process.c

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/*
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Copyright (C) 1994 - 1999, 2000 by Ralf Baechle and others.
 * Copyright (C) 2005, 2006 by Ralf Baechle ([email protected])
 * Copyright (C) 1999, 2000 Silicon Graphics, Inc.
 * Copyright (C) 2004 Thiemo Seufer
 */
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/tick.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/stddef.h>
#include <linux/unistd.h>
#include <linux/export.h>
#include <linux/ptrace.h>
#include <linux/mman.h>
#include <linux/personality.h>
#include <linux/sys.h>
#include <linux/user.h>
#include <linux/init.h>
#include <linux/completion.h>
#include <linux/kallsyms.h>
#include <linux/random.h>

#include <asm/asm.h>
#include <asm/bootinfo.h>
#include <asm/cpu.h>
#include <asm/dsp.h>
#include <asm/fpu.h>
#include <asm/pgtable.h>
#include <asm/mipsregs.h>
#include <asm/processor.h>
#include <asm/uaccess.h>
#include <asm/io.h>
#include <asm/elf.h>
#include <asm/isadep.h>
#include <asm/inst.h>
#include <asm/stacktrace.h>

/*
 * The idle thread. There's no useful work to be done, so just try to conserve
 * power and have a low exit latency (ie sit in a loop waiting for somebody to
 * say that they'd like to reschedule)
 */
void __noreturn cpu_idle(void)
{
    int cpu;

    /* CPU is going idle. */
    cpu = smp_processor_id();

    /* endless idle loop with no priority at all */
    while (1) {
        tick_nohz_idle_enter();
        rcu_idle_enter();
        while (!need_resched() && cpu_online(cpu)) {
#ifdef CONFIG_MIPS_MT_SMTC
            extern void smtc_idle_loop_hook(void);

            smtc_idle_loop_hook();
#endif

            if (cpu_wait) {
                /* Don't trace irqs off for idle */
                stop_critical_timings();
                (*cpu_wait)();
                start_critical_timings();
            }
        }
#ifdef CONFIG_HOTPLUG_CPU
        if (!cpu_online(cpu) && !cpu_isset(cpu, cpu_callin_map) &&
            (system_state == SYSTEM_RUNNING ||
             system_state == SYSTEM_BOOTING))
            play_dead();
#endif
        rcu_idle_exit();
        tick_nohz_idle_exit();
        schedule_preempt_disabled();
    }
}

asmlinkage void ret_from_fork(void);

void start_thread(struct pt_regs * regs, unsigned long pc, unsigned long sp)
{
    unsigned long status;

    /* New thread loses kernel privileges. */
    status = regs->cp0_status & ~(ST0_CU0|ST0_CU1|ST0_FR|KU_MASK);
#ifdef CONFIG_64BIT
    status |= test_thread_flag(TIF_32BIT_REGS) ? 0 : ST0_FR;
#endif
    status |= KU_USER;
    regs->cp0_status = status;
    clear_used_math();
    clear_fpu_owner();
    if (cpu_has_dsp)
        __init_dsp();
    regs->cp0_epc = pc;
    regs->regs[29] = sp;
}

void exit_thread(void)
{
}

void flush_thread(void)
{
}

int copy_thread(unsigned long clone_flags, unsigned long usp,
    unsigned long unused, struct task_struct *p, struct pt_regs *regs)
{
    struct thread_info *ti = task_thread_info(p);
    struct pt_regs *childregs;
    unsigned long childksp;
    p->set_child_tid = p->clear_child_tid = NULL;

    childksp = (unsigned long)task_stack_page(p) + THREAD_SIZE - 32;

    preempt_disable();

    if (is_fpu_owner())
        save_fp(p);

    if (cpu_has_dsp)
        save_dsp(p);

    preempt_enable();

    /* set up new TSS. */
    childregs = (struct pt_regs *) childksp - 1;
    /*  Put the stack after the struct pt_regs.  */
    childksp = (unsigned long) childregs;
    *childregs = *regs;
    childregs->regs[7] = 0; /* Clear error flag */

    childregs->regs[2] = 0; /* Child gets zero as return value */

    if (childregs->cp0_status & ST0_CU0) {
        childregs->regs[28] = (unsigned long) ti;
        childregs->regs[29] = childksp;
        ti->addr_limit = KERNEL_DS;
    } else {
        childregs->regs[29] = usp;
        ti->addr_limit = USER_DS;
    }
    p->thread.reg29 = (unsigned long) childregs;
    p->thread.reg31 = (unsigned long) ret_from_fork;

    /*
     * New tasks lose permission to use the fpu. This accelerates context
     * switching for most programs since they don't use the fpu.
     */
    p->thread.cp0_status = read_c0_status() & ~(ST0_CU2|ST0_CU1);
    childregs->cp0_status &= ~(ST0_CU2|ST0_CU1);

