch-specific x86 assembly implementation for low level locking and consolidate both 64 bits and 32 bits in a single implementation. Different than other architectures, x86 lll_trylock, lll_lock, and lll_unlock implements a single-thread optimization to avoid atomic operation, using cmpxchgl instead. This patch implements by using the new single-thread.h definitions in a generic way, although using the previous semantic. The lll_cond_trylock, lll_cond_lock, and lll_timedlock just use atomic operations plus calls to lll_lock_wait*. For __lll_lock_wait_private and __lll_lock_wait the generic implemtation there is no indication that assembly implementation is required performance-wise. Checked on x86_64-linux-gnu and i686-linux-gnu. * sysdeps/nptl/lowlevellock.h (__lll_trylock): New macro. (lll_trylock): Call __lll_trylock. * sysdeps/unix/sysv/linux/i386/libc-lowlevellock.S: Remove file. * sysdeps/unix/sysv/linux/i386/lll_timedlock_wait.c: Likewise. * sysdeps/unix/sysv/linux/i386/lowlevellock.S: Likewise. * sysdeps/unix/sysv/linux/i386/lowlevellock.h: Likewise. * sysdeps/unix/sysv/linux/x86_64/libc-lowlevellock.S: Likewise. * sysdeps/unix/sysv/linux/x86_64/lll_timedlock_wait.c: Likewise. * sysdeps/unix/sysv/linux/x86_64/lowlevellock.S: Likewise. * sysdeps/unix/sysv/linux/x86_64/lowlevellock.h: Likewise. * sysdeps/unix/sysv/linux/x86/lowlevellock.h: New file. * sysdeps/unix/sysv/linux/x86_64/cancellation.S: Include lowlevellock-futex.h.
This commit is contained in:
Adhemerval Zanella
110
sysdeps/unix/sysv/linux/x86/lowlevellock.h
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110
sysdeps/unix/sysv/linux/x86/lowlevellock.h
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/* Low-level lock implementation, x86 version.
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Copyright (C) 2019 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#ifndef _X86_64_LOWLEVELLOCK_H
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#define _X86_64_LOWLEVELLOCK_H 1
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#ifndef __ASSEMBLER__
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#include <sysdeps/nptl/lowlevellock.h>
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#include <single-thread.h>
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/* The lll_trylock, lll_lock, and lll_unlock implements a single-thread
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optimization using the cmpxchgl instruction. It checks if the process
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is single thread and avoid a more expensive atomic instruction. */
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/* The single-thread optimization only works for libc itself, we need
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atomicity for libpthread in case of shared futexes. */
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#if !IS_IN(libc)
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# define is_single_thread 0
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#else
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# define is_single_thread SINGLE_THREAD_P
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#endif
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/* In the __lllc_as we simply return the value in %eax after the cmpxchg
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instruction. In case the operation succeeded this value is zero. In case
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the operation failed, the cmpxchg instruction has loaded the current value
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of the memory work which is guaranteed to be nonzero. */
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static inline int
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__attribute__ ((always_inline))
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__lll_cas_lock (int *futex)
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{
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int ret;
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asm volatile ("cmpxchgl %2, %1"
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: "=a" (ret), "=m" (*futex)
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: "r" (1), "m" (*futex), "0" (0)
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: "memory");
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return ret;
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}
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#undef lll_trylock
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#define lll_trylock(lock) \
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({ \
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int __ret; \
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if (is_single_thread) \
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__ret = __lll_cas_lock (&(lock)); \
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else \
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__ret = __lll_trylock (&(lock)); \
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__ret; \
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})
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#undef lll_lock
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#define lll_lock(lock, private) \
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((void) \
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({ \
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if (is_single_thread) \
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__lll_cas_lock (&(lock)); \
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else \
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__lll_lock (&(lock), private); \
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}))
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#undef lll_unlock
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#define lll_unlock(lock, private) \
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((void) \
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({ \
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if (is_single_thread) \
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(lock)--; \
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else \
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__lll_unlock (&(lock), private); \
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}))
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extern int __lll_timedlock_elision (int *futex, short *adapt_count,
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const struct timespec *timeout,
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int private) attribute_hidden;
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#define lll_timedlock_elision(futex, adapt_count, timeout, private) \
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__lll_timedlock_elision(&(futex), &(adapt_count), timeout, private)
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extern int __lll_lock_elision (int *futex, short *adapt_count, int private)
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attribute_hidden;
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extern int __lll_unlock_elision (int *lock, int private)
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attribute_hidden;
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extern int __lll_trylock_elision (int *lock, short *adapt_count)
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attribute_hidden;
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#define lll_lock_elision(futex, adapt_count, private) \
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__lll_lock_elision (&(futex), &(adapt_count), private)
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#define lll_unlock_elision(futex, adapt_count, private) \
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__lll_unlock_elision (&(futex), private)
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#define lll_trylock_elision(futex, adapt_count) \
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__lll_trylock_elision (&(futex), &(adapt_count))
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#endif /* !__ASSEMBLER__ */
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#endif /* lowlevellock.h */
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