unwind.c

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/*
 * Backtrace support for Microblaze
 *
 * Copyright (C) 2010  Digital Design Corporation
 *
 * Based on arch/sh/kernel/cpu/sh5/unwind.c code which is:
 * Copyright (C) 2004  Paul Mundt
 * Copyright (C) 2004  Richard Curnow
 *
 * 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.
 */

/* #define DEBUG 1 */
#include <linux/kallsyms.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/stacktrace.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/module.h>
#include <linux/io.h>
#include <asm/sections.h>
#include <asm/exceptions.h>
#include <asm/unwind.h>
#include <asm/switch_to.h>

struct stack_trace;

/*
 * On Microblaze, finding the previous stack frame is a little tricky.
 * At this writing (3/2010), Microblaze does not support CONFIG_FRAME_POINTERS,
 * and even if it did, gcc (4.1.2) does not store the frame pointer at
 * a consistent offset within each frame. To determine frame size, it is
 * necessary to search for the assembly instruction that creates or reclaims
 * the frame and extract the size from it.
 *
 * Microblaze stores the stack pointer in r1, and creates a frame via
 *
 *     addik r1, r1, -FRAME_SIZE
 *
 * The frame is reclaimed via
 *
 *     addik r1, r1, FRAME_SIZE
 *
 * Frame creation occurs at or near the top of a function.
 * Depending on the compiler, reclaim may occur at the end, or before
 * a mid-function return.
 *
 * A stack frame is usually not created in a leaf function.
 *
 */

inline long get_frame_size(unsigned long instr)
{
    return abs((s16)(instr & 0xFFFF));
}

static unsigned long *find_frame_creation(unsigned long *pc)
{
    int i;

    /* NOTE: Distance to search is arbitrary
     *   250 works well for most things,
     *   750 picks up things like tcp_recvmsg(),
     *  1000 needed for fat_fill_super()
     */
    for (i = 0; i < 1000; i++, pc--) {
        unsigned long instr;
        s16 frame_size;

        if (!kernel_text_address((unsigned long) pc))
            return NULL;

        instr = *pc;

        /* addik r1, r1, foo ? */
        if ((instr & 0xFFFF0000) != 0x30210000)
            continue;   /* No */

        frame_size = get_frame_size(instr);
        if ((frame_size < 8) || (frame_size & 3)) {
            pr_debug("    Invalid frame size %d at 0x%p\n",
                 frame_size, pc);
            return NULL;
        }

        pr_debug("    Found frame creation at 0x%p, size %d\n", pc,
             frame_size);
        return pc;
    }

    return NULL;
}

static int lookup_prev_stack_frame(unsigned long fp, unsigned long pc,
                   unsigned long leaf_return,
                   unsigned long *pprev_fp,
                   unsigned long *pprev_pc)
{
    unsigned long *prologue = NULL;

    /* _switch_to is a special leaf function */
    if (pc != (unsigned long) &_switch_to)
        prologue = find_frame_creation((unsigned long *)pc);

    if (prologue) {
        long frame_size = get_frame_size(*prologue);

        *pprev_fp = fp + frame_size;
        *pprev_pc = *(unsigned long *)fp;
    } else {
        if (!leaf_return)
            return -EINVAL;
        *pprev_pc = leaf_return;
        *pprev_fp = fp;
    }

    /* NOTE: don't check kernel_text_address here, to allow display
     *   of userland return address
     */
    return (!*pprev_pc || (*pprev_pc & 3)) ? -EINVAL : 0;
}

static void microblaze_unwind_inner(struct task_struct *task,
                    unsigned long pc, unsigned long fp,
                    unsigned long leaf_return,
                    struct stack_trace *trace);