#ifdef CONFIG_MIPS_MT_SMTC
    /*
     * SMTC restores TCStatus after Status, and the CU bits
     * are aliased there.
     */
    childregs->cp0_tcstatus &= ~(ST0_CU2|ST0_CU1);
#endif
    clear_tsk_thread_flag(p, TIF_USEDFPU);

#ifdef CONFIG_MIPS_MT_FPAFF
    clear_tsk_thread_flag(p, TIF_FPUBOUND);
#endif /* CONFIG_MIPS_MT_FPAFF */

    if (clone_flags & CLONE_SETTLS)
        ti->tp_value = regs->regs[7];

    return 0;
}

/* Fill in the fpu structure for a core dump.. */
int dump_fpu(struct pt_regs *regs, elf_fpregset_t *r)
{
    memcpy(r, &current->thread.fpu, sizeof(current->thread.fpu));

    return 1;
}

void elf_dump_regs(elf_greg_t *gp, struct pt_regs *regs)
{
    int i;

    for (i = 0; i < EF_R0; i++)
        gp[i] = 0;
    gp[EF_R0] = 0;
    for (i = 1; i <= 31; i++)
        gp[EF_R0 + i] = regs->regs[i];
    gp[EF_R26] = 0;
    gp[EF_R27] = 0;
    gp[EF_LO] = regs->lo;
    gp[EF_HI] = regs->hi;
    gp[EF_CP0_EPC] = regs->cp0_epc;
    gp[EF_CP0_BADVADDR] = regs->cp0_badvaddr;
    gp[EF_CP0_STATUS] = regs->cp0_status;
    gp[EF_CP0_CAUSE] = regs->cp0_cause;
#ifdef EF_UNUSED0
    gp[EF_UNUSED0] = 0;
#endif
}

int dump_task_regs(struct task_struct *tsk, elf_gregset_t *regs)
{
    elf_dump_regs(*regs, task_pt_regs(tsk));
    return 1;
}

int dump_task_fpu(struct task_struct *t, elf_fpregset_t *fpr)
{
    memcpy(fpr, &t->thread.fpu, sizeof(current->thread.fpu));

    return 1;
}

/*
 * Create a kernel thread
 */
static void __noreturn kernel_thread_helper(void *arg, int (*fn)(void *))
{
    do_exit(fn(arg));
}

long kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
{
    struct pt_regs regs;

    memset(&regs, 0, sizeof(regs));

    regs.regs[4] = (unsigned long) arg;
    regs.regs[5] = (unsigned long) fn;
    regs.cp0_epc = (unsigned long) kernel_thread_helper;
    regs.cp0_status = read_c0_status();
#if defined(CONFIG_CPU_R3000) || defined(CONFIG_CPU_TX39XX)
    regs.cp0_status = (regs.cp0_status & ~(ST0_KUP | ST0_IEP | ST0_IEC)) |
              ((regs.cp0_status & (ST0_KUC | ST0_IEC)) << 2);
#else
    regs.cp0_status |= ST0_EXL;
#endif

    /* Ok, create the new process.. */
    return do_fork(flags | CLONE_VM | CLONE_UNTRACED, 0, &regs, 0, NULL, NULL);
}

/*
 *
 */
struct mips_frame_info {
    void        *func;
    unsigned long   func_size;
    int     frame_size;
    int     pc_offset;
};

static inline int is_ra_save_ins(union mips_instruction *ip)
{
    /* sw / sd $ra, offset($sp) */
    return (ip->i_format.opcode == sw_op || ip->i_format.opcode == sd_op) &&
        ip->i_format.rs == 29 &&
        ip->i_format.rt == 31;
}

static inline int is_jal_jalr_jr_ins(union mips_instruction *ip)
{
    if (ip->j_format.opcode == jal_op)
        return 1;
    if (ip->r_format.opcode != spec_op)
        return 0;
    return ip->r_format.func == jalr_op || ip->r_format.func == jr_op;
}

static inline int is_sp_move_ins(union mips_instruction *ip)
{
    /* addiu/daddiu sp,sp,-imm */
    if (ip->i_format.rs != 29 || ip->i_format.rt != 29)
        return 0;
    if (ip->i_format.opcode == addiu_op || ip->i_format.opcode == daddiu_op)
        return 1;
    return 0;
}

static int get_frame_info(struct mips_frame_info *info)
{
    union mips_instruction *ip = info->func;
    unsigned max_insns = info->func_size / sizeof(union mips_instruction);
    unsigned i;

    info->pc_offset = -1;
    info->frame_size = 0;

    if (!ip)
        goto err;

    if (max_insns == 0)
        max_insns = 128U;   /* unknown function size */
    max_insns = min(128U, max_insns);

    for (i = 0; i < max_insns; i++, ip++) {

        if (is_jal_jalr_jr_ins(ip))
            break;
        if (!info->frame_size) {
            if (is_sp_move_ins(ip))
                info->frame_size = - ip->i_format.simmediate;
            continue;
        }
        if (info->pc_offset == -1 && is_ra_save_ins(ip)) {
            info->pc_offset =
                ip->i_format.simmediate / sizeof(long);
            break;
        }
    }
    if (info->frame_size && info->pc_offset >= 0) /* nested */
        return 0;
    if (info->pc_offset < 0) /* leaf */
        return 1;
    /* prologue seems boggus... */
err:
    return -1;
}

static struct mips_frame_info schedule_mfi __read_mostly;

static int __init frame_info_init(void)
{
    unsigned long size = 0;
#ifdef CONFIG_KALLSYMS
    unsigned long ofs;

    kallsyms_lookup_size_offset((unsigned long)schedule, &size, &ofs);
#endif
    schedule_mfi.func = schedule;
    schedule_mfi.func_size = size;

    get_frame_info(&schedule_mfi);

