/*
 * Dynamic function tracing support.
 *
 * Copyright (C) 2008 Abhishek Sagar <sagar.abhishek@gmail.com>
 * Copyright (C) 2010 Rabin Vincent <rabin@rab.in>
 *
 * For licencing details, see COPYING.
 *
 * Defines low-level handling of mcount calls when the kernel
 * is compiled with the -pg flag. When using dynamic ftrace, the
 * mcount call-sites get patched with NOP till they are enabled.
 * All code mutation routines here are called under stop_machine().
 */

#include <linux/ftrace.h>
#include <linux/uaccess.h>

#include <asm/cacheflush.h>
#include <asm/ftrace.h>

#ifdef CONFIG_THUMB2_KERNEL
#define NOP             0xeb04f85d      /* pop.w {lr} */
#else
#define NOP             0xe8bd4000      /* pop {lr} */
#endif

#ifdef CONFIG_DYNAMIC_FTRACE
#ifdef CONFIG_OLD_MCOUNT
#define OLD_MCOUNT_ADDR ((unsigned long) mcount)
#define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)

#define OLD_NOP         0xe1a00000      /* mov r0, r0 */

static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
{
        return rec->arch.old_mcount ? OLD_NOP : NOP;
}

static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
{
        if (!rec->arch.old_mcount)
                return addr;

        if (addr == MCOUNT_ADDR)
                addr = OLD_MCOUNT_ADDR;
        else if (addr == FTRACE_ADDR)
                addr = OLD_FTRACE_ADDR;

        return addr;
}
#else
static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
{
        return NOP;
}

static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
{
        return addr;
}
#endif

#ifdef CONFIG_THUMB2_KERNEL
static unsigned long ftrace_gen_branch(unsigned long pc, unsigned long addr,
                                       bool link)
{
        unsigned long s, j1, j2, i1, i2, imm10, imm11;
        unsigned long first, second;
        long offset;

        offset = (long)addr - (long)(pc + 4);
        if (offset < -16777216 || offset > 16777214) {
                WARN_ON_ONCE(1);
                return 0;
        }

        s       = (offset >> 24) & 0x1;
        i1      = (offset >> 23) & 0x1;
        i2      = (offset >> 22) & 0x1;
        imm10   = (offset >> 12) & 0x3ff;
        imm11   = (offset >>  1) & 0x7ff;

        j1 = (!i1) ^ s;
        j2 = (!i2) ^ s;

        first = 0xf000 | (s << 10) | imm10;
        second = 0x9000 | (j1 << 13) | (j2 << 11) | imm11;
        if (link)
                second |= 1 << 14;

        return (second << 16) | first;
}
#else
static unsigned long ftrace_gen_branch(unsigned long pc, unsigned long addr,
                                       bool link)
{
        unsigned long opcode = 0xea000000;
        long offset;

        if (link)
                opcode |= 1 << 24;

        offset = (long)addr - (long)(pc + 8);
        if (unlikely(offset < -33554432 || offset > 33554428)) {
                /* Can't generate branches that far (from ARM ARM). Ftrace
                 * doesn't generate branches outside of kernel text.
                 */
                WARN_ON_ONCE(1);
                return 0;
        }

        offset = (offset >> 2) & 0x00ffffff;

        return opcode | offset;
}
#endif

static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
{
        return ftrace_gen_branch(pc, addr, true);
}

static int ftrace_modify_code(unsigned long pc, unsigned long old,
                              unsigned long new)
{
        unsigned long replaced;

        if (probe_kernel_read(&replaced, (void *)pc, MCOUNT_INSN_SIZE))
                return -EFAULT;

        if (replaced != old)
                return -EINVAL;

        if (probe_kernel_write((void *)pc, &new, MCOUNT_INSN_SIZE))
                return -EPERM;

        flush_icache_range(pc, pc + MCOUNT_INSN_SIZE);

        return 0;
}

int ftrace_update_ftrace_func(ftrace_func_t func)
{
        unsigned long pc, old;
        unsigned long new;
        int ret;

        pc = (unsigned long)&ftrace_call;
        memcpy(&old, &ftrace_call, MCOUNT_INSN_SIZE);
        new = ftrace_call_replace(pc, (unsigned long)func);

        ret = ftrace_modify_code(pc, old, new);

