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461cab1de7
Linux 6.11 has getrandom() in vDSO. It operates on a thread-local opaque state allocated with mmap using flags specified by the vDSO. Multiple states are allocated at once, as many as fit into a page, and these are held in an array of available states to be doled out to each thread upon first use, and recycled when a thread terminates. As these states run low, more are allocated. To make this procedure async-signal-safe, a simple guard is used in the LSB of the opaque state address, falling back to the syscall if there's reentrancy contention. Also, _Fork() is handled by blocking signals on opaque state allocation (so _Fork() always sees a consistent state even if it interrupts a getrandom() call) and by iterating over the thread stack cache on reclaim_stack. Each opaque state will be in the free states list (grnd_alloc.states) or allocated to a running thread. The cancellation is handled by always using GRND_NONBLOCK flags while calling the vDSO, and falling back to the cancellable syscall if the kernel returns EAGAIN (would block). Since getrandom is not defined by POSIX and cancellation is supported as an extension, the cancellation is handled as 'may occur' instead of 'shall occur' [1], meaning that if vDSO does not block (the expected behavior) getrandom will not act as a cancellation entrypoint. It avoids a pthread_testcancel call on the fast path (different than 'shall occur' functions, like sem_wait()). It is currently enabled for x86_64, which is available in Linux 6.11, and aarch64, powerpc32, powerpc64, loongarch64, and s390x, which are available in Linux 6.12. Link: https://pubs.opengroup.org/onlinepubs/9799919799/nframe.html [1] Co-developed-by: Jason A. Donenfeld <Jason@zx2c4.com> Tested-by: Jason A. Donenfeld <Jason@zx2c4.com> # x86_64 Tested-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> # x86_64, aarch64 Tested-by: Xi Ruoyao <xry111@xry111.site> # x86_64, aarch64, loongarch64 Tested-by: Stefan Liebler <stli@linux.ibm.com> # s390x
240 lines
6.9 KiB
C
240 lines
6.9 KiB
C
/* Copyright (C) 2005-2024 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 License as
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published by the Free Software Foundation; either version 2.1 of the
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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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#ifndef _LINUX_AARCH64_SYSDEP_H
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#define _LINUX_AARCH64_SYSDEP_H 1
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#include <sysdeps/unix/sysdep.h>
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#include <sysdeps/aarch64/sysdep.h>
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#include <sysdeps/unix/sysdep.h>
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#include <sysdeps/unix/sysv/linux/sysdep.h>
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/* Defines RTLD_PRIVATE_ERRNO and USE_DL_SYSINFO. */
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#include <dl-sysdep.h>
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#include <tls.h>
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/* In order to get __set_errno() definition in INLINE_SYSCALL. */
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#ifndef __ASSEMBLER__
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#include <errno.h>
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#endif
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/* For Linux we can use the system call table in the header file
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/usr/include/asm/unistd.h
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of the kernel. But these symbols do not follow the SYS_* syntax
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so we have to redefine the `SYS_ify' macro here. */
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#undef SYS_ify
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#define SYS_ify(syscall_name) (__NR_##syscall_name)
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#ifdef __ASSEMBLER__
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/* Linux uses a negative return value to indicate syscall errors,
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unlike most Unices, which use the condition codes' carry flag.
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Since version 2.1 the return value of a system call might be
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negative even if the call succeeded. E.g., the `lseek' system call
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might return a large offset. Therefore we must not anymore test
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for < 0, but test for a real error by making sure the value in R0
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is a real error number. Linus said he will make sure the no syscall
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returns a value in -1 .. -4095 as a valid result so we can safely
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test with -4095. */
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# undef PSEUDO
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# define PSEUDO(name, syscall_name, args) \
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.text; \
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ENTRY (name); \
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DO_CALL (syscall_name, args); \
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cmn x0, #4095; \
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b.cs .Lsyscall_error;
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# undef PSEUDO_END
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# define PSEUDO_END(name) \
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SYSCALL_ERROR_HANDLER \
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END (name)
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# undef PSEUDO_NOERRNO
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# define PSEUDO_NOERRNO(name, syscall_name, args) \
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.text; \
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ENTRY (name); \
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DO_CALL (syscall_name, args);
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# undef PSEUDO_END_NOERRNO
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# define PSEUDO_END_NOERRNO(name) \
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END (name)
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# define ret_NOERRNO ret
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/* The function has to return the error code. */
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# undef PSEUDO_ERRVAL
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# define PSEUDO_ERRVAL(name, syscall_name, args) \
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.text; \
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ENTRY (name) \
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DO_CALL (syscall_name, args); \
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neg x0, x0
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# undef PSEUDO_END_ERRVAL
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# define PSEUDO_END_ERRVAL(name) \
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END (name)
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# define ret_ERRVAL ret
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# if !IS_IN (libc)
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# define SYSCALL_ERROR .Lsyscall_error
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# if RTLD_PRIVATE_ERRNO
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# define SYSCALL_ERROR_HANDLER \
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.Lsyscall_error: \
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adrp x1, C_SYMBOL_NAME(rtld_errno); \
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neg w0, w0; \
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str w0, [x1, :lo12:C_SYMBOL_NAME(rtld_errno)]; \
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mov x0, -1; \
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RET;
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# else
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# define SYSCALL_ERROR_HANDLER \
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.Lsyscall_error: \
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adrp x1, :gottprel:errno; \
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neg w2, w0; \
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ldr PTR_REG(1), [x1, :gottprel_lo12:errno]; \
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mrs x3, tpidr_el0; \
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mov x0, -1; \
