Minki/linux
1
0
Fork 1
mirror of https://github.com/torvalds/linux.git synced 2024-11-27 06:31:52 +00:00
Code Issues Packages Projects Releases Wiki Activity

RISC-V: Task implementation

Browse Source 
This patch contains the implementation of tasks on RISC-V, most of which
is involved in task switching.

Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>
This commit is contained in:
Palmer Dabbelt 2017-07-10 18:04:30 -07:00
parent 2129a235c0
commit 7db91e57a0
9 changed files with 1243 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/riscv/include/asm/asm-offsets.h Normal file
View File

@ -0,0 +1 @@
#include <generated/asm-offsets.h>

45
arch/riscv/include/asm/current.h Normal file
View File

@ -0,0 +1,45 @@
/*
* Based on arm/arm64/include/asm/current.h
*
* Copyright (C) 2016 ARM
* Copyright (C) 2017 SiFive
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation, version 2.
*
* This program 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 General Public License for more details.
*/
#ifndef __ASM_CURRENT_H
#define __ASM_CURRENT_H
#include <linux/bug.h>
#include <linux/compiler.h>
#ifndef __ASSEMBLY__
struct task_struct;
/*
* This only works because "struct thread_info" is at offset 0 from "struct
* task_struct". This constraint seems to be necessary on other architectures
* as well, but __switch_to enforces it. We can't check TASK_TI here because
* <asm/asm-offsets.h> includes this, and I can't get the definition of "struct
* task_struct" here due to some header ordering problems.
*/
static __always_inline struct task_struct *get_current(void)
{
register struct task_struct *tp __asm__("tp");
return tp;
}
#define current get_current()
#endif /* __ASSEMBLY__ */
#endif /* __ASM_CURRENT_H */

22
arch/riscv/include/asm/kprobes.h Normal file
View File

@ -0,0 +1,22 @@
/*
* Copied from arch/arm64/include/asm/kprobes.h
*
* Copyright (C) 2013 Linaro Limited
* Copyright (C) 2017 SiFive
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* This program 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
* General Public License for more details.
*/
#ifndef _RISCV_KPROBES_H
#define _RISCV_KPROBES_H
#include <asm-generic/kprobes.h>
#endif /* _RISCV_KPROBES_H */

97
arch/riscv/include/asm/processor.h Normal file
View File

@ -0,0 +1,97 @@
/*
* Copyright (C) 2012 Regents of the University of California
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation, version 2.
*
* This program 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 General Public License for more details.
*/
#ifndef _ASM_RISCV_PROCESSOR_H
#define _ASM_RISCV_PROCESSOR_H
#include <linux/const.h>
#include <asm/ptrace.h>
/*
* This decides where the kernel will search for a free chunk of vm
* space during mmap's.
*/
#define TASK_UNMAPPED_BASE PAGE_ALIGN(TASK_SIZE >> 1)
#define STACK_TOP TASK_SIZE
#define STACK_TOP_MAX STACK_TOP
#define STACK_ALIGN 16
#ifndef __ASSEMBLY__
struct task_struct;
struct pt_regs;
/*
* Default implementation of macro that returns current
* instruction pointer ("program counter").
*/
#define current_text_addr() ({ __label__ _l; _l: &&_l; })
/* CPU-specific state of a task */
struct thread_struct {
/* Callee-saved registers */
unsigned long ra;
unsigned long sp; /* Kernel mode stack */
unsigned long s[12]; /* s[0]: frame pointer */
struct __riscv_d_ext_state fstate;
};
#define INIT_THREAD { \
.sp = sizeof(init_stack) + (long)&init_stack, \
}
#define task_pt_regs(tsk) \
((struct pt_regs *)(task_stack_page(tsk) + THREAD_SIZE \
- ALIGN(sizeof(struct pt_regs), STACK_ALIGN)))
#define KSTK_EIP(tsk) (task_pt_regs(tsk)->sepc)
#define KSTK_ESP(tsk) (task_pt_regs(tsk)->sp)
/* Do necessary setup to start up a newly executed thread. */
extern void start_thread(struct pt_regs *regs,
unsigned long pc, unsigned long sp);
/* Free all resources held by a thread. */
static inline void release_thread(struct task_struct *dead_task)
{
}
extern unsigned long get_wchan(struct task_struct *p);
static inline void cpu_relax(void)
{
#ifdef __riscv_muldiv
int dummy;
/* In lieu of a halt instruction, induce a long-latency stall. */
__asm__ __volatile__ ("div %0, %0, zero" : "=r" (dummy));
#endif
barrier();
}
static inline void wait_for_interrupt(void)
{
__asm__ __volatile__ ("wfi");
}
struct device_node;
extern int riscv_of_processor_hart(struct device_node *node);
extern void riscv_fill_hwcap(void);
#endif /* __ASSEMBLY__ */
#endif /* _ASM_RISCV_PROCESSOR_H */

