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process.c

/*
 * 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 (ralf@linux-mips.org)
 * Copyright (C) 1999, 2000 Silicon Graphics, Inc.
 * Copyright (C) 2004 Thiemo Seufer
 */
#include <linux/errno.h>
#include <linux/module.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/ptrace.h>
#include <linux/slab.h>
#include <linux/mman.h>
#include <linux/personality.h>
#include <linux/sys.h>
#include <linux/user.h>
#include <linux/a.out.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/system.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)
{
      /* endless idle loop with no priority at all */
      while (1) {
            tick_nohz_stop_sched_tick(1);
            while (!need_resched()) {
#ifdef CONFIG_SMTC_IDLE_HOOK_DEBUG
                  extern void smtc_idle_loop_hook(void);

                  smtc_idle_loop_hook();
#endif
                  if (cpu_wait)
                        (*cpu_wait)();
            }
            tick_nohz_restart_sched_tick();
            preempt_enable_no_resched();
            schedule();
            preempt_disable();
      }
}

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;
      current_thread_info()->addr_limit = USER_DS;
}

void exit_thread(void)
{
}

void flush_thread(void)
{
}

int copy_thread(int nr, 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;
      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;
      *childregs = *regs;
      childregs->regs[7] = 0; /* Clear error flag */

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

      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);
      clear_tsk_thread_flag(p, TIF_USEDFPU);

#ifdef CONFIG_MIPS_MT_FPAFF
      clear_tsk_thread_flag(p, TIF_FPUBOUND);

      /*
       * FPU affinity support is cleaner if we track the
       * user-visible CPU affinity from the very beginning.
       * The generic cpus_allowed mask will already have
       * been copied from the parent before copy_thread
       * is invoked.
       */
      p->thread.user_cpus_allowed = p->cpus_allowed;
#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
/* 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;
      struct mips_frame_info info;
      unsigned long size, ofs;
      int leaf;
      extern void ret_from_irq(void);
      extern void ret_from_exception(void);

      stack_page = (unsigned long)task_stack_page(task);
      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 occured 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;
}
#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;
}

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