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str w2, [x1, x3]; \
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RET;
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# endif
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# else
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# define SYSCALL_ERROR __syscall_error
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# define SYSCALL_ERROR_HANDLER \
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.Lsyscall_error: \
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b __syscall_error;
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# endif
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/* Linux takes system call args in registers:
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syscall number x8
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arg 1 x0
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arg 2 x1
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arg 3 x2
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arg 4 x3
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arg 5 x4
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arg 6 x5
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arg 7 x6
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The compiler is going to form a call by coming here, through PSEUDO, with
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arguments
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syscall number in the DO_CALL macro
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arg 1 x0
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arg 2 x1
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arg 3 x2
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arg 4 x3
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arg 5 x4
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arg 6 x5
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arg 7 x6
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*/
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# undef DO_CALL
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# define DO_CALL(syscall_name, args) \
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mov x8, SYS_ify (syscall_name); \
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svc 0
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#else /* not __ASSEMBLER__ */
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# ifdef __LP64__
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# define VDSO_NAME "LINUX_2.6.39"
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# define VDSO_HASH 123718537
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# else
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# define VDSO_NAME "LINUX_4.9"
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# define VDSO_HASH 61765625
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# endif
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/* List of system calls which are supported as vsyscalls. */
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# define HAVE_CLOCK_GETRES64_VSYSCALL "__kernel_clock_getres"
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# define HAVE_CLOCK_GETTIME64_VSYSCALL "__kernel_clock_gettime"
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# define HAVE_GETTIMEOFDAY_VSYSCALL "__kernel_gettimeofday"
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# define HAVE_GETRANDOM_VSYSCALL "__kernel_getrandom"
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# define HAVE_CLONE3_WRAPPER 1
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# undef INTERNAL_SYSCALL_RAW
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# define INTERNAL_SYSCALL_RAW(name, nr, args...) \
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({ long _sys_result; \
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{ \
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LOAD_ARGS_##nr (args) \
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register long _x8 asm ("x8") = (name); \
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asm volatile ("svc 0 // syscall " # name \
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: "=r" (_x0) : "r"(_x8) ASM_ARGS_##nr : "memory"); \
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_sys_result = _x0; \
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} \
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_sys_result; })
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# undef INTERNAL_SYSCALL
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# define INTERNAL_SYSCALL(name, nr, args...) \
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INTERNAL_SYSCALL_RAW(SYS_ify(name), nr, args)
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# undef INTERNAL_SYSCALL_AARCH64
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# define INTERNAL_SYSCALL_AARCH64(name, nr, args...) \
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INTERNAL_SYSCALL_RAW(__ARM_NR_##name, nr, args)
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# define LOAD_ARGS_0() \
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register long _x0 asm ("x0");
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# define LOAD_ARGS_1(x0) \
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long _x0tmp = (long) (x0); \
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LOAD_ARGS_0 () \
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_x0 = _x0tmp;
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# define LOAD_ARGS_2(x0, x1) \
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long _x1tmp = (long) (x1); \
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LOAD_ARGS_1 (x0) \
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register long _x1 asm ("x1") = _x1tmp;
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# define LOAD_ARGS_3(x0, x1, x2) \
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long _x2tmp = (long) (x2); \
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LOAD_ARGS_2 (x0, x1) \
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register long _x2 asm ("x2") = _x2tmp;
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# define LOAD_ARGS_4(x0, x1, x2, x3) \
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long _x3tmp = (long) (x3); \
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LOAD_ARGS_3 (x0, x1, x2) \
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register long _x3 asm ("x3") = _x3tmp;
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# define LOAD_ARGS_5(x0, x1, x2, x3, x4) \
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long _x4tmp = (long) (x4); \
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LOAD_ARGS_4 (x0, x1, x2, x3) \
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register long _x4 asm ("x4") = _x4tmp;
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# define LOAD_ARGS_6(x0, x1, x2, x3, x4, x5) \
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long _x5tmp = (long) (x5); \
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LOAD_ARGS_5 (x0, x1, x2, x3, x4) \
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register long _x5 asm ("x5") = _x5tmp;
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# define LOAD_ARGS_7(x0, x1, x2, x3, x4, x5, x6)\
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long _x6tmp = (long) (x6); \
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LOAD_ARGS_6 (x0, x1, x2, x3, x4, x5) \
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register long _x6 asm ("x6") = _x6tmp;
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# define ASM_ARGS_0
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# define ASM_ARGS_1 , "r" (_x0)
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# define ASM_ARGS_2 ASM_ARGS_1, "r" (_x1)
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# define ASM_ARGS_3 ASM_ARGS_2, "r" (_x2)
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# define ASM_ARGS_4 ASM_ARGS_3, "r" (_x3)
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# define ASM_ARGS_5 ASM_ARGS_4, "r" (_x4)
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# define ASM_ARGS_6 ASM_ARGS_5, "r" (_x5)
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# define ASM_ARGS_7 ASM_ARGS_6, "r" (_x6)
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# undef INTERNAL_SYSCALL_NCS
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# define INTERNAL_SYSCALL_NCS(number, nr, args...) \
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INTERNAL_SYSCALL_RAW (number, nr, args)
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#undef HAVE_INTERNAL_BRK_ADDR_SYMBOL
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#define HAVE_INTERNAL_BRK_ADDR_SYMBOL 1
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#endif /* __ASSEMBLER__ */
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#endif /* linux/aarch64/sysdep.h */
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