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/* Atomic operations. ARM/Linux version.
Copyright (C) 2002-2024 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
<https://www.gnu.org/licenses/>. */
#include <stdint.h>
/* If the compiler doesn't provide a primitive, we'll use this macro
to get assistance from the kernel. */
#ifdef __thumb2__
# define __arm_assisted_full_barrier() \
__asm__ __volatile__ \
("movw\tip, #0x0fa0\n\t" \
"movt\tip, #0xffff\n\t" \
"blx\tip" \
: : : "ip", "lr", "cc", "memory");
#else
# define __arm_assisted_full_barrier() \
__asm__ __volatile__ \
("mov\tip, #0xffff0fff\n\t" \
"mov\tlr, pc\n\t" \
"add\tpc, ip, #(0xffff0fa0 - 0xffff0fff)" \
: : : "ip", "lr", "cc", "memory");
#endif
/* Atomic compare and exchange. This sequence relies on the kernel to
provide a compare and exchange operation which is atomic on the
current architecture, either via cleverness on pre-ARMv6 or via
ldrex / strex on ARMv6.
It doesn't matter what register is used for a_oldval2, but we must
specify one to work around GCC PR rtl-optimization/21223. Otherwise
it may cause a_oldval or a_tmp to be moved to a different register.
We use the union trick rather than simply using __typeof (...) in the
declarations of A_OLDVAL et al because when NEWVAL or OLDVAL is of the
form *PTR and PTR has a 'volatile ... *' type, then __typeof (*PTR) has
a 'volatile ...' type and this triggers -Wvolatile-register-var to
complain about 'register volatile ... asm ("reg")'.
We use the same union trick in the declaration of A_PTR because when
MEM is of the from *PTR and PTR has a 'const ... *' type, then __typeof
(*PTR) has a 'const ...' type and this enables the compiler to substitute
the variable with its initializer in asm statements, which may cause the
corresponding operand to appear in a different register. */
#ifdef __thumb2__
/* Thumb-2 has ldrex/strex. However it does not have barrier instructions,
so we still need to use the kernel helper. */
# define __arm_assisted_compare_and_exchange_val_32_acq(mem, newval, oldval) \
({ union { __typeof (mem) a; uint32_t v; } mem_arg = { .a = (mem) }; \
union { __typeof (oldval) a; uint32_t v; } oldval_arg = { .a = (oldval) };\
union { __typeof (newval) a; uint32_t v; } newval_arg = { .a = (newval) };\
register uint32_t a_oldval asm ("r0"); \
register uint32_t a_newval asm ("r1") = newval_arg.v; \
register uint32_t a_ptr asm ("r2") = mem_arg.v; \
register uint32_t a_tmp asm ("r3"); \
register uint32_t a_oldval2 asm ("r4") = oldval_arg.v; \
__asm__ __volatile__ \
("0:\tldr\t%[tmp],[%[ptr]]\n\t" \
"cmp\t%[tmp], %[old2]\n\t" \
"bne\t1f\n\t" \
"mov\t%[old], %[old2]\n\t" \
"movw\t%[tmp], #0x0fc0\n\t" \
"movt\t%[tmp], #0xffff\n\t" \
"blx\t%[tmp]\n\t" \
"bcc\t0b\n\t" \
"mov\t%[tmp], %[old2]\n\t" \
"1:" \
: [old] "=&r" (a_oldval), [tmp] "=&r" (a_tmp) \
: [new] "r" (a_newval), [ptr] "r" (a_ptr), \
[old2] "r" (a_oldval2) \
: "ip", "lr", "cc", "memory"); \
(__typeof (oldval)) a_tmp; })
#else
# define __arm_assisted_compare_and_exchange_val_32_acq(mem, newval, oldval) \
({ union { __typeof (mem) a; uint32_t v; } mem_arg = { .a = (mem) }; \
union { __typeof (oldval) a; uint32_t v; } oldval_arg = { .a = (oldval) };\
union { __typeof (newval) a; uint32_t v; } newval_arg = { .a = (newval) };\
register uint32_t a_oldval asm ("r0"); \
register uint32_t a_newval asm ("r1") = newval_arg.v; \
register uint32_t a_ptr asm ("r2") = mem_arg.v; \
register uint32_t a_tmp asm ("r3"); \
register uint32_t a_oldval2 asm ("r4") = oldval_arg.v; \
__asm__ __volatile__ \
("0:\tldr\t%[tmp],[%[ptr]]\n\t" \
"cmp\t%[tmp], %[old2]\n\t" \
"bne\t1f\n\t" \
"mov\t%[old], %[old2]\n\t" \
"mov\t%[tmp], #0xffff0fff\n\t" \
"mov\tlr, pc\n\t" \
"add\tpc, %[tmp], #(0xffff0fc0 - 0xffff0fff)\n\t" \
"bcc\t0b\n\t" \
"mov\t%[tmp], %[old2]\n\t" \
"1:" \
: [old] "=&r" (a_oldval), [tmp] "=&r" (a_tmp) \
: [new] "r" (a_newval), [ptr] "r" (a_ptr), \
[old2] "r" (a_oldval2) \
: "ip", "lr", "cc", "memory"); \
(__typeof (oldval)) a_tmp; })
#endif
#include <sysdeps/arm/atomic-machine.h>
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