unwind.c

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/*
 * arch/arm/kernel/unwind.c
 *
 * Copyright (C) 2008 ARM Limited
 *
 * 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.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 *
 *
 * Stack unwinding support for ARM
 *
 * An ARM EABI version of gcc is required to generate the unwind
 * tables. For information about the structure of the unwind tables,
 * see "Exception Handling ABI for the ARM Architecture" at:
 *
 * http://infocenter.arm.com/help/topic/com.arm.doc.subset.swdev.abi/index.html
 */

#ifndef __CHECKER__
#if !defined (__ARM_EABI__)
#warning Your compiler does not have EABI support.
#warning    ARM unwind is known to compile only with EABI compilers.
#warning    Change compiler or disable ARM_UNWIND option.
#elif (__GNUC__ == 4 && __GNUC_MINOR__ <= 2)
#warning Your compiler is too buggy; it is known to not compile ARM unwind support.
#warning    Change compiler or disable ARM_UNWIND option.
#endif
#endif /* __CHECKER__ */

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/export.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/list.h>

#include <asm/stacktrace.h>
#include <asm/traps.h>
#include <asm/unwind.h>

/* Dummy functions to avoid linker complaints */
void __aeabi_unwind_cpp_pr0(void)
{
};
EXPORT_SYMBOL(__aeabi_unwind_cpp_pr0);

void __aeabi_unwind_cpp_pr1(void)
{
};
EXPORT_SYMBOL(__aeabi_unwind_cpp_pr1);

void __aeabi_unwind_cpp_pr2(void)
{
};
EXPORT_SYMBOL(__aeabi_unwind_cpp_pr2);

struct unwind_ctrl_block {
    unsigned long vrs[16];      /* virtual register set */
    const unsigned long *insn;  /* pointer to the current instructions word */
    int entries;            /* number of entries left to interpret */
    int byte;           /* current byte number in the instructions word */
};

enum regs {
#ifdef CONFIG_THUMB2_KERNEL
    FP = 7,
#else
    FP = 11,
#endif
    SP = 13,
    LR = 14,
    PC = 15
};

extern const struct unwind_idx __start_unwind_idx[];
static const struct unwind_idx *__origin_unwind_idx;
extern const struct unwind_idx __stop_unwind_idx[];

static DEFINE_SPINLOCK(unwind_lock);
static LIST_HEAD(unwind_tables);

/* Convert a prel31 symbol to an absolute address */
#define prel31_to_addr(ptr)             \
({                          \
    /* sign-extend to 32 bits */            \
    long offset = (((long)*(ptr)) << 1) >> 1;   \
    (unsigned long)(ptr) + offset;          \
})

/*
 * Binary search in the unwind index. The entries are
 * guaranteed to be sorted in ascending order by the linker.
 *
 * start = first entry
 * origin = first entry with positive offset (or stop if there is no such entry)
 * stop - 1 = last entry
 */
static const struct unwind_idx *search_index(unsigned long addr,
                       const struct unwind_idx *start,
                       const struct unwind_idx *origin,
                       const struct unwind_idx *stop)
{
    unsigned long addr_prel31;

    pr_debug("%s(%08lx, %p, %p, %p)\n",
            __func__, addr, start, origin, stop);

    /*
     * only search in the section with the matching sign. This way the
     * prel31 numbers can be compared as unsigned longs.
     */
    if (addr < (unsigned long)start)
        /* negative offsets: [start; origin) */
        stop = origin;
    else
        /* positive offsets: [origin; stop) */
        start = origin;

    /* prel31 for address relavive to start */
    addr_prel31 = (addr - (unsigned long)start) & 0x7fffffff;

    while (start < stop - 1) {
        const struct unwind_idx *mid = start + ((stop - start) >> 1);

        /*
         * As addr_prel31 is relative to start an offset is needed to
         * make it relative to mid.
         */
        if (addr_prel31 - ((unsigned long)mid - (unsigned long)start) <
                mid->addr_offset)
            stop = mid;
        else {
            /* keep addr_prel31 relative to start */
            addr_prel31 -= ((unsigned long)mid -
                    (unsigned long)start);
            start = mid;
        }
    }

    if (likely(start->addr_offset <= addr_prel31))
        return start;
    else {
        pr_warning("unwind: Unknown symbol address %08lx\n", addr);
        return NULL;
    }
}

static const struct unwind_idx *unwind_find_origin(
        const struct unwind_idx *start, const struct unwind_idx *stop)
{
    pr_debug("%s(%p, %p)\n", __func__, start, stop);
    while (start < stop) {
        const struct unwind_idx *mid = start + ((stop - start) >> 1);

        if (mid->addr_offset >= 0x40000000)
            /* negative offset */
            start = mid + 1;
        else
            /* positive offset */
            stop = mid;
    }
    pr_debug("%s -> %p\n", __func__, stop);
    return stop;
}

static const struct unwind_idx *unwind_find_idx(unsigned long addr)
{
    const struct unwind_idx *idx = NULL;
    unsigned long flags;

    pr_debug("%s(%08lx)\n", __func__, addr);

    if (core_kernel_text(addr)) {
        if (unlikely(!__origin_unwind_idx))
            __origin_unwind_idx =
                unwind_find_origin(__start_unwind_idx,
                        __stop_unwind_idx);