69
arch/riscv/include/asm/switch_to.h Normal file
View File

@ -0,0 +1,69 @@
/*
* Copyright (C) 2012 Regents of the University of California
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation, version 2.
*
* This program 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 General Public License for more details.
*/
#ifndef _ASM_RISCV_SWITCH_TO_H
#define _ASM_RISCV_SWITCH_TO_H
#include <asm/processor.h>
#include <asm/ptrace.h>
#include <asm/csr.h>
extern void __fstate_save(struct task_struct *save_to);
extern void __fstate_restore(struct task_struct *restore_from);
static inline void __fstate_clean(struct pt_regs *regs)
{
regs->sstatus |= (regs->sstatus & ~(SR_FS)) | SR_FS_CLEAN;
}
static inline void fstate_save(struct task_struct *task,
struct pt_regs *regs)
{
if ((regs->sstatus & SR_FS) == SR_FS_DIRTY) {
__fstate_save(task);
__fstate_clean(regs);
}
}
static inline void fstate_restore(struct task_struct *task,
struct pt_regs *regs)
{
if ((regs->sstatus & SR_FS) != SR_FS_OFF) {
__fstate_restore(task);
__fstate_clean(regs);
}
}
static inline void __switch_to_aux(struct task_struct *prev,
struct task_struct *next)
{
struct pt_regs *regs;
regs = task_pt_regs(prev);
if (unlikely(regs->sstatus & SR_SD))
fstate_save(prev, regs);
fstate_restore(next, task_pt_regs(next));
}
extern struct task_struct *__switch_to(struct task_struct *,
struct task_struct *);
#define switch_to(prev, next, last) \
do { \
struct task_struct *__prev = (prev); \
struct task_struct *__next = (next); \
__switch_to_aux(__prev, __next); \
((last) = __switch_to(__prev, __next)); \
} while (0)
#endif /* _ASM_RISCV_SWITCH_TO_H */

94
arch/riscv/include/asm/thread_info.h Normal file
View File

@ -0,0 +1,94 @@
/*
* Copyright (C) 2009 Chen Liqin <liqin.chen@sunplusct.com>
* Copyright (C) 2012 Regents of the University of California
* Copyright (C) 2017 SiFive
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation, version 2.
*
* This program 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 General Public License for more details.
*/
#ifndef _ASM_RISCV_THREAD_INFO_H
#define _ASM_RISCV_THREAD_INFO_H
#include <asm/page.h>
#include <linux/const.h>
/* thread information allocation */
#define THREAD_SIZE_ORDER (1)
#define THREAD_SIZE (PAGE_SIZE << THREAD_SIZE_ORDER)
#ifndef __ASSEMBLY__
#include <asm/processor.h>
#include <asm/csr.h>
typedef unsigned long mm_segment_t;
/*
* low level task data that entry.S needs immediate access to
* - this struct should fit entirely inside of one cache line
* - if the members of this struct changes, the assembly constants
* in asm-offsets.c must be updated accordingly
* - thread_info is included in task_struct at an offset of 0. This means that
* tp points to both thread_info and task_struct.
*/
struct thread_info {
unsigned long flags; /* low level flags */
int preempt_count; /* 0=>preemptible, <0=>BUG */
mm_segment_t addr_limit;
/*
* These stack pointers are overwritten on every system call or
* exception. SP is also saved to the stack it can be recovered when
* overwritten.
*/
long kernel_sp; /* Kernel stack pointer */
long user_sp; /* User stack pointer */
int cpu;
};
/*
* macros/functions for gaining access to the thread information structure
*
* preempt_count needs to be 1 initially, until the scheduler is functional.
*/
#define INIT_THREAD_INFO(tsk) \
{ \
.flags = 0, \
.preempt_count = INIT_PREEMPT_COUNT, \
.addr_limit = KERNEL_DS, \
}
#define init_stack (init_thread_union.stack)
#endif /* !__ASSEMBLY__ */
/*
* thread information flags
* - these are process state flags that various assembly files may need to
* access
* - pending work-to-be-done flags are in lowest half-word
* - other flags in upper half-word(s)
*/
#define TIF_SYSCALL_TRACE 0 /* syscall trace active */
#define TIF_NOTIFY_RESUME 1 /* callback before returning to user */
#define TIF_SIGPENDING 2 /* signal pending */
#define TIF_NEED_RESCHED 3 /* rescheduling necessary */
#define TIF_RESTORE_SIGMASK 4 /* restore signal mask in do_signal() */
#define TIF_MEMDIE 5 /* is terminating due to OOM killer */
#define TIF_SYSCALL_TRACEPOINT 6 /* syscall tracepoint instrumentation */
#define _TIF_SYSCALL_TRACE (1 << TIF_SYSCALL_TRACE)
#define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME)
#define _TIF_SIGPENDING (1 << TIF_SIGPENDING)
#define _TIF_NEED_RESCHED (1 << TIF_NEED_RESCHED)
#define _TIF_WORK_MASK \
(_TIF_NOTIFY_RESUME | _TIF_SIGPENDING | _TIF_NEED_RESCHED)
#endif /* _ASM_RISCV_THREAD_INFO_H */

