/*
 * Kernel and userspace stack tracing.
 *
 * 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) 2001 - 2013 Tensilica Inc.
 * Copyright (C) 2015 Cadence Design Systems Inc.
 */
#include <linux/export.h>
#include <linux/sched.h>
#include <linux/stacktrace.h>

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

#if IS_ENABLED(CONFIG_OPROFILE) || IS_ENABLED(CONFIG_PERF_EVENTS)

/* Address of common_exception_return, used to check the
 * transition from kernel to user space.
 */
extern int common_exception_return;

/* A struct that maps to the part of the frame containing the a0 and
 * a1 registers.
 */
struct frame_start {
        unsigned long a0;
        unsigned long a1;
};

void xtensa_backtrace_user(struct pt_regs *regs, unsigned int depth,
                           int (*ufn)(struct stackframe *frame, void *data),
                           void *data)
{
        unsigned long windowstart = regs->windowstart;
        unsigned long windowbase = regs->windowbase;
        unsigned long a0 = regs->areg[0];
        unsigned long a1 = regs->areg[1];
        unsigned long pc = regs->pc;
        struct stackframe frame;
        int index;

        if (!depth--)
                return;

        frame.pc = pc;
        frame.sp = a1;

        if (pc == 0 || pc >= TASK_SIZE || ufn(&frame, data))
                return;

        /* Two steps:
         *
         * 1. Look through the register window for the
         * previous PCs in the call trace.
         *
         * 2. Look on the stack.
         */

        /* Step 1.  */
        /* Rotate WINDOWSTART to move the bit corresponding to
         * the current window to the bit #0.
         */
        windowstart = (windowstart << WSBITS | windowstart) >> windowbase;

        /* Look for bits that are set, they correspond to
         * valid windows.
         */
        for (index = WSBITS - 1; (index > 0) && depth; depth--, index--)
                if (windowstart & (1 << index)) {
                        /* Get the PC from a0 and a1. */
                        pc = MAKE_PC_FROM_RA(a0, pc);
                        /* Read a0 and a1 from the
                         * corresponding position in AREGs.
                         */
                        a0 = regs->areg[index * 4];
                        a1 = regs->areg[index * 4 + 1];

                        frame.pc = pc;
                        frame.sp = a1;

                        if (pc == 0 || pc >= TASK_SIZE || ufn(&frame, data))
                                return;
                }

        /* Step 2. */
        /* We are done with the register window, we need to
         * look through the stack.
         */
        if (!depth)
                return;

        /* Start from the a1 register. */
        /* a1 = regs->areg[1]; */
        while (a0 != 0 && depth--) {
                struct frame_start frame_start;
                /* Get the location for a1, a0 for the
                 * previous frame from the current a1.
                 */
                unsigned long *psp = (unsigned long *)a1;

                psp -= 4;

                /* Check if the region is OK to access. */
                if (!access_ok(VERIFY_READ, psp, sizeof(frame_start)))
                        return;
                /* Copy a1, a0 from user space stack frame. */
                if (__copy_from_user_inatomic(&frame_start, psp,
                                              sizeof(frame_start)))
                        return;

                pc = MAKE_PC_FROM_RA(a0, pc);
                a0 = frame_start.a0;
                a1 = frame_start.a1;

                frame.pc = pc;
                frame.sp = a1;

                if (pc == 0 || pc >= TASK_SIZE || ufn(&frame, data))
                        return;
        }
}
EXPORT_SYMBOL(xtensa_backtrace_user);

void xtensa_backtrace_kernel(struct pt_regs *regs, unsigned int depth,
                             int (*kfn)(struct stackframe *frame, void *data),
                             int (*ufn)(struct stackframe *frame, void *data),
                             void *data)
{
        unsigned long pc = regs->depc > VALID_DOUBLE_EXCEPTION_ADDRESS ?
                regs->depc : regs->pc;
        unsigned long sp_start, sp_end;
        unsigned long a0 = regs->areg[0];
        unsigned long a1 = regs->areg[1];

        sp_start = a1 & ~(THREAD_SIZE - 1);
        sp_end = sp_start + THREAD_SIZE;

        /* Spill the register window to the stack first. */
        spill_registers();

        /* Read the stack frames one by one and create the PC
         * from the a0 and a1 registers saved there.
         */
        while (a1 > sp_start && a1 < sp_end && depth--) {
                struct stackframe frame;
                unsigned long *psp = (unsigned long *)a1;

                frame.pc = pc;
                frame.sp = a1;

                if (kernel_text_address(pc) && kfn(&frame, data))
                        return;

                if (pc == (unsigned long)&common_exception_return) {
                        regs = (struct pt_regs *)a1;
                        if (user_mode(regs)) {
                                if (ufn == NULL)
                                        return;
                                xtensa_backtrace_user(regs, depth, ufn, data);
                                return;
                        }
                        a0 = regs->areg[0];
                        a1 = regs->areg[1];
                        continue;
                }

                sp_start = a1;

                pc = MAKE_PC_FROM_RA(a0, pc);
                a0 = *(psp - 4);
                a1 = *(psp - 3);
        }
}
EXPORT_SYMBOL(xtensa_backtrace_kernel);

#endif

void walk_stackframe(unsigned long *sp,
                int (*fn)(struct stackframe *frame, void *data),
                void *data)
{
        unsigned long a0, a1;
        unsigned long sp_end;

        a1 = (unsigned long)sp;
        sp_end = ALIGN(a1, THREAD_SIZE);

        spill_registers();

        while (a1 < sp_end) {
                struct stackframe frame;

                sp = (unsigned long *)a1;

                a0 = *(sp - 4);
                a1 = *(sp - 3);

                if (a1 <= (unsigned long)sp)
                        break;

                frame.pc = MAKE_PC_FROM_RA(a0, a1);
                frame.sp = a1;

                if (fn(&frame, data))
                        return;
        }
}

#ifdef CONFIG_STACKTRACE

struct stack_trace_data {
        struct stack_trace *trace;
        unsigned skip;
};

static int stack_trace_cb(struct stackframe *frame, void *data)
{
        struct stack_trace_data *trace_data = data;
        struct stack_trace *trace = trace_data->trace;

        if (trace_data->skip) {
                --trace_data->skip;
                return 0;
        }
        if (!kernel_text_address(frame->pc))
                return 0;

        trace->entries[trace->nr_entries++] = frame->pc;
        return trace->nr_entries >= trace->max_entries;
}

void save_stack_trace_tsk(struct task_struct *task, struct stack_trace *trace)
{
        struct stack_trace_data trace_data = {
                .trace = trace,
                .skip = trace->skip,
        };
        walk_stackframe(stack_pointer(task), stack_trace_cb, &trace_data);
}
EXPORT_SYMBOL_GPL(save_stack_trace_tsk);

void save_stack_trace(struct stack_trace *trace)
{
        save_stack_trace_tsk(current, trace);
}
EXPORT_SYMBOL_GPL(save_stack_trace);

#endif

#ifdef CONFIG_FRAME_POINTER

struct return_addr_data {
        unsigned long addr;
        unsigned skip;
};

static int return_address_cb(struct stackframe *frame, void *data)
{
        struct return_addr_data *r = data;

        if (r->skip) {
                --r->skip;
                return 0;
        }
        if (!kernel_text_address(frame->pc))
                return 0;
        r->addr = frame->pc;
        return 1;
}

unsigned long return_address(unsigned level)
{
        struct return_addr_data r = {
                .skip = level + 1,
        };
        walk_stackframe(stack_pointer(NULL), return_address_cb, &r);
        return r.addr;
}
EXPORT_SYMBOL(return_address);

#endif