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RISC-V: Task implementation
This patch contains the implementation of tasks on RISC-V, most of which is involved in task switching. Signed-off-by: Palmer Dabbelt <[email protected]>
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‎arch/riscv/include/asm/asm-offsets.h‎

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#include <generated/asm-offsets.h>

‎arch/riscv/include/asm/current.h‎

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/*
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* Based on arm/arm64/include/asm/current.h
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*
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* Copyright (C) 2016 ARM
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* Copyright (C) 2017 SiFive
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation, version 2.
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*
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* This program 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
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* GNU General Public License for more details.
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*/
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#ifndef __ASM_CURRENT_H
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#define __ASM_CURRENT_H
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#include <linux/bug.h>
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#include <linux/compiler.h>
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#ifndef __ASSEMBLY__
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struct task_struct;
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/*
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* This only works because "struct thread_info" is at offset 0 from "struct
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* task_struct". This constraint seems to be necessary on other architectures
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* as well, but __switch_to enforces it. We can't check TASK_TI here because
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* <asm/asm-offsets.h> includes this, and I can't get the definition of "struct
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* task_struct" here due to some header ordering problems.
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*/
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static __always_inline struct task_struct *get_current(void)
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{
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register struct task_struct *tp __asm__("tp");
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return tp;
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}
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#define current get_current()
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#endif /* __ASSEMBLY__ */
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#endif /* __ASM_CURRENT_H */

‎arch/riscv/include/asm/kprobes.h‎

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/*
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* Copied from arch/arm64/include/asm/kprobes.h
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*
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* Copyright (C) 2013 Linaro Limited
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* Copyright (C) 2017 SiFive
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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* This program 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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* General Public License for more details.
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*/
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#ifndef _RISCV_KPROBES_H
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#define _RISCV_KPROBES_H
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#include <asm-generic/kprobes.h>
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#endif /* _RISCV_KPROBES_H */

‎arch/riscv/include/asm/processor.h‎

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/*
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* Copyright (C) 2012 Regents of the University of California
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation, version 2.
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*
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* This program 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
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* GNU General Public License for more details.
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*/
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#ifndef _ASM_RISCV_PROCESSOR_H
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#define _ASM_RISCV_PROCESSOR_H
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#include <linux/const.h>
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#include <asm/ptrace.h>
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/*
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* This decides where the kernel will search for a free chunk of vm
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* space during mmap's.
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*/
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#define TASK_UNMAPPED_BASE PAGE_ALIGN(TASK_SIZE >> 1)
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#define STACK_TOP TASK_SIZE
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#define STACK_TOP_MAX STACK_TOP
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#define STACK_ALIGN 16
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#ifndef __ASSEMBLY__
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struct task_struct;
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struct pt_regs;
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/*
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* Default implementation of macro that returns current
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* instruction pointer ("program counter").
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*/
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#define current_text_addr() ({ __label__ _l; _l: &&_l; })
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/* CPU-specific state of a task */
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struct thread_struct {
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/* Callee-saved registers */
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unsigned long ra;
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unsigned long sp; /* Kernel mode stack */
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unsigned long s[12]; /* s[0]: frame pointer */
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struct __riscv_d_ext_state fstate;
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};
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#define INIT_THREAD { \
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.sp = sizeof(init_stack) + (long)&init_stack, \
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}
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#define task_pt_regs(tsk) \
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((struct pt_regs *)(task_stack_page(tsk) + THREAD_SIZE \
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- ALIGN(sizeof(struct pt_regs), STACK_ALIGN)))
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#define KSTK_EIP(tsk) (task_pt_regs(tsk)->sepc)
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#define KSTK_ESP(tsk) (task_pt_regs(tsk)->sp)
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/* Do necessary setup to start up a newly executed thread. */
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extern void start_thread(struct pt_regs *regs,
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unsigned long pc, unsigned long sp);
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/* Free all resources held by a thread. */
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static inline void release_thread(struct task_struct *dead_task)
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{
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}
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extern unsigned long get_wchan(struct task_struct *p);
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static inline void cpu_relax(void)
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{
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#ifdef __riscv_muldiv
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int dummy;
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/* In lieu of a halt instruction, induce a long-latency stall. */
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__asm__ __volatile__ ("div %0, %0, zero" : "=r" (dummy));
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#endif
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barrier();
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}
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static inline void wait_for_interrupt(void)
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{
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__asm__ __volatile__ ("wfi");
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}
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struct device_node;
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extern int riscv_of_processor_hart(struct device_node *node);
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extern void riscv_fill_hwcap(void);
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#endif /* __ASSEMBLY__ */
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#endif /* _ASM_RISCV_PROCESSOR_H */