322
arch/riscv/kernel/asm-offsets.c Normal file
View File

@ -0,0 +1,322 @@
/*
* Copyright (C) 2012 Regents of the University of California
* Copyright (C) 2017 SiFive
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation, version 2.
*
* This program 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 General Public License for more details.
*/
#define GENERATING_ASM_OFFSETS
#include <linux/kbuild.h>
#include <linux/sched.h>
#include <asm/thread_info.h>
#include <asm/ptrace.h>
void asm_offsets(void)
{
OFFSET(TASK_THREAD_RA, task_struct, thread.ra);
OFFSET(TASK_THREAD_SP, task_struct, thread.sp);
OFFSET(TASK_THREAD_S0, task_struct, thread.s[0]);
OFFSET(TASK_THREAD_S1, task_struct, thread.s[1]);
OFFSET(TASK_THREAD_S2, task_struct, thread.s[2]);
OFFSET(TASK_THREAD_S3, task_struct, thread.s[3]);
OFFSET(TASK_THREAD_S4, task_struct, thread.s[4]);
OFFSET(TASK_THREAD_S5, task_struct, thread.s[5]);
OFFSET(TASK_THREAD_S6, task_struct, thread.s[6]);
OFFSET(TASK_THREAD_S7, task_struct, thread.s[7]);
OFFSET(TASK_THREAD_S8, task_struct, thread.s[8]);
OFFSET(TASK_THREAD_S9, task_struct, thread.s[9]);
OFFSET(TASK_THREAD_S10, task_struct, thread.s[10]);
OFFSET(TASK_THREAD_S11, task_struct, thread.s[11]);
OFFSET(TASK_THREAD_SP, task_struct, thread.sp);
OFFSET(TASK_STACK, task_struct, stack);
OFFSET(TASK_TI, task_struct, thread_info);
OFFSET(TASK_TI_FLAGS, task_struct, thread_info.flags);
OFFSET(TASK_TI_KERNEL_SP, task_struct, thread_info.kernel_sp);
OFFSET(TASK_TI_USER_SP, task_struct, thread_info.user_sp);
OFFSET(TASK_TI_CPU, task_struct, thread_info.cpu);
OFFSET(TASK_THREAD_F0, task_struct, thread.fstate.f[0]);
OFFSET(TASK_THREAD_F1, task_struct, thread.fstate.f[1]);
OFFSET(TASK_THREAD_F2, task_struct, thread.fstate.f[2]);
OFFSET(TASK_THREAD_F3, task_struct, thread.fstate.f[3]);
OFFSET(TASK_THREAD_F4, task_struct, thread.fstate.f[4]);
OFFSET(TASK_THREAD_F5, task_struct, thread.fstate.f[5]);
OFFSET(TASK_THREAD_F6, task_struct, thread.fstate.f[6]);
OFFSET(TASK_THREAD_F7, task_struct, thread.fstate.f[7]);
OFFSET(TASK_THREAD_F8, task_struct, thread.fstate.f[8]);
OFFSET(TASK_THREAD_F9, task_struct, thread.fstate.f[9]);
OFFSET(TASK_THREAD_F10, task_struct, thread.fstate.f[10]);
OFFSET(TASK_THREAD_F11, task_struct, thread.fstate.f[11]);
OFFSET(TASK_THREAD_F12, task_struct, thread.fstate.f[12]);
OFFSET(TASK_THREAD_F13, task_struct, thread.fstate.f[13]);
OFFSET(TASK_THREAD_F14, task_struct, thread.fstate.f[14]);
OFFSET(TASK_THREAD_F15, task_struct, thread.fstate.f[15]);
OFFSET(TASK_THREAD_F16, task_struct, thread.fstate.f[16]);
OFFSET(TASK_THREAD_F17, task_struct, thread.fstate.f[17]);
OFFSET(TASK_THREAD_F18, task_struct, thread.fstate.f[18]);
OFFSET(TASK_THREAD_F19, task_struct, thread.fstate.f[19]);
OFFSET(TASK_THREAD_F20, task_struct, thread.fstate.f[20]);
OFFSET(TASK_THREAD_F21, task_struct, thread.fstate.f[21]);
OFFSET(TASK_THREAD_F22, task_struct, thread.fstate.f[22]);
OFFSET(TASK_THREAD_F23, task_struct, thread.fstate.f[23]);
OFFSET(TASK_THREAD_F24, task_struct, thread.fstate.f[24]);
OFFSET(TASK_THREAD_F25, task_struct, thread.fstate.f[25]);
OFFSET(TASK_THREAD_F26, task_struct, thread.fstate.f[26]);
OFFSET(TASK_THREAD_F27, task_struct, thread.fstate.f[27]);
OFFSET(TASK_THREAD_F28, task_struct, thread.fstate.f[28]);
OFFSET(TASK_THREAD_F29, task_struct, thread.fstate.f[29]);
OFFSET(TASK_THREAD_F30, task_struct, thread.fstate.f[30]);
OFFSET(TASK_THREAD_F31, task_struct, thread.fstate.f[31]);
OFFSET(TASK_THREAD_FCSR, task_struct, thread.fstate.fcsr);
DEFINE(PT_SIZE, sizeof(struct pt_regs));
OFFSET(PT_SEPC, pt_regs, sepc);
OFFSET(PT_RA, pt_regs, ra);
OFFSET(PT_FP, pt_regs, s0);
OFFSET(PT_S0, pt_regs, s0);
OFFSET(PT_S1, pt_regs, s1);
OFFSET(PT_S2, pt_regs, s2);
OFFSET(PT_S3, pt_regs, s3);
OFFSET(PT_S4, pt_regs, s4);
OFFSET(PT_S5, pt_regs, s5);
OFFSET(PT_S6, pt_regs, s6);
OFFSET(PT_S7, pt_regs, s7);
OFFSET(PT_S8, pt_regs, s8);
OFFSET(PT_S9, pt_regs, s9);
OFFSET(PT_S10, pt_regs, s10);
OFFSET(PT_S11, pt_regs, s11);
OFFSET(PT_SP, pt_regs, sp);
OFFSET(PT_TP, pt_regs, tp);
OFFSET(PT_A0, pt_regs, a0);
OFFSET(PT_A1, pt_regs, a1);
OFFSET(PT_A2, pt_regs, a2);
OFFSET(PT_A3, pt_regs, a3);
OFFSET(PT_A4, pt_regs, a4);
OFFSET(PT_A5, pt_regs, a5);
OFFSET(PT_A6, pt_regs, a6);
OFFSET(PT_A7, pt_regs, a7);
OFFSET(PT_T0, pt_regs, t0);
OFFSET(PT_T1, pt_regs, t1);
OFFSET(PT_T2, pt_regs, t2);
OFFSET(PT_T3, pt_regs, t3);
OFFSET(PT_T4, pt_regs, t4);
OFFSET(PT_T5, pt_regs, t5);
OFFSET(PT_T6, pt_regs, t6);
OFFSET(PT_GP, pt_regs, gp);
OFFSET(PT_ORIG_A0, pt_regs, orig_a0);
OFFSET(PT_SSTATUS, pt_regs, sstatus);
OFFSET(PT_SBADADDR, pt_regs, sbadaddr);
OFFSET(PT_SCAUSE, pt_regs, scause);
/*
* THREAD_{F,X}* might be larger than a S-type offset can handle, but
* these are used in performance-sensitive assembly so we can't resort
* to loading the long immediate every time.
*/
DEFINE(TASK_THREAD_RA_RA,
offsetof(struct task_struct, thread.ra)
- offsetof(struct task_struct, thread.ra)
);
DEFINE(TASK_THREAD_SP_RA,
offsetof(struct task_struct, thread.sp)
- offsetof(struct task_struct, thread.ra)
);
DEFINE(TASK_THREAD_S0_RA,
offsetof(struct task_struct, thread.s[0])
- offsetof(struct task_struct, thread.ra)
);
