// SPDX-License-Identifier: GPL-2.0
/*
 * ARM callchain support
 *
 * Copyright (C) 2009 picoChip Designs, Ltd., Jamie Iles
 * Copyright (C) 2010 ARM Ltd., Will Deacon <will.deacon@arm.com>
 *
 * This code is based on the ARM OProfile backtrace code.
 */
#include <linux/perf_event.h>
#include <linux/uaccess.h>

#include <asm/stacktrace.h>

/*
 * The registers we're interested in are at the end of the variable
 * length saved register structure. The fp points at the end of this
 * structure so the address of this struct is:
 * (struct frame_tail *)(xxx->fp)-1
 *
 * This code has been adapted from the ARM OProfile support.
 */
struct frame_tail {
        struct frame_tail __user *fp;
        unsigned long sp;
        unsigned long lr;
} __attribute__((packed));

/*
 * Get the return address for a single stackframe and return a pointer to the
 * next frame tail.
 */
static struct frame_tail __user *
user_backtrace(struct frame_tail __user *tail,
               struct perf_callchain_entry_ctx *entry)
{
        struct frame_tail buftail;
        unsigned long err;

        if (!access_ok(tail, sizeof(buftail)))
                return NULL;

        pagefault_disable();
        err = __copy_from_user_inatomic(&buftail, tail, sizeof(buftail));
        pagefault_enable();

        if (err)
                return NULL;

        perf_callchain_store(entry, buftail.lr);

        /*
         * Frame pointers should strictly progress back up the stack
         * (towards higher addresses).
         */
        if (tail + 1 >= buftail.fp)
                return NULL;

        return buftail.fp - 1;
}

void
perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs)
{
        struct frame_tail __user *tail;

        perf_callchain_store(entry, regs->ARM_pc);

        if (!current->mm)
                return;

        tail = (struct frame_tail __user *)regs->ARM_fp - 1;

        while ((entry->nr < entry->max_stack) &&
               tail && !((unsigned long)tail & 0x3))
                tail = user_backtrace(tail, entry);
}

/*
 * Gets called by walk_stackframe() for every stackframe. This will be called
 * whist unwinding the stackframe and is like a subroutine return so we use
 * the PC.
 */
static bool
callchain_trace(void *data, unsigned long pc)
{
        struct perf_callchain_entry_ctx *entry = data;
        return perf_callchain_store(entry, pc) == 0;
}

void
perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs)
{
        struct stackframe fr;

        arm_get_current_stackframe(regs, &fr);
        walk_stackframe(&fr, callchain_trace, entry);
}