    /*
     * Without schedule() frame info, result given by
     * thread_saved_pc() and get_wchan() are not reliable.
     */
    if (schedule_mfi.pc_offset < 0)
        printk("Can't analyze schedule() prologue at %p\n", schedule);

    return 0;
}

arch_initcall(frame_info_init);

/*
 * Return saved PC of a blocked thread.
 */
unsigned long thread_saved_pc(struct task_struct *tsk)
{
    struct thread_struct *t = &tsk->thread;

    /* New born processes are a special case */
    if (t->reg31 == (unsigned long) ret_from_fork)
        return t->reg31;
    if (schedule_mfi.pc_offset < 0)
        return 0;
    return ((unsigned long *)t->reg29)[schedule_mfi.pc_offset];
}


#ifdef CONFIG_KALLSYMS
/* generic stack unwinding function */
unsigned long notrace unwind_stack_by_address(unsigned long stack_page,
                          unsigned long *sp,
                          unsigned long pc,
                          unsigned long *ra)
{
    struct mips_frame_info info;
    unsigned long size, ofs;
    int leaf;
    extern void ret_from_irq(void);
    extern void ret_from_exception(void);

    if (!stack_page)
        return 0;

    /*
     * If we reached the bottom of interrupt context,
     * return saved pc in pt_regs.
     */
    if (pc == (unsigned long)ret_from_irq ||
        pc == (unsigned long)ret_from_exception) {
        struct pt_regs *regs;
        if (*sp >= stack_page &&
            *sp + sizeof(*regs) <= stack_page + THREAD_SIZE - 32) {
            regs = (struct pt_regs *)*sp;
            pc = regs->cp0_epc;
            if (__kernel_text_address(pc)) {
                *sp = regs->regs[29];
                *ra = regs->regs[31];
                return pc;
            }
        }
        return 0;
    }
    if (!kallsyms_lookup_size_offset(pc, &size, &ofs))
        return 0;
    /*
     * Return ra if an exception occurred at the first instruction
     */
    if (unlikely(ofs == 0)) {
        pc = *ra;
        *ra = 0;
        return pc;
    }

    info.func = (void *)(pc - ofs);
    info.func_size = ofs;   /* analyze from start to ofs */
    leaf = get_frame_info(&info);
    if (leaf < 0)
        return 0;

    if (*sp < stack_page ||
        *sp + info.frame_size > stack_page + THREAD_SIZE - 32)
        return 0;

    if (leaf)
        /*
         * For some extreme cases, get_frame_info() can
         * consider wrongly a nested function as a leaf
         * one. In that cases avoid to return always the
         * same value.
         */
        pc = pc != *ra ? *ra : 0;
    else
        pc = ((unsigned long *)(*sp))[info.pc_offset];

    *sp += info.frame_size;
    *ra = 0;
    return __kernel_text_address(pc) ? pc : 0;
}
EXPORT_SYMBOL(unwind_stack_by_address);

/* used by show_backtrace() */
unsigned long unwind_stack(struct task_struct *task, unsigned long *sp,
               unsigned long pc, unsigned long *ra)
{
    unsigned long stack_page = (unsigned long)task_stack_page(task);
    return unwind_stack_by_address(stack_page, sp, pc, ra);
}
#endif

/*
 * get_wchan - a maintenance nightmare^W^Wpain in the ass ...
 */
unsigned long get_wchan(struct task_struct *task)
{
    unsigned long pc = 0;
#ifdef CONFIG_KALLSYMS
    unsigned long sp;
    unsigned long ra = 0;
#endif

    if (!task || task == current || task->state == TASK_RUNNING)
        goto out;
    if (!task_stack_page(task))
        goto out;

    pc = thread_saved_pc(task);

#ifdef CONFIG_KALLSYMS
    sp = task->thread.reg29 + schedule_mfi.frame_size;

    while (in_sched_functions(pc))
        pc = unwind_stack(task, &sp, pc, &ra);
#endif

out:
    return pc;
}

/*
 * Don't forget that the stack pointer must be aligned on a 8 bytes
 * boundary for 32-bits ABI and 16 bytes for 64-bits ABI.
 */
unsigned long arch_align_stack(unsigned long sp)
{
    if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
        sp -= get_random_int() & ~PAGE_MASK;

    return sp & ALMASK;
}