DEFINE(TASK_THREAD_S1_RA,
offsetof(struct task_struct, thread.s[1])
- offsetof(struct task_struct, thread.ra)
);
DEFINE(TASK_THREAD_S2_RA,
offsetof(struct task_struct, thread.s[2])
- offsetof(struct task_struct, thread.ra)
);
DEFINE(TASK_THREAD_S3_RA,
offsetof(struct task_struct, thread.s[3])
- offsetof(struct task_struct, thread.ra)
);
DEFINE(TASK_THREAD_S4_RA,
offsetof(struct task_struct, thread.s[4])
- offsetof(struct task_struct, thread.ra)
);
DEFINE(TASK_THREAD_S5_RA,
offsetof(struct task_struct, thread.s[5])
- offsetof(struct task_struct, thread.ra)
);
DEFINE(TASK_THREAD_S6_RA,
offsetof(struct task_struct, thread.s[6])
- offsetof(struct task_struct, thread.ra)
);
DEFINE(TASK_THREAD_S7_RA,
offsetof(struct task_struct, thread.s[7])
- offsetof(struct task_struct, thread.ra)
);
DEFINE(TASK_THREAD_S8_RA,
offsetof(struct task_struct, thread.s[8])
- offsetof(struct task_struct, thread.ra)
);
DEFINE(TASK_THREAD_S9_RA,
offsetof(struct task_struct, thread.s[9])
- offsetof(struct task_struct, thread.ra)
);
DEFINE(TASK_THREAD_S10_RA,
offsetof(struct task_struct, thread.s[10])
- offsetof(struct task_struct, thread.ra)
);
DEFINE(TASK_THREAD_S11_RA,
offsetof(struct task_struct, thread.s[11])
- offsetof(struct task_struct, thread.ra)
);
DEFINE(TASK_THREAD_F0_F0,
offsetof(struct task_struct, thread.fstate.f[0])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F1_F0,
offsetof(struct task_struct, thread.fstate.f[1])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F2_F0,
offsetof(struct task_struct, thread.fstate.f[2])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F3_F0,
offsetof(struct task_struct, thread.fstate.f[3])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F4_F0,
offsetof(struct task_struct, thread.fstate.f[4])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F5_F0,
offsetof(struct task_struct, thread.fstate.f[5])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F6_F0,
offsetof(struct task_struct, thread.fstate.f[6])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F7_F0,
offsetof(struct task_struct, thread.fstate.f[7])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F8_F0,
offsetof(struct task_struct, thread.fstate.f[8])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F9_F0,
offsetof(struct task_struct, thread.fstate.f[9])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F10_F0,
offsetof(struct task_struct, thread.fstate.f[10])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F11_F0,
offsetof(struct task_struct, thread.fstate.f[11])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F12_F0,
offsetof(struct task_struct, thread.fstate.f[12])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F13_F0,
offsetof(struct task_struct, thread.fstate.f[13])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F14_F0,
offsetof(struct task_struct, thread.fstate.f[14])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F15_F0,
offsetof(struct task_struct, thread.fstate.f[15])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F16_F0,
offsetof(struct task_struct, thread.fstate.f[16])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F17_F0,
offsetof(struct task_struct, thread.fstate.f[17])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F18_F0,
offsetof(struct task_struct, thread.fstate.f[18])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F19_F0,
offsetof(struct task_struct, thread.fstate.f[19])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F20_F0,
offsetof(struct task_struct, thread.fstate.f[20])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F21_F0,
offsetof(struct task_struct, thread.fstate.f[21])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F22_F0,
offsetof(struct task_struct, thread.fstate.f[22])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F23_F0,
offsetof(struct task_struct, thread.fstate.f[23])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F24_F0,
offsetof(struct task_struct, thread.fstate.f[24])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F25_F0,
offsetof(struct task_struct, thread.fstate.f[25])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F26_F0,
offsetof(struct task_struct, thread.fstate.f[26])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F27_F0,
offsetof(struct task_struct, thread.fstate.f[27])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F28_F0,
offsetof(struct task_struct, thread.fstate.f[28])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F29_F0,
offsetof(struct task_struct, thread.fstate.f[29])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F30_F0,
offsetof(struct task_struct, thread.fstate.f[30])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_F31_F0,
offsetof(struct task_struct, thread.fstate.f[31])
- offsetof(struct task_struct, thread.fstate.f[0])
);
DEFINE(TASK_THREAD_FCSR_F0,
offsetof(struct task_struct, thread.fstate.fcsr)
- offsetof(struct task_struct, thread.fstate.f[0])
);
/* The assembler needs access to THREAD_SIZE as well. */
DEFINE(ASM_THREAD_SIZE, THREAD_SIZE);
/*
* We allocate a pt_regs on the stack when entering the kernel. This
* ensures the alignment is sane.
*/
DEFINE(PT_SIZE_ON_STACK, ALIGN(sizeof(struct pt_regs), STACK_ALIGN));
}