        /* main unwind table */
        idx = search_index(addr, __start_unwind_idx,
                   __origin_unwind_idx,
                   __stop_unwind_idx);
    } else {
        /* module unwind tables */
        struct unwind_table *table;

        spin_lock_irqsave(&unwind_lock, flags);
        list_for_each_entry(table, &unwind_tables, list) {
            if (addr >= table->begin_addr &&
                addr < table->end_addr) {
                idx = search_index(addr, table->start,
                           table->origin,
                           table->stop);
                /* Move-to-front to exploit common traces */
                list_move(&table->list, &unwind_tables);
                break;
            }
        }
        spin_unlock_irqrestore(&unwind_lock, flags);
    }

    pr_debug("%s: idx = %p\n", __func__, idx);
    return idx;
}

static unsigned long unwind_get_byte(struct unwind_ctrl_block *ctrl)
{
    unsigned long ret;

    if (ctrl->entries <= 0) {
        pr_warning("unwind: Corrupt unwind table\n");
        return 0;
    }

    ret = (*ctrl->insn >> (ctrl->byte * 8)) & 0xff;

    if (ctrl->byte == 0) {
        ctrl->insn++;
        ctrl->entries--;
        ctrl->byte = 3;
    } else
        ctrl->byte--;

    return ret;
}

/*
 * Execute the current unwind instruction.
 */
static int unwind_exec_insn(struct unwind_ctrl_block *ctrl)
{
    unsigned long insn = unwind_get_byte(ctrl);

    pr_debug("%s: insn = %08lx\n", __func__, insn);

    if ((insn & 0xc0) == 0x00)
        ctrl->vrs[SP] += ((insn & 0x3f) << 2) + 4;
    else if ((insn & 0xc0) == 0x40)
        ctrl->vrs[SP] -= ((insn & 0x3f) << 2) + 4;
    else if ((insn & 0xf0) == 0x80) {
        unsigned long mask;
        unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
        int load_sp, reg = 4;

        insn = (insn << 8) | unwind_get_byte(ctrl);
        mask = insn & 0x0fff;
        if (mask == 0) {
            pr_warning("unwind: 'Refuse to unwind' instruction %04lx\n",
                   insn);
            return -URC_FAILURE;
        }

        /* pop R4-R15 according to mask */
        load_sp = mask & (1 << (13 - 4));
        while (mask) {
            if (mask & 1)
                ctrl->vrs[reg] = *vsp++;
            mask >>= 1;
            reg++;
        }
        if (!load_sp)
            ctrl->vrs[SP] = (unsigned long)vsp;
    } else if ((insn & 0xf0) == 0x90 &&
           (insn & 0x0d) != 0x0d)
        ctrl->vrs[SP] = ctrl->vrs[insn & 0x0f];
    else if ((insn & 0xf0) == 0xa0) {
        unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
        int reg;

        /* pop R4-R[4+bbb] */
        for (reg = 4; reg <= 4 + (insn & 7); reg++)
            ctrl->vrs[reg] = *vsp++;
        if (insn & 0x80)
            ctrl->vrs[14] = *vsp++;
        ctrl->vrs[SP] = (unsigned long)vsp;
    } else if (insn == 0xb0) {
        if (ctrl->vrs[PC] == 0)
            ctrl->vrs[PC] = ctrl->vrs[LR];
        /* no further processing */
        ctrl->entries = 0;
    } else if (insn == 0xb1) {
        unsigned long mask = unwind_get_byte(ctrl);
        unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
        int reg = 0;

        if (mask == 0 || mask & 0xf0) {
            pr_warning("unwind: Spare encoding %04lx\n",
                   (insn << 8) | mask);
            return -URC_FAILURE;
        }

        /* pop R0-R3 according to mask */
        while (mask) {
            if (mask & 1)
                ctrl->vrs[reg] = *vsp++;
            mask >>= 1;
            reg++;
        }
        ctrl->vrs[SP] = (unsigned long)vsp;
    } else if (insn == 0xb2) {
        unsigned long uleb128 = unwind_get_byte(ctrl);

        ctrl->vrs[SP] += 0x204 + (uleb128 << 2);
    } else {
        pr_warning("unwind: Unhandled instruction %02lx\n", insn);
        return -URC_FAILURE;
    }

    pr_debug("%s: fp = %08lx sp = %08lx lr = %08lx pc = %08lx\n", __func__,
         ctrl->vrs[FP], ctrl->vrs[SP], ctrl->vrs[LR], ctrl->vrs[PC]);

    return URC_OK;
}

/*
 * Unwind a single frame starting with *sp for the symbol at *pc. It
 * updates the *pc and *sp with the new values.
 */
int unwind_frame(struct stackframe *frame)
{
    unsigned long high, low;
    const struct unwind_idx *idx;
    struct unwind_ctrl_block ctrl;

