ftrace.c

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/*
 * Dynamic function tracing support.
 *
 * Copyright (C) 2008 Shaohua Li <[email protected]>
 *
 * 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 lazily with NOP till they are
 * enabled. All code mutation routines here take effect atomically.
 */

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

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

/* In IA64, each function will be added below two bundles with -pg option */
static unsigned char __attribute__((aligned(8)))
ftrace_orig_code[MCOUNT_INSN_SIZE] = {
    0x02, 0x40, 0x31, 0x10, 0x80, 0x05, /* alloc r40=ar.pfs,12,8,0 */
    0xb0, 0x02, 0x00, 0x00, 0x42, 0x40, /* mov r43=r0;; */
    0x05, 0x00, 0xc4, 0x00,             /* mov r42=b0 */
    0x11, 0x48, 0x01, 0x02, 0x00, 0x21, /* mov r41=r1 */
    0x00, 0x00, 0x00, 0x02, 0x00, 0x00, /* nop.i 0x0 */
    0x08, 0x00, 0x00, 0x50              /* br.call.sptk.many b0 = _mcount;; */
};

struct ftrace_orig_insn {
    u64 dummy1, dummy2, dummy3;
    u64 dummy4:64-41+13;
    u64 imm20:20;
    u64 dummy5:3;
    u64 sign:1;
    u64 dummy6:4;
};

/* mcount stub will be converted below for nop */
static unsigned char ftrace_nop_code[MCOUNT_INSN_SIZE] = {
    0x00, 0x00, 0x00, 0x00, 0x01, 0x00, /* [MII] nop.m 0x0 */
    0x30, 0x00, 0x00, 0x60, 0x00, 0x00, /* mov r3=ip */
    0x00, 0x00, 0x04, 0x00,             /* nop.i 0x0 */
    0x05, 0x00, 0x00, 0x00, 0x01, 0x00, /* [MLX] nop.m 0x0 */
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /* nop.x 0x0;; */
    0x00, 0x00, 0x04, 0x00
};

static unsigned char *ftrace_nop_replace(void)
{
    return ftrace_nop_code;
}

/*
 * mcount stub will be converted below for call
 * Note: Just the last instruction is changed against nop
 * */
static unsigned char __attribute__((aligned(8)))
ftrace_call_code[MCOUNT_INSN_SIZE] = {
    0x00, 0x00, 0x00, 0x00, 0x01, 0x00, /* [MII] nop.m 0x0 */
    0x30, 0x00, 0x00, 0x60, 0x00, 0x00, /* mov r3=ip */
    0x00, 0x00, 0x04, 0x00,             /* nop.i 0x0 */
    0x05, 0x00, 0x00, 0x00, 0x01, 0x00, /* [MLX] nop.m 0x0 */
    0xff, 0xff, 0xff, 0xff, 0x7f, 0x00, /* brl.many .;;*/
    0xf8, 0xff, 0xff, 0xc8
};

struct ftrace_call_insn {
    u64 dummy1, dummy2;
    u64 dummy3:48;
    u64 imm39_l:16;
    u64 imm39_h:23;
    u64 dummy4:13;
    u64 imm20:20;
    u64 dummy5:3;
    u64 i:1;
    u64 dummy6:4;
};

static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
{
    struct ftrace_call_insn *code = (void *)ftrace_call_code;
    unsigned long offset = addr - (ip + 0x10);

    code->imm39_l = offset >> 24;
    code->imm39_h = offset >> 40;
    code->imm20 = offset >> 4;
    code->i = offset >> 63;
    return ftrace_call_code;
}

static int
ftrace_modify_code(unsigned long ip, unsigned char *old_code,
           unsigned char *new_code, int do_check)
{
    unsigned char replaced[MCOUNT_INSN_SIZE];

    /*
     * Note: Due to modules and __init, code can
     *  disappear and change, we need to protect against faulting
     *  as well as code changing. We do this by using the
     *  probe_kernel_* functions.
     *
     * No real locking needed, this code is run through
     * kstop_machine, or before SMP starts.
     */

    if (!do_check)
        goto skip_check;

    /* read the text we want to modify */
    if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
        return -EFAULT;

    /* Make sure it is what we expect it to be */
    if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
        return -EINVAL;

skip_check:
    /* replace the text with the new text */
    if (probe_kernel_write(((void *)ip), new_code, MCOUNT_INSN_SIZE))
        return -EPERM;
    flush_icache_range(ip, ip + MCOUNT_INSN_SIZE);

    return 0;
}

static int ftrace_make_nop_check(struct dyn_ftrace *rec, unsigned long addr)
{
    unsigned char __attribute__((aligned(8))) replaced[MCOUNT_INSN_SIZE];
    unsigned long ip = rec->ip;

    if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
        return -EFAULT;
    if (rec->flags & FTRACE_FL_CONVERTED) {
        struct ftrace_call_insn *call_insn, *tmp_call;

        call_insn = (void *)ftrace_call_code;
        tmp_call = (void *)replaced;
        call_insn->imm39_l = tmp_call->imm39_l;
        call_insn->imm39_h = tmp_call->imm39_h;
        call_insn->imm20 = tmp_call->imm20;
        call_insn->i = tmp_call->i;
        if (memcmp(replaced, ftrace_call_code, MCOUNT_INSN_SIZE) != 0)
            return -EINVAL;
        return 0;
    } else {
        struct ftrace_orig_insn *call_insn, *tmp_call;

        call_insn = (void *)ftrace_orig_code;
        tmp_call = (void *)replaced;
        call_insn->sign = tmp_call->sign;
        call_insn->imm20 = tmp_call->imm20;
        if (memcmp(replaced, ftrace_orig_code, MCOUNT_INSN_SIZE) != 0)
            return -EINVAL;
        return 0;
    }
}

int ftrace_make_nop(struct module *mod,
            struct dyn_ftrace *rec, unsigned long addr)
{
    int ret;
    char *new;

    ret = ftrace_make_nop_check(rec, addr);
    if (ret)
        return ret;
    new = ftrace_nop_replace();
    return ftrace_modify_code(rec->ip, NULL, new, 0);
}

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

    old=  ftrace_nop_replace();
    new = ftrace_call_replace(ip, addr);
    return ftrace_modify_code(ip, old, new, 1);
}

/* in IA64, _mcount can't directly call ftrace_stub. Only jump is ok */
int ftrace_update_ftrace_func(ftrace_func_t func)
{
    unsigned long ip;
    unsigned long addr = ((struct fnptr *)ftrace_call)->ip;

    if (func == ftrace_stub)
        return 0;
    ip = ((struct fnptr *)func)->ip;

    ia64_patch_imm64(addr + 2, ip);

    flush_icache_range(addr, addr + 16);
    return 0;
}

/* run from kstop_machine */
int __init ftrace_dyn_arch_init(void *data)
{
    *(unsigned long *)data = 0;

    return 0;
}