464
arch/riscv/kernel/entry.S Normal file
View File

@ -0,0 +1,464 @@
/*
* Copyright (C) 2012 Regents of the University of California
* Copyright (C) 2017 SiFive
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation, version 2.
*
* This program 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 General Public License for more details.
*/
#include <linux/init.h>
#include <linux/linkage.h>
#include <asm/asm.h>
#include <asm/csr.h>
#include <asm/unistd.h>
#include <asm/thread_info.h>
#include <asm/asm-offsets.h>
.text
.altmacro
/*
* Prepares to enter a system call or exception by saving all registers to the
* stack.
*/
.macro SAVE_ALL
LOCAL _restore_kernel_tpsp
LOCAL _save_context
/*
* If coming from userspace, preserve the user thread pointer and load
* the kernel thread pointer. If we came from the kernel, sscratch
* will contain 0, and we should continue on the current TP.
*/
csrrw tp, sscratch, tp
bnez tp, _save_context
_restore_kernel_tpsp:
csrr tp, sscratch
REG_S sp, TASK_TI_KERNEL_SP(tp)
_save_context:
REG_S sp, TASK_TI_USER_SP(tp)
REG_L sp, TASK_TI_KERNEL_SP(tp)
addi sp, sp, -(PT_SIZE_ON_STACK)
REG_S x1, PT_RA(sp)
REG_S x3, PT_GP(sp)
REG_S x5, PT_T0(sp)
REG_S x6, PT_T1(sp)
REG_S x7, PT_T2(sp)
REG_S x8, PT_S0(sp)
REG_S x9, PT_S1(sp)
REG_S x10, PT_A0(sp)
REG_S x11, PT_A1(sp)
REG_S x12, PT_A2(sp)
REG_S x13, PT_A3(sp)
REG_S x14, PT_A4(sp)
REG_S x15, PT_A5(sp)
REG_S x16, PT_A6(sp)
REG_S x17, PT_A7(sp)
REG_S x18, PT_S2(sp)
REG_S x19, PT_S3(sp)
REG_S x20, PT_S4(sp)
REG_S x21, PT_S5(sp)
REG_S x22, PT_S6(sp)
REG_S x23, PT_S7(sp)
REG_S x24, PT_S8(sp)
REG_S x25, PT_S9(sp)
REG_S x26, PT_S10(sp)
REG_S x27, PT_S11(sp)
REG_S x28, PT_T3(sp)
REG_S x29, PT_T4(sp)
REG_S x30, PT_T5(sp)
REG_S x31, PT_T6(sp)
/*
* Disable FPU to detect illegal usage of
* floating point in kernel space
*/
li t0, SR_FS
REG_L s0, TASK_TI_USER_SP(tp)
csrrc s1, sstatus, t0
csrr s2, sepc
csrr s3, sbadaddr
csrr s4, scause
csrr s5, sscratch
REG_S s0, PT_SP(sp)
REG_S s1, PT_SSTATUS(sp)
REG_S s2, PT_SEPC(sp)
REG_S s3, PT_SBADADDR(sp)
REG_S s4, PT_SCAUSE(sp)
REG_S s5, PT_TP(sp)
.endm
/*
* Prepares to return from a system call or exception by restoring all
* registers from the stack.
*/
.macro RESTORE_ALL
REG_L a0, PT_SSTATUS(sp)
REG_L a2, PT_SEPC(sp)
csrw sstatus, a0
csrw sepc, a2
REG_L x1, PT_RA(sp)
REG_L x3, PT_GP(sp)
REG_L x4, PT_TP(sp)
REG_L x5, PT_T0(sp)
REG_L x6, PT_T1(sp)
REG_L x7, PT_T2(sp)
REG_L x8, PT_S0(sp)
REG_L x9, PT_S1(sp)
REG_L x10, PT_A0(sp)
REG_L x11, PT_A1(sp)
REG_L x12, PT_A2(sp)
REG_L x13, PT_A3(sp)
REG_L x14, PT_A4(sp)
REG_L x15, PT_A5(sp)
REG_L x16, PT_A6(sp)
REG_L x17, PT_A7(sp)
REG_L x18, PT_S2(sp)
REG_L x19, PT_S3(sp)
REG_L x20, PT_S4(sp)
REG_L x21, PT_S5(sp)
REG_L x22, PT_S6(sp)
REG_L x23, PT_S7(sp)
REG_L x24, PT_S8(sp)
REG_L x25, PT_S9(sp)
REG_L x26, PT_S10(sp)
REG_L x27, PT_S11(sp)
REG_L x28, PT_T3(sp)
REG_L x29, PT_T4(sp)
REG_L x30, PT_T5(sp)
REG_L x31, PT_T6(sp)
REG_L x2, PT_SP(sp)
.endm
ENTRY(handle_exception)
SAVE_ALL
/*
* Set sscratch register to 0, so that if a recursive exception
* occurs, the exception vector knows it came from the kernel
*/
csrw sscratch, x0
/* Load the global pointer */
.option push
.option norelax
la gp, __global_pointer$
.option pop
la ra, ret_from_exception
/*
* MSB of cause differentiates between
* interrupts and exceptions
*/
bge s4, zero, 1f
/* Handle interrupts */
slli a0, s4, 1
srli a0, a0, 1
move a1, sp /* pt_regs */
tail do_IRQ
1:
/* Handle syscalls */
li t0, EXC_SYSCALL
beq s4, t0, handle_syscall
/* Handle other exceptions */
slli t0, s4, RISCV_LGPTR
la t1, excp_vect_table
la t2, excp_vect_table_end
move a0, sp /* pt_regs */
add t0, t1, t0