#ifdef CONFIG_OLD_MCOUNT
        if (!ret) {
                pc = (unsigned long)&ftrace_call_old;
                memcpy(&old, &ftrace_call_old, MCOUNT_INSN_SIZE);
                new = ftrace_call_replace(pc, (unsigned long)func);

                ret = ftrace_modify_code(pc, old, new);
        }
#endif

        return ret;
}

int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
        unsigned long new, old;
        unsigned long ip = rec->ip;

        old = ftrace_nop_replace(rec);
        new = ftrace_call_replace(ip, adjust_address(rec, addr));

        return ftrace_modify_code(rec->ip, old, new);
}

int ftrace_make_nop(struct module *mod,
                    struct dyn_ftrace *rec, unsigned long addr)
{
        unsigned long ip = rec->ip;
        unsigned long old;
        unsigned long new;
        int ret;

        old = ftrace_call_replace(ip, adjust_address(rec, addr));
        new = ftrace_nop_replace(rec);
        ret = ftrace_modify_code(ip, old, new);

#ifdef CONFIG_OLD_MCOUNT
        if (ret == -EINVAL && addr == MCOUNT_ADDR) {
                rec->arch.old_mcount = true;

                old = ftrace_call_replace(ip, adjust_address(rec, addr));
                new = ftrace_nop_replace(rec);
                ret = ftrace_modify_code(ip, old, new);
        }
#endif

        return ret;
}

int __init ftrace_dyn_arch_init(void *data)
{
        *(unsigned long *)data = 0;

        return 0;
}
#endif /* CONFIG_DYNAMIC_FTRACE */

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
                           unsigned long frame_pointer)
{
        unsigned long return_hooker = (unsigned long) &return_to_handler;
        struct ftrace_graph_ent trace;
        unsigned long old;
        int err;

        if (unlikely(atomic_read(&current->tracing_graph_pause)))
                return;

        old = *parent;
        *parent = return_hooker;

        err = ftrace_push_return_trace(old, self_addr, &trace.depth,
                                       frame_pointer);
        if (err == -EBUSY) {
                *parent = old;
                return;
        }

        trace.func = self_addr;

        /* Only trace if the calling function expects to */
        if (!ftrace_graph_entry(&trace)) {
                current->curr_ret_stack--;
                *parent = old;
        }
}

#ifdef CONFIG_DYNAMIC_FTRACE
extern unsigned long ftrace_graph_call;
extern unsigned long ftrace_graph_call_old;
extern void ftrace_graph_caller_old(void);

static int __ftrace_modify_caller(unsigned long *callsite,
                                  void (*func) (void), bool enable)
{
        unsigned long caller_fn = (unsigned long) func;
        unsigned long pc = (unsigned long) callsite;
        unsigned long branch = ftrace_gen_branch(pc, caller_fn, false);
        unsigned long nop = 0xe1a00000; /* mov r0, r0 */
        unsigned long old = enable ? nop : branch;
        unsigned long new = enable ? branch : nop;

        return ftrace_modify_code(pc, old, new);
}

static int ftrace_modify_graph_caller(bool enable)
{
        int ret;

        ret = __ftrace_modify_caller(&ftrace_graph_call,
                                     ftrace_graph_caller,
                                     enable);

#ifdef CONFIG_OLD_MCOUNT
        if (!ret)
                ret = __ftrace_modify_caller(&ftrace_graph_call_old,
                                             ftrace_graph_caller_old,
                                             enable);
#endif

        return ret;
}

int ftrace_enable_ftrace_graph_caller(void)
{
        return ftrace_modify_graph_caller(true);
}

int ftrace_disable_ftrace_graph_caller(void)
{
        return ftrace_modify_graph_caller(false);
}
#endif /* CONFIG_DYNAMIC_FTRACE */
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */