653c12c7d8
Save a jmp on the lock path coming from an initial failure in pthread_spin_lock.S. This costs 4-bytes of code but since the function still fits in the same number of 16-byte blocks (default function alignment) it does not have affect on the total binary size of libc.so (unchanged after this commit). pthread_spin_trylock was using a CAS when a simple xchg works which is often more expensive. Full check passes on x86-64.
46 lines
1.5 KiB
ArmAsm
46 lines
1.5 KiB
ArmAsm
/* Copyright (C) 2002-2022 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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<https://www.gnu.org/licenses/>. */
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#include <sysdep.h>
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#include <errno.h>
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#include <shlib-compat.h>
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ENTRY(__pthread_spin_trylock)
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xorl %ecx, %ecx
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/* xchg has implicit LOCK prefix. */
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xchgl %ecx, (%rdi)
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/* Branch on result. Expectation is the use of trylock will be
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branching on success/failure so this branch can be used to
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to predict the coming branch. It has the benefit of
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breaking the likely expensive memory dependency on (%rdi). */
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cmpl $1, %ecx
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jnz 1f
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xorl %eax, %eax
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ret
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1:
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movl $EBUSY, %eax
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ret
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END(__pthread_spin_trylock)
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versioned_symbol (libc, __pthread_spin_trylock, pthread_spin_trylock,
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GLIBC_2_34)
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#if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_2, GLIBC_2_34)
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compat_symbol (libpthread, __pthread_spin_trylock, pthread_spin_trylock,
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GLIBC_2_2)
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#endif
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