ftrace.c

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/*
 * Code for replacing ftrace calls with jumps.
 *
 * Copyright (C) 2007-2008 Steven Rostedt <[email protected]>
 * Copyright (C) 2009, 2010 DSLab, Lanzhou University, China
 * Author: Wu Zhangjin <[email protected]>
 *
 * Thanks goes to Steven Rostedt for writing the original x86 version.
 */

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

#include <asm/asm.h>
#include <asm/asm-offsets.h>
#include <asm/cacheflush.h>
#include <asm/uasm.h>

#include <asm-generic/sections.h>

#if defined(KBUILD_MCOUNT_RA_ADDRESS) && defined(CONFIG_32BIT)
#define MCOUNT_OFFSET_INSNS 5
#else
#define MCOUNT_OFFSET_INSNS 4
#endif

/*
 * Check if the address is in kernel space
 *
 * Clone core_kernel_text() from kernel/extable.c, but doesn't call
 * init_kernel_text() for Ftrace doesn't trace functions in init sections.
 */
static inline int in_kernel_space(unsigned long ip)
{
    if (ip >= (unsigned long)_stext &&
        ip <= (unsigned long)_etext)
        return 1;
    return 0;
}

#ifdef CONFIG_DYNAMIC_FTRACE

#define JAL 0x0c000000      /* jump & link: ip --> ra, jump to target */
#define ADDR_MASK 0x03ffffff    /*  op_code|addr : 31...26|25 ....0 */
#define JUMP_RANGE_MASK ((1UL << 28) - 1)

#define INSN_NOP 0x00000000 /* nop */
#define INSN_JAL(addr)  \
    ((unsigned int)(JAL | (((addr) >> 2) & ADDR_MASK)))

static unsigned int insn_jal_ftrace_caller __read_mostly;
static unsigned int insn_lui_v1_hi16_mcount __read_mostly;
static unsigned int insn_j_ftrace_graph_caller __maybe_unused __read_mostly;

static inline void ftrace_dyn_arch_init_insns(void)
{
    u32 *buf;
    unsigned int v1;

    /* lui v1, hi16_mcount */
    v1 = 3;
    buf = (u32 *)&insn_lui_v1_hi16_mcount;
    UASM_i_LA_mostly(&buf, v1, MCOUNT_ADDR);

    /* jal (ftrace_caller + 8), jump over the first two instruction */
    buf = (u32 *)&insn_jal_ftrace_caller;
    uasm_i_jal(&buf, (FTRACE_ADDR + 8) & JUMP_RANGE_MASK);

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
    /* j ftrace_graph_caller */
    buf = (u32 *)&insn_j_ftrace_graph_caller;
    uasm_i_j(&buf, (unsigned long)ftrace_graph_caller & JUMP_RANGE_MASK);
#endif
}

static int ftrace_modify_code(unsigned long ip, unsigned int new_code)
{
    int faulted;

    /* *(unsigned int *)ip = new_code; */
    safe_store_code(new_code, ip, faulted);

    if (unlikely(faulted))
        return -EFAULT;

    flush_icache_range(ip, ip + 8);

    return 0;
}

/*
 * The details about the calling site of mcount on MIPS
 *
 * 1. For kernel:
 *
 * move at, ra
 * jal _mcount      --> nop
 *
 * 2. For modules:
 *
 * 2.1 For KBUILD_MCOUNT_RA_ADDRESS and CONFIG_32BIT
 *
 * lui v1, hi_16bit_of_mcount        --> b 1f (0x10000005)
 * addiu v1, v1, low_16bit_of_mcount
 * move at, ra
 * move $12, ra_address
 * jalr v1
 *  sub sp, sp, 8
 *                                  1: offset = 5 instructions
 * 2.2 For the Other situations
 *
 * lui v1, hi_16bit_of_mcount        --> b 1f (0x10000004)
 * addiu v1, v1, low_16bit_of_mcount
 * move at, ra
 * jalr v1
 *  nop | move $12, ra_address | sub sp, sp, 8
 *                                  1: offset = 4 instructions
 */

#define INSN_B_1F (0x10000000 | MCOUNT_OFFSET_INSNS)

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

    /*
     * If ip is in kernel space, no long call, otherwise, long call is
     * needed.
     */
    new = in_kernel_space(ip) ? INSN_NOP : INSN_B_1F;

    return ftrace_modify_code(ip, new);
}

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

    new = in_kernel_space(ip) ? insn_jal_ftrace_caller :
        insn_lui_v1_hi16_mcount;

    return ftrace_modify_code(ip, new);
}

#define FTRACE_CALL_IP ((unsigned long)(&ftrace_call))

int ftrace_update_ftrace_func(ftrace_func_t func)
{
    unsigned int new;

    new = INSN_JAL((unsigned long)func);

    return ftrace_modify_code(FTRACE_CALL_IP, new);
}

int __init ftrace_dyn_arch_init(void *data)
{
    /* Encode the instructions when booting */
    ftrace_dyn_arch_init_insns();

    /* Remove "b ftrace_stub" to ensure ftrace_caller() is executed */
    ftrace_modify_code(MCOUNT_ADDR, INSN_NOP);