/* Check if exception code lies within bounds */
bgeu t0, t2, 1f
REG_L t0, 0(t0)
jr t0
1:
tail do_trap_unknown
handle_syscall:
/* save the initial A0 value (needed in signal handlers) */
REG_S a0, PT_ORIG_A0(sp)
/*
* Advance SEPC to avoid executing the original
* scall instruction on sret
*/
addi s2, s2, 0x4
REG_S s2, PT_SEPC(sp)
/* System calls run with interrupts enabled */
csrs sstatus, SR_IE
/* Trace syscalls, but only if requested by the user. */
REG_L t0, TASK_TI_FLAGS(tp)
andi t0, t0, _TIF_SYSCALL_TRACE
bnez t0, handle_syscall_trace_enter
check_syscall_nr:
/* Check to make sure we don't jump to a bogus syscall number. */
li t0, __NR_syscalls
la s0, sys_ni_syscall
/* Syscall number held in a7 */
bgeu a7, t0, 1f
la s0, sys_call_table
slli t0, a7, RISCV_LGPTR
add s0, s0, t0
REG_L s0, 0(s0)
1:
jalr s0
ret_from_syscall:
/* Set user a0 to kernel a0 */
REG_S a0, PT_A0(sp)
/* Trace syscalls, but only if requested by the user. */
REG_L t0, TASK_TI_FLAGS(tp)
andi t0, t0, _TIF_SYSCALL_TRACE
bnez t0, handle_syscall_trace_exit
ret_from_exception:
REG_L s0, PT_SSTATUS(sp)
csrc sstatus, SR_IE
andi s0, s0, SR_PS
bnez s0, restore_all
resume_userspace:
/* Interrupts must be disabled here so flags are checked atomically */
REG_L s0, TASK_TI_FLAGS(tp) /* current_thread_info->flags */
andi s1, s0, _TIF_WORK_MASK
bnez s1, work_pending
/* Save unwound kernel stack pointer in thread_info */
addi s0, sp, PT_SIZE_ON_STACK
REG_S s0, TASK_TI_KERNEL_SP(tp)
/*
* Save TP into sscratch, so we can find the kernel data structures
* again.
*/
csrw sscratch, tp
restore_all:
RESTORE_ALL
sret
work_pending:
/* Enter slow path for supplementary processing */
la ra, ret_from_exception
andi s1, s0, _TIF_NEED_RESCHED
bnez s1, work_resched
work_notifysig:
/* Handle pending signals and notify-resume requests */
csrs sstatus, SR_IE /* Enable interrupts for do_notify_resume() */
move a0, sp /* pt_regs */
move a1, s0 /* current_thread_info->flags */
tail do_notify_resume
work_resched:
tail schedule
/* Slow paths for ptrace. */
handle_syscall_trace_enter:
move a0, sp
call do_syscall_trace_enter
REG_L a0, PT_A0(sp)
REG_L a1, PT_A1(sp)
REG_L a2, PT_A2(sp)
REG_L a3, PT_A3(sp)
REG_L a4, PT_A4(sp)
REG_L a5, PT_A5(sp)
REG_L a6, PT_A6(sp)
REG_L a7, PT_A7(sp)
j check_syscall_nr
handle_syscall_trace_exit:
move a0, sp
call do_syscall_trace_exit
j ret_from_exception
END(handle_exception)
ENTRY(ret_from_fork)
la ra, ret_from_exception
tail schedule_tail
ENDPROC(ret_from_fork)
ENTRY(ret_from_kernel_thread)
call schedule_tail
/* Call fn(arg) */
la ra, ret_from_exception
move a0, s1
jr s0
ENDPROC(ret_from_kernel_thread)
/*
* Integer register context switch
* The callee-saved registers must be saved and restored.
*
* a0: previous task_struct (must be preserved across the switch)
* a1: next task_struct
*
* The value of a0 and a1 must be preserved by this function, as that's how
* arguments are passed to schedule_tail.
*/
ENTRY(__switch_to)
/* Save context into prev->thread */
li a4, TASK_THREAD_RA
add a3, a0, a4
add a4, a1, a4
REG_S ra, TASK_THREAD_RA_RA(a3)
REG_S sp, TASK_THREAD_SP_RA(a3)
REG_S s0, TASK_THREAD_S0_RA(a3)
REG_S s1, TASK_THREAD_S1_RA(a3)
REG_S s2, TASK_THREAD_S2_RA(a3)
REG_S s3, TASK_THREAD_S3_RA(a3)
REG_S s4, TASK_THREAD_S4_RA(a3)
REG_S s5, TASK_THREAD_S5_RA(a3)
REG_S s6, TASK_THREAD_S6_RA(a3)
REG_S s7, TASK_THREAD_S7_RA(a3)
REG_S s8, TASK_THREAD_S8_RA(a3)
REG_S s9, TASK_THREAD_S9_RA(a3)
REG_S s10, TASK_THREAD_S10_RA(a3)
REG_S s11, TASK_THREAD_S11_RA(a3)
/* Restore context from next->thread */
REG_L ra, TASK_THREAD_RA_RA(a4)
REG_L sp, TASK_THREAD_SP_RA(a4)
REG_L s0, TASK_THREAD_S0_RA(a4)
REG_L s1, TASK_THREAD_S1_RA(a4)
REG_L s2, TASK_THREAD_S2_RA(a4)