    /* only go to a higher address on the stack */
    low = frame->sp;
    high = ALIGN(low, THREAD_SIZE);

    pr_debug("%s(pc = %08lx lr = %08lx sp = %08lx)\n", __func__,
         frame->pc, frame->lr, frame->sp);

    if (!kernel_text_address(frame->pc))
        return -URC_FAILURE;

    idx = unwind_find_idx(frame->pc);
    if (!idx) {
        pr_warning("unwind: Index not found %08lx\n", frame->pc);
        return -URC_FAILURE;
    }

    ctrl.vrs[FP] = frame->fp;
    ctrl.vrs[SP] = frame->sp;
    ctrl.vrs[LR] = frame->lr;
    ctrl.vrs[PC] = 0;

    if (idx->insn == 1)
        /* can't unwind */
        return -URC_FAILURE;
    else if ((idx->insn & 0x80000000) == 0)
        /* prel31 to the unwind table */
        ctrl.insn = (unsigned long *)prel31_to_addr(&idx->insn);
    else if ((idx->insn & 0xff000000) == 0x80000000)
        /* only personality routine 0 supported in the index */
        ctrl.insn = &idx->insn;
    else {
        pr_warning("unwind: Unsupported personality routine %08lx in the index at %p\n",
               idx->insn, idx);
        return -URC_FAILURE;
    }

    /* check the personality routine */
    if ((*ctrl.insn & 0xff000000) == 0x80000000) {
        ctrl.byte = 2;
        ctrl.entries = 1;
    } else if ((*ctrl.insn & 0xff000000) == 0x81000000) {
        ctrl.byte = 1;
        ctrl.entries = 1 + ((*ctrl.insn & 0x00ff0000) >> 16);
    } else {
        pr_warning("unwind: Unsupported personality routine %08lx at %p\n",
               *ctrl.insn, ctrl.insn);
        return -URC_FAILURE;
    }

    while (ctrl.entries > 0) {
        int urc = unwind_exec_insn(&ctrl);
        if (urc < 0)
            return urc;
        if (ctrl.vrs[SP] < low || ctrl.vrs[SP] >= high)
            return -URC_FAILURE;
    }

    if (ctrl.vrs[PC] == 0)
        ctrl.vrs[PC] = ctrl.vrs[LR];

    /* check for infinite loop */
    if (frame->pc == ctrl.vrs[PC])
        return -URC_FAILURE;

    frame->fp = ctrl.vrs[FP];
    frame->sp = ctrl.vrs[SP];
    frame->lr = ctrl.vrs[LR];
    frame->pc = ctrl.vrs[PC];

    return URC_OK;
}

void unwind_backtrace(struct pt_regs *regs, struct task_struct *tsk)
{
    struct stackframe frame;
    register unsigned long current_sp asm ("sp");

    pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);

    if (!tsk)
        tsk = current;

    if (regs) {
        frame.fp = regs->ARM_fp;
        frame.sp = regs->ARM_sp;
        frame.lr = regs->ARM_lr;
        /* PC might be corrupted, use LR in that case. */
        frame.pc = kernel_text_address(regs->ARM_pc)
             ? regs->ARM_pc : regs->ARM_lr;
    } else if (tsk == current) {
        frame.fp = (unsigned long)__builtin_frame_address(0);
        frame.sp = current_sp;
        frame.lr = (unsigned long)__builtin_return_address(0);
        frame.pc = (unsigned long)unwind_backtrace;
    } else {
        /* task blocked in __switch_to */
        frame.fp = thread_saved_fp(tsk);
        frame.sp = thread_saved_sp(tsk);
        /*
         * The function calling __switch_to cannot be a leaf function
         * so LR is recovered from the stack.
         */
        frame.lr = 0;
        frame.pc = thread_saved_pc(tsk);
    }

    while (1) {
        int urc;
        unsigned long where = frame.pc;

        urc = unwind_frame(&frame);
        if (urc < 0)
            break;
        dump_backtrace_entry(where, frame.pc, frame.sp - 4);
    }
}

struct unwind_table *unwind_table_add(unsigned long start, unsigned long size,
                      unsigned long text_addr,
                      unsigned long text_size)
{
    unsigned long flags;
    struct unwind_table *tab = kmalloc(sizeof(*tab), GFP_KERNEL);

    pr_debug("%s(%08lx, %08lx, %08lx, %08lx)\n", __func__, start, size,
         text_addr, text_size);

    if (!tab)
        return tab;

    tab->start = (const struct unwind_idx *)start;
    tab->stop = (const struct unwind_idx *)(start + size);
    tab->origin = unwind_find_origin(tab->start, tab->stop);
    tab->begin_addr = text_addr;
    tab->end_addr = text_addr + text_size;

    spin_lock_irqsave(&unwind_lock, flags);
    list_add_tail(&tab->list, &unwind_tables);
    spin_unlock_irqrestore(&unwind_lock, flags);

    return tab;
}

void unwind_table_del(struct unwind_table *tab)
{
    unsigned long flags;

    if (!tab)
        return;

    spin_lock_irqsave(&unwind_lock, flags);
    list_del(&tab->list);
    spin_unlock_irqrestore(&unwind_lock, flags);

    kfree(tab);
}