/*
 * 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) && !defined(__clang__)
#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 */
        unsigned long sp_high;          /* highest value of sp allowed */
        /*
         * 1 : check for stack overflow for each register pop.
         * 0 : save overhead if there is plenty of stack remaining.
         */
        int check_each_pop;
        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_warn("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_warn("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;
}

/* Before poping a register check whether it is feasible or not */
static int unwind_pop_register(struct unwind_ctrl_block *ctrl,
                                unsigned long **vsp, unsigned int reg)
{
        if (unlikely(ctrl->check_each_pop))
                if (*vsp >= (unsigned long *)ctrl->sp_high)
                        return -URC_FAILURE;

        ctrl->vrs[reg] = *(*vsp)++;
        return URC_OK;
}

/* Helper functions to execute the instructions */
static int unwind_exec_pop_subset_r4_to_r13(struct unwind_ctrl_block *ctrl,
                                                unsigned long mask)
{
        unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
        int load_sp, reg = 4;

        load_sp = mask & (1 << (13 - 4));
        while (mask) {
                if (mask & 1)
                        if (unwind_pop_register(ctrl, &vsp, reg))
                                return -URC_FAILURE;
                mask >>= 1;
                reg++;
        }
        if (!load_sp)
                ctrl->vrs[SP] = (unsigned long)vsp;

        return URC_OK;
}

static int unwind_exec_pop_r4_to_rN(struct unwind_ctrl_block *ctrl,
                                        unsigned long insn)
{
        unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
        int reg;

        /* pop R4-R[4+bbb] */
        for (reg = 4; reg <= 4 + (insn & 7); reg++)
                if (unwind_pop_register(ctrl, &vsp, reg))
                                return -URC_FAILURE;

        if (insn & 0x8)
                if (unwind_pop_register(ctrl, &vsp, 14))
                                return -URC_FAILURE;

        ctrl->vrs[SP] = (unsigned long)vsp;

        return URC_OK;
}

static int unwind_exec_pop_subset_r0_to_r3(struct unwind_ctrl_block *ctrl,
                                                unsigned long mask)
{
        unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
        int reg = 0;

        /* pop R0-R3 according to mask */
        while (mask) {
                if (mask & 1)
                        if (unwind_pop_register(ctrl, &vsp, reg))
                                return -URC_FAILURE;
                mask >>= 1;
                reg++;
        }
        ctrl->vrs[SP] = (unsigned long)vsp;

        return URC_OK;
}

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

        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;

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

                ret = unwind_exec_pop_subset_r4_to_r13(ctrl, mask);
                if (ret)
                        goto error;
        } else if ((insn & 0xf0) == 0x90 &&
                   (insn & 0x0d) != 0x0d)
                ctrl->vrs[SP] = ctrl->vrs[insn & 0x0f];
        else if ((insn & 0xf0) == 0xa0) {
                ret = unwind_exec_pop_r4_to_rN(ctrl, insn);
                if (ret)
                        goto error;
        } 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);

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

                ret = unwind_exec_pop_subset_r0_to_r3(ctrl, mask);
                if (ret)
                        goto error;
        } else if (insn == 0xb2) {
                unsigned long uleb128 = unwind_get_byte(ctrl);

                ctrl->vrs[SP] += 0x204 + (uleb128 << 2);
        } else {
                pr_warn("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]);

error:
        return ret;
}

/*
 * 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 low;
        const struct unwind_idx *idx;
        struct unwind_ctrl_block ctrl;

        /* store the highest address on the stack to avoid crossing it*/
        low = frame->sp;
        ctrl.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_warn("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_warn("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_warn("unwind: Unsupported personality routine %08lx at %p\n",
                        *ctrl.insn, ctrl.insn);
                return -URC_FAILURE;
        }

        ctrl.check_each_pop = 0;

        while (ctrl.entries > 0) {
                int urc;
                if ((ctrl.sp_high - ctrl.vrs[SP]) < sizeof(ctrl.vrs))
                        ctrl.check_each_pop = 1;
                urc = unwind_exec_insn(&ctrl);
                if (urc < 0)
                        return urc;
                if (ctrl.vrs[SP] < low || ctrl.vrs[SP] >= ctrl.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;

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

        if (!tsk)
                tsk = current;

        if (regs) {
                arm_get_current_stackframe(regs, &frame);
                /* PC might be corrupted, use LR in that case. */
                if (!kernel_text_address(regs->ARM_pc))
                        frame.pc = regs->ARM_lr;
        } else if (tsk == current) {
                frame.fp = (unsigned long)__builtin_frame_address(0);
                frame.sp = current_stack_pointer;
                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);
}