REG_L s3, TASK_THREAD_S3_RA(a4)
REG_L s4, TASK_THREAD_S4_RA(a4)
REG_L s5, TASK_THREAD_S5_RA(a4)
REG_L s6, TASK_THREAD_S6_RA(a4)
REG_L s7, TASK_THREAD_S7_RA(a4)
REG_L s8, TASK_THREAD_S8_RA(a4)
REG_L s9, TASK_THREAD_S9_RA(a4)
REG_L s10, TASK_THREAD_S10_RA(a4)
REG_L s11, TASK_THREAD_S11_RA(a4)
/* Swap the CPU entry around. */
lw a3, TASK_TI_CPU(a0)
lw a4, TASK_TI_CPU(a1)
sw a3, TASK_TI_CPU(a1)
sw a4, TASK_TI_CPU(a0)
#if TASK_TI != 0
#error "TASK_TI != 0: tp will contain a 'struct thread_info', not a 'struct task_struct' so get_current() won't work."
addi tp, a1, TASK_TI
#else
move tp, a1
#endif
ret
ENDPROC(__switch_to)
ENTRY(__fstate_save)
li a2, TASK_THREAD_F0
add a0, a0, a2
li t1, SR_FS
csrs sstatus, t1
frcsr t0
fsd f0, TASK_THREAD_F0_F0(a0)
fsd f1, TASK_THREAD_F1_F0(a0)
fsd f2, TASK_THREAD_F2_F0(a0)
fsd f3, TASK_THREAD_F3_F0(a0)
fsd f4, TASK_THREAD_F4_F0(a0)
fsd f5, TASK_THREAD_F5_F0(a0)
fsd f6, TASK_THREAD_F6_F0(a0)
fsd f7, TASK_THREAD_F7_F0(a0)
fsd f8, TASK_THREAD_F8_F0(a0)
fsd f9, TASK_THREAD_F9_F0(a0)
fsd f10, TASK_THREAD_F10_F0(a0)
fsd f11, TASK_THREAD_F11_F0(a0)
fsd f12, TASK_THREAD_F12_F0(a0)
fsd f13, TASK_THREAD_F13_F0(a0)
fsd f14, TASK_THREAD_F14_F0(a0)
fsd f15, TASK_THREAD_F15_F0(a0)
fsd f16, TASK_THREAD_F16_F0(a0)
fsd f17, TASK_THREAD_F17_F0(a0)
fsd f18, TASK_THREAD_F18_F0(a0)
fsd f19, TASK_THREAD_F19_F0(a0)
fsd f20, TASK_THREAD_F20_F0(a0)
fsd f21, TASK_THREAD_F21_F0(a0)
fsd f22, TASK_THREAD_F22_F0(a0)
fsd f23, TASK_THREAD_F23_F0(a0)
fsd f24, TASK_THREAD_F24_F0(a0)
fsd f25, TASK_THREAD_F25_F0(a0)
fsd f26, TASK_THREAD_F26_F0(a0)
fsd f27, TASK_THREAD_F27_F0(a0)
fsd f28, TASK_THREAD_F28_F0(a0)
fsd f29, TASK_THREAD_F29_F0(a0)
fsd f30, TASK_THREAD_F30_F0(a0)
fsd f31, TASK_THREAD_F31_F0(a0)
sw t0, TASK_THREAD_FCSR_F0(a0)
csrc sstatus, t1
ret
ENDPROC(__fstate_save)
ENTRY(__fstate_restore)
li a2, TASK_THREAD_F0
add a0, a0, a2
li t1, SR_FS
lw t0, TASK_THREAD_FCSR_F0(a0)
csrs sstatus, t1
fld f0, TASK_THREAD_F0_F0(a0)
fld f1, TASK_THREAD_F1_F0(a0)
fld f2, TASK_THREAD_F2_F0(a0)
fld f3, TASK_THREAD_F3_F0(a0)
fld f4, TASK_THREAD_F4_F0(a0)
fld f5, TASK_THREAD_F5_F0(a0)
fld f6, TASK_THREAD_F6_F0(a0)
fld f7, TASK_THREAD_F7_F0(a0)
fld f8, TASK_THREAD_F8_F0(a0)
fld f9, TASK_THREAD_F9_F0(a0)
fld f10, TASK_THREAD_F10_F0(a0)
fld f11, TASK_THREAD_F11_F0(a0)
fld f12, TASK_THREAD_F12_F0(a0)
fld f13, TASK_THREAD_F13_F0(a0)
fld f14, TASK_THREAD_F14_F0(a0)
fld f15, TASK_THREAD_F15_F0(a0)
fld f16, TASK_THREAD_F16_F0(a0)
fld f17, TASK_THREAD_F17_F0(a0)
fld f18, TASK_THREAD_F18_F0(a0)
fld f19, TASK_THREAD_F19_F0(a0)
fld f20, TASK_THREAD_F20_F0(a0)
fld f21, TASK_THREAD_F21_F0(a0)
fld f22, TASK_THREAD_F22_F0(a0)
fld f23, TASK_THREAD_F23_F0(a0)
fld f24, TASK_THREAD_F24_F0(a0)
fld f25, TASK_THREAD_F25_F0(a0)
fld f26, TASK_THREAD_F26_F0(a0)
fld f27, TASK_THREAD_F27_F0(a0)
fld f28, TASK_THREAD_F28_F0(a0)
fld f29, TASK_THREAD_F29_F0(a0)
fld f30, TASK_THREAD_F30_F0(a0)
fld f31, TASK_THREAD_F31_F0(a0)
fscsr t0
csrc sstatus, t1
ret
ENDPROC(__fstate_restore)
.section ".rodata"
/* Exception vector table */
ENTRY(excp_vect_table)
RISCV_PTR do_trap_insn_misaligned
RISCV_PTR do_trap_insn_fault
RISCV_PTR do_trap_insn_illegal
RISCV_PTR do_trap_break
RISCV_PTR do_trap_load_misaligned
RISCV_PTR do_trap_load_fault
RISCV_PTR do_trap_store_misaligned
RISCV_PTR do_trap_store_fault
RISCV_PTR do_trap_ecall_u /* system call, gets intercepted */
RISCV_PTR do_trap_ecall_s
RISCV_PTR do_trap_unknown
RISCV_PTR do_trap_ecall_m
RISCV_PTR do_page_fault /* instruction page fault */
RISCV_PTR do_page_fault /* load page fault */
RISCV_PTR do_trap_unknown
RISCV_PTR do_page_fault /* store page fault */
excp_vect_table_end:
END(excp_vect_table)