#ifdef CONFIG_MMU
static inline void unwind_trap(struct task_struct *task, unsigned long pc,
                unsigned long fp, struct stack_trace *trace)
{
    /* To be implemented */
}
#else
static inline void unwind_trap(struct task_struct *task, unsigned long pc,
                unsigned long fp, struct stack_trace *trace)
{
    const struct pt_regs *regs = (const struct pt_regs *) fp;
    microblaze_unwind_inner(task, regs->pc, regs->r1, regs->r15, trace);
}
#endif

static void microblaze_unwind_inner(struct task_struct *task,
                 unsigned long pc, unsigned long fp,
                 unsigned long leaf_return,
                 struct stack_trace *trace)
{
    int ofs = 0;

    pr_debug("    Unwinding with PC=%p, FP=%p\n", (void *)pc, (void *)fp);
    if (!pc || !fp || (pc & 3) || (fp & 3)) {
        pr_debug("    Invalid state for unwind, aborting\n");
        return;
    }
    for (; pc != 0;) {
        unsigned long next_fp, next_pc = 0;
        unsigned long return_to = pc +  2 * sizeof(unsigned long);
        const struct trap_handler_info *handler =
            &microblaze_trap_handlers;

        /* Is previous function the HW exception handler? */
        if ((return_to >= (unsigned long)&_hw_exception_handler)
            &&(return_to < (unsigned long)&ex_handler_unhandled)) {
            /*
             * HW exception handler doesn't save all registers,
             * so we open-code a special case of unwind_trap()
             */
#ifndef CONFIG_MMU
            const struct pt_regs *regs =
                (const struct pt_regs *) fp;
#endif
            pr_info("HW EXCEPTION\n");
#ifndef CONFIG_MMU
            microblaze_unwind_inner(task, regs->r17 - 4,
                        fp + EX_HANDLER_STACK_SIZ,
                        regs->r15, trace);
#endif
            return;
        }

        /* Is previous function a trap handler? */
        for (; handler->start_addr; ++handler) {
            if ((return_to >= handler->start_addr)
                && (return_to <= handler->end_addr)) {
                if (!trace)
                    pr_info("%s\n", handler->trap_name);
                unwind_trap(task, pc, fp, trace);
                return;
            }
        }
        pc -= ofs;

        if (trace) {
#ifdef CONFIG_STACKTRACE
            if (trace->skip > 0)
                trace->skip--;
            else
                trace->entries[trace->nr_entries++] = pc;

            if (trace->nr_entries >= trace->max_entries)
                break;
#endif
        } else {
            /* Have we reached userland? */
            if (unlikely(pc == task_pt_regs(task)->pc)) {
                pr_info("[<%p>] PID %lu [%s]\n",
                    (void *) pc,
                    (unsigned long) task->pid,
                    task->comm);
                break;
            } else
                print_ip_sym(pc);
        }

        /* Stop when we reach anything not part of the kernel */
        if (!kernel_text_address(pc))
            break;

        if (lookup_prev_stack_frame(fp, pc, leaf_return, &next_fp,
                        &next_pc) == 0) {
            ofs = sizeof(unsigned long);
            pc = next_pc & ~3;
            fp = next_fp;
            leaf_return = 0;
        } else {
            pr_debug("    Failed to find previous stack frame\n");
            break;
        }

        pr_debug("    Next PC=%p, next FP=%p\n",
             (void *)next_pc, (void *)next_fp);
    }
}

void microblaze_unwind(struct task_struct *task, struct stack_trace *trace)
{
    if (task) {
        if (task == current) {
            const struct pt_regs *regs = task_pt_regs(task);
            microblaze_unwind_inner(task, regs->pc, regs->r1,
                        regs->r15, trace);
        } else {
            struct thread_info *thread_info =
                (struct thread_info *)(task->stack);
            const struct cpu_context *cpu_context =
                &thread_info->cpu_context;

            microblaze_unwind_inner(task,
                        (unsigned long) &_switch_to,
                        cpu_context->r1,
                        cpu_context->r15, trace);
        }
    } else {
        unsigned long pc, fp;

        __asm__ __volatile__ ("or %0, r1, r0" : "=r" (fp));

        __asm__ __volatile__ (
            "brlid %0, 0f;"
            "nop;"
            "0:"
            : "=r" (pc)
        );

        /* Since we are not a leaf function, use leaf_return = 0 */
        microblaze_unwind_inner(current, pc, fp, 0, trace);
    }
}