‎arch/riscv/include/asm/switch_to.h‎

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/*
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* Copyright (C) 2012 Regents of the University of California
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation, version 2.
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*
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* This program 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
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* GNU General Public License for more details.
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*/
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#ifndef _ASM_RISCV_SWITCH_TO_H
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#define _ASM_RISCV_SWITCH_TO_H
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#include <asm/processor.h>
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#include <asm/ptrace.h>
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#include <asm/csr.h>
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extern void __fstate_save(struct task_struct *save_to);
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extern void __fstate_restore(struct task_struct *restore_from);
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static inline void __fstate_clean(struct pt_regs *regs)
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{
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regs->sstatus |= (regs->sstatus & ~(SR_FS)) | SR_FS_CLEAN;
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}
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static inline void fstate_save(struct task_struct *task,
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struct pt_regs *regs)
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{
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if ((regs->sstatus & SR_FS) == SR_FS_DIRTY) {
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__fstate_save(task);
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__fstate_clean(regs);
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}
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}
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static inline void fstate_restore(struct task_struct *task,
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struct pt_regs *regs)
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{
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if ((regs->sstatus & SR_FS) != SR_FS_OFF) {
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__fstate_restore(task);
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__fstate_clean(regs);
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}
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}
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static inline void __switch_to_aux(struct task_struct *prev,
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struct task_struct *next)
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{
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struct pt_regs *regs;
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regs = task_pt_regs(prev);
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if (unlikely(regs->sstatus & SR_SD))
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fstate_save(prev, regs);
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fstate_restore(next, task_pt_regs(next));
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}
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extern struct task_struct *__switch_to(struct task_struct *,
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struct task_struct *);
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#define switch_to(prev, next, last) \
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do { \
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struct task_struct *__prev = (prev); \
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struct task_struct *__next = (next); \
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__switch_to_aux(__prev, __next); \
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((last) = __switch_to(__prev, __next)); \
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} while (0)
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#endif /* _ASM_RISCV_SWITCH_TO_H */

‎arch/riscv/include/asm/thread_info.h‎

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/*
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* Copyright (C) 2009 Chen Liqin <[email protected]>
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* Copyright (C) 2012 Regents of the University of California
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* Copyright (C) 2017 SiFive
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation, version 2.
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*
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* This program 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
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* GNU General Public License for more details.
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*/
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#ifndef _ASM_RISCV_THREAD_INFO_H
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#define _ASM_RISCV_THREAD_INFO_H
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#include <asm/page.h>
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#include <linux/const.h>
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/* thread information allocation */
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#define THREAD_SIZE_ORDER (1)
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#define THREAD_SIZE (PAGE_SIZE << THREAD_SIZE_ORDER)
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#ifndef __ASSEMBLY__
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#include <asm/processor.h>
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#include <asm/csr.h>
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typedef unsigned long mm_segment_t;
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/*
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* low level task data that entry.S needs immediate access to
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* - this struct should fit entirely inside of one cache line
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* - if the members of this struct changes, the assembly constants
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* in asm-offsets.c must be updated accordingly
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* - thread_info is included in task_struct at an offset of 0. This means that
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* tp points to both thread_info and task_struct.
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*/
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struct thread_info {
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unsigned long flags; /* low level flags */
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int preempt_count; /* 0=>preemptible, <0=>BUG */
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mm_segment_t addr_limit;
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/*
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* These stack pointers are overwritten on every system call or
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* exception. SP is also saved to the stack it can be recovered when
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* overwritten.
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*/
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long kernel_sp; /* Kernel stack pointer */
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long user_sp; /* User stack pointer */
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int cpu;
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};
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/*
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* macros/functions for gaining access to the thread information structure
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*
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* preempt_count needs to be 1 initially, until the scheduler is functional.
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*/
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#define INIT_THREAD_INFO(tsk) \
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{ \
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.flags = 0, \
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.preempt_count = INIT_PREEMPT_COUNT, \
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.addr_limit = KERNEL_DS, \
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}
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#define init_stack (init_thread_union.stack)
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#endif /* !__ASSEMBLY__ */
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/*
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* thread information flags
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* - these are process state flags that various assembly files may need to
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* access
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* - pending work-to-be-done flags are in lowest half-word
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* - other flags in upper half-word(s)
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*/
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#define TIF_SYSCALL_TRACE 0 /* syscall trace active */
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#define TIF_NOTIFY_RESUME 1 /* callback before returning to user */
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#define TIF_SIGPENDING 2 /* signal pending */
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#define TIF_NEED_RESCHED 3 /* rescheduling necessary */
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#define TIF_RESTORE_SIGMASK 4 /* restore signal mask in do_signal() */
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#define TIF_MEMDIE 5 /* is terminating due to OOM killer */
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#define TIF_SYSCALL_TRACEPOINT 6 /* syscall tracepoint instrumentation */
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#define _TIF_SYSCALL_TRACE (1 << TIF_SYSCALL_TRACE)
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#define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME)
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#define _TIF_SIGPENDING (1 << TIF_SIGPENDING)
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#define _TIF_NEED_RESCHED (1 << TIF_NEED_RESCHED)
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#define _TIF_WORK_MASK \
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(_TIF_NOTIFY_RESUME | _TIF_SIGPENDING | _TIF_NEED_RESCHED)
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#endif /* _ASM_RISCV_THREAD_INFO_H */

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