129
arch/riscv/kernel/process.c Normal file
View File

@ -0,0 +1,129 @@
/*
* Copyright (C) 2009 Sunplus Core Technology Co., Ltd.
* Chen Liqin <liqin.chen@sunplusct.com>
* Lennox Wu <lennox.wu@sunplusct.com>
* Copyright (C) 2012 Regents of the University of California
* Copyright (C) 2017 SiFive
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see the file COPYING, or write
* to the Free Software Foundation, Inc.,
*/
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/sched/task_stack.h>
#include <linux/tick.h>
#include <linux/ptrace.h>
#include <asm/unistd.h>
#include <asm/uaccess.h>
#include <asm/processor.h>
#include <asm/csr.h>
#include <asm/string.h>
#include <asm/switch_to.h>
extern asmlinkage void ret_from_fork(void);
extern asmlinkage void ret_from_kernel_thread(void);
void arch_cpu_idle(void)
{
wait_for_interrupt();
local_irq_enable();
}
void show_regs(struct pt_regs *regs)
{
show_regs_print_info(KERN_DEFAULT);
pr_cont("sepc: " REG_FMT " ra : " REG_FMT " sp : " REG_FMT "\n",
regs->sepc, regs->ra, regs->sp);
pr_cont(" gp : " REG_FMT " tp : " REG_FMT " t0 : " REG_FMT "\n",
regs->gp, regs->tp, regs->t0);
pr_cont(" t1 : " REG_FMT " t2 : " REG_FMT " s0 : " REG_FMT "\n",
regs->t1, regs->t2, regs->s0);
pr_cont(" s1 : " REG_FMT " a0 : " REG_FMT " a1 : " REG_FMT "\n",
regs->s1, regs->a0, regs->a1);
pr_cont(" a2 : " REG_FMT " a3 : " REG_FMT " a4 : " REG_FMT "\n",
regs->a2, regs->a3, regs->a4);
pr_cont(" a5 : " REG_FMT " a6 : " REG_FMT " a7 : " REG_FMT "\n",
regs->a5, regs->a6, regs->a7);
pr_cont(" s2 : " REG_FMT " s3 : " REG_FMT " s4 : " REG_FMT "\n",
regs->s2, regs->s3, regs->s4);
pr_cont(" s5 : " REG_FMT " s6 : " REG_FMT " s7 : " REG_FMT "\n",
regs->s5, regs->s6, regs->s7);
pr_cont(" s8 : " REG_FMT " s9 : " REG_FMT " s10: " REG_FMT "\n",
regs->s8, regs->s9, regs->s10);
pr_cont(" s11: " REG_FMT " t3 : " REG_FMT " t4 : " REG_FMT "\n",
regs->s11, regs->t3, regs->t4);
pr_cont(" t5 : " REG_FMT " t6 : " REG_FMT "\n",
regs->t5, regs->t6);
pr_cont("sstatus: " REG_FMT " sbadaddr: " REG_FMT " scause: " REG_FMT "\n",
regs->sstatus, regs->sbadaddr, regs->scause);
}
void start_thread(struct pt_regs *regs, unsigned long pc,
unsigned long sp)
{
regs->sstatus = SR_PIE /* User mode, irqs on */ | SR_FS_INITIAL;
regs->sepc = pc;
regs->sp = sp;
set_fs(USER_DS);
}
void flush_thread(void)
{
/*
* Reset FPU context
* frm: round to nearest, ties to even (IEEE default)
* fflags: accrued exceptions cleared
*/
memset(&current->thread.fstate, 0, sizeof(current->thread.fstate));
}
int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
{
fstate_save(src, task_pt_regs(src));
*dst = *src;
return 0;
}
int copy_thread(unsigned long clone_flags, unsigned long usp,
unsigned long arg, struct task_struct *p)
{
struct pt_regs *childregs = task_pt_regs(p);
/* p->thread holds context to be restored by __switch_to() */
if (unlikely(p->flags & PF_KTHREAD)) {
/* Kernel thread */
const register unsigned long gp __asm__ ("gp");
memset(childregs, 0, sizeof(struct pt_regs));
childregs->gp = gp;
childregs->sstatus = SR_PS | SR_PIE; /* Supervisor, irqs on */
p->thread.ra = (unsigned long)ret_from_kernel_thread;
p->thread.s[0] = usp; /* fn */
p->thread.s[1] = arg;
} else {
*childregs = *(current_pt_regs());
if (usp) /* User fork */
childregs->sp = usp;
if (clone_flags & CLONE_SETTLS)
childregs->tp = childregs->a5;
childregs->a0 = 0; /* Return value of fork() */
p->thread.ra = (unsigned long)ret_from_fork;
}
p->thread.sp = (unsigned long)childregs; /* kernel sp */
return 0;
}