    /* The return code is retured via data */
    *(unsigned long *)data = 0;

    return 0;
}
#endif  /* CONFIG_DYNAMIC_FTRACE */

#ifdef CONFIG_FUNCTION_GRAPH_TRACER

#ifdef CONFIG_DYNAMIC_FTRACE

extern void ftrace_graph_call(void);
#define FTRACE_GRAPH_CALL_IP    ((unsigned long)(&ftrace_graph_call))

int ftrace_enable_ftrace_graph_caller(void)
{
    return ftrace_modify_code(FTRACE_GRAPH_CALL_IP,
            insn_j_ftrace_graph_caller);
}

int ftrace_disable_ftrace_graph_caller(void)
{
    return ftrace_modify_code(FTRACE_GRAPH_CALL_IP, INSN_NOP);
}

#endif  /* CONFIG_DYNAMIC_FTRACE */

#ifndef KBUILD_MCOUNT_RA_ADDRESS

#define S_RA_SP (0xafbf << 16)  /* s{d,w} ra, offset(sp) */
#define S_R_SP  (0xafb0 << 16)  /* s{d,w} R, offset(sp) */
#define OFFSET_MASK 0xffff  /* stack offset range: 0 ~ PT_SIZE */

unsigned long ftrace_get_parent_ra_addr(unsigned long self_ra, unsigned long
        old_parent_ra, unsigned long parent_ra_addr, unsigned long fp)
{
    unsigned long sp, ip, tmp;
    unsigned int code;
    int faulted;

    /*
     * For module, move the ip from the return address after the
     * instruction "lui v1, hi_16bit_of_mcount"(offset is 24), but for
     * kernel, move after the instruction "move ra, at"(offset is 16)
     */
    ip = self_ra - (in_kernel_space(self_ra) ? 16 : 24);

    /*
     * search the text until finding the non-store instruction or "s{d,w}
     * ra, offset(sp)" instruction
     */
    do {
        /* get the code at "ip": code = *(unsigned int *)ip; */
        safe_load_code(code, ip, faulted);

        if (unlikely(faulted))
            return 0;
        /*
         * If we hit the non-store instruction before finding where the
         * ra is stored, then this is a leaf function and it does not
         * store the ra on the stack
         */
        if ((code & S_R_SP) != S_R_SP)
            return parent_ra_addr;

        /* Move to the next instruction */
        ip -= 4;
    } while ((code & S_RA_SP) != S_RA_SP);

    sp = fp + (code & OFFSET_MASK);

    /* tmp = *(unsigned long *)sp; */
    safe_load_stack(tmp, sp, faulted);
    if (unlikely(faulted))
        return 0;

    if (tmp == old_parent_ra)
        return sp;
    return 0;
}

#endif  /* !KBUILD_MCOUNT_RA_ADDRESS */

/*
 * Hook the return address and push it in the stack of return addrs
 * in current thread info.
 */
void prepare_ftrace_return(unsigned long *parent_ra_addr, unsigned long self_ra,
               unsigned long fp)
{
    unsigned long old_parent_ra;
    struct ftrace_graph_ent trace;
    unsigned long return_hooker = (unsigned long)
        &return_to_handler;
    int faulted, insns;

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

    /*
     * "parent_ra_addr" is the stack address saved the return address of
     * the caller of _mcount.
     *
     * if the gcc < 4.5, a leaf function does not save the return address
     * in the stack address, so, we "emulate" one in _mcount's stack space,
     * and hijack it directly, but for a non-leaf function, it save the
     * return address to the its own stack space, we can not hijack it
     * directly, but need to find the real stack address,
     * ftrace_get_parent_addr() does it!
     *
     * if gcc>= 4.5, with the new -mmcount-ra-address option, for a
     * non-leaf function, the location of the return address will be saved
     * to $12 for us, and for a leaf function, only put a zero into $12. we
     * do it in ftrace_graph_caller of mcount.S.
     */

    /* old_parent_ra = *parent_ra_addr; */
    safe_load_stack(old_parent_ra, parent_ra_addr, faulted);
    if (unlikely(faulted))
        goto out;
#ifndef KBUILD_MCOUNT_RA_ADDRESS
    parent_ra_addr = (unsigned long *)ftrace_get_parent_ra_addr(self_ra,
            old_parent_ra, (unsigned long)parent_ra_addr, fp);
    /*
     * If fails when getting the stack address of the non-leaf function's
     * ra, stop function graph tracer and return
     */
    if (parent_ra_addr == 0)
        goto out;
#endif
    /* *parent_ra_addr = return_hooker; */
    safe_store_stack(return_hooker, parent_ra_addr, faulted);
    if (unlikely(faulted))
        goto out;

    if (ftrace_push_return_trace(old_parent_ra, self_ra, &trace.depth, fp)
        == -EBUSY) {
        *parent_ra_addr = old_parent_ra;
        return;
    }

    /*
     * Get the recorded ip of the current mcount calling site in the
     * __mcount_loc section, which will be used to filter the function
     * entries configured through the tracing/set_graph_function interface.
     */

    insns = in_kernel_space(self_ra) ? 2 : MCOUNT_OFFSET_INSNS + 1;
    trace.func = self_ra - (MCOUNT_INSN_SIZE * insns);

    /* Only trace if the calling function expects to */
    if (!ftrace_graph_entry(&trace)) {
        current->curr_ret_stack--;
        *parent_ra_addr = old_parent_ra;
    }
    return;
out:
    ftrace_graph_stop();
    WARN_ON(1);
}
#endif  /* CONFIG_FUNCTION_GRAPH_TRACER */