ftrace.c

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/*
 * Code for replacing ftrace calls with jumps.
 *
 * Copyright (C) 2007-2008 Steven Rostedt <[email protected]>
 *
 * Thanks goes out to P.A. Semi, Inc for supplying me with a PPC64 box.
 *
 * Added function graph tracer code, taken from x86 that was written
 * by Frederic Weisbecker, and ported to PPC by Steven Rostedt.
 *
 */

#include <linux/spinlock.h>
#include <linux/hardirq.h>
#include <linux/uaccess.h>
#include <linux/module.h>
#include <linux/ftrace.h>
#include <linux/percpu.h>
#include <linux/init.h>
#include <linux/list.h>

#include <asm/cacheflush.h>
#include <asm/code-patching.h>
#include <asm/ftrace.h>
#include <asm/syscall.h>


#ifdef CONFIG_DYNAMIC_FTRACE
static unsigned int
ftrace_call_replace(unsigned long ip, unsigned long addr, int link)
{
    unsigned int op;

    addr = ppc_function_entry((void *)addr);

    /* if (link) set op to 'bl' else 'b' */
    op = create_branch((unsigned int *)ip, addr, link ? 1 : 0);

    return op;
}

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

    /*
     * 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.
     */

    /* 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 (replaced != old)
        return -EINVAL;

    /* replace the text with the new text */
    if (patch_instruction((unsigned int *)ip, new))
        return -EPERM;

    return 0;
}

/*
 * Helper functions that are the same for both PPC64 and PPC32.
 */
static int test_24bit_addr(unsigned long ip, unsigned long addr)
{

    /* use the create_branch to verify that this offset can be branched */
    return create_branch((unsigned int *)ip, addr, 0);
}

#ifdef CONFIG_MODULES

static int is_bl_op(unsigned int op)
{
    return (op & 0xfc000003) == 0x48000001;
}

static unsigned long find_bl_target(unsigned long ip, unsigned int op)
{
    static int offset;

    offset = (op & 0x03fffffc);
    /* make it signed */
    if (offset & 0x02000000)
        offset |= 0xfe000000;

    return ip + (long)offset;
}

#ifdef CONFIG_PPC64
static int
__ftrace_make_nop(struct module *mod,
          struct dyn_ftrace *rec, unsigned long addr)
{
    unsigned int op;
    unsigned int jmp[5];
    unsigned long ptr;
    unsigned long ip = rec->ip;
    unsigned long tramp;
    int offset;

    /* read where this goes */
    if (probe_kernel_read(&op, (void *)ip, sizeof(int)))
        return -EFAULT;

    /* Make sure that that this is still a 24bit jump */
    if (!is_bl_op(op)) {
        printk(KERN_ERR "Not expected bl: opcode is %x\n", op);
        return -EINVAL;
    }

    /* lets find where the pointer goes */
    tramp = find_bl_target(ip, op);

    /*
     * On PPC64 the trampoline looks like:
     * 0x3d, 0x82, 0x00, 0x00,    addis   r12,r2, <high>
     * 0x39, 0x8c, 0x00, 0x00,    addi    r12,r12, <low>
     *   Where the bytes 2,3,6 and 7 make up the 32bit offset
     *   to the TOC that holds the pointer.
     *   to jump to.
     * 0xf8, 0x41, 0x00, 0x28,    std     r2,40(r1)
     * 0xe9, 0x6c, 0x00, 0x20,    ld      r11,32(r12)
     *   The actually address is 32 bytes from the offset
     *   into the TOC.
     * 0xe8, 0x4c, 0x00, 0x28,    ld      r2,40(r12)
     */

    pr_devel("ip:%lx jumps to %lx r2: %lx", ip, tramp, mod->arch.toc);

    /* Find where the trampoline jumps to */
    if (probe_kernel_read(jmp, (void *)tramp, sizeof(jmp))) {
        printk(KERN_ERR "Failed to read %lx\n", tramp);
        return -EFAULT;
    }

    pr_devel(" %08x %08x", jmp[0], jmp[1]);

    /* verify that this is what we expect it to be */
    if (((jmp[0] & 0xffff0000) != 0x3d820000) ||
        ((jmp[1] & 0xffff0000) != 0x398c0000) ||
        (jmp[2] != 0xf8410028) ||
        (jmp[3] != 0xe96c0020) ||
        (jmp[4] != 0xe84c0028)) {
        printk(KERN_ERR "Not a trampoline\n");
        return -EINVAL;
    }

    /* The bottom half is signed extended */
    offset = ((unsigned)((unsigned short)jmp[0]) << 16) +
        (int)((short)jmp[1]);

    pr_devel(" %x ", offset);

    /* get the address this jumps too */
    tramp = mod->arch.toc + offset + 32;
    pr_devel("toc: %lx", tramp);

    if (probe_kernel_read(jmp, (void *)tramp, 8)) {
        printk(KERN_ERR "Failed to read %lx\n", tramp);
        return -EFAULT;
    }

    pr_devel(" %08x %08x\n", jmp[0], jmp[1]);

    ptr = ((unsigned long)jmp[0] << 32) + jmp[1];

    /* This should match what was called */
    if (ptr != ppc_function_entry((void *)addr)) {
        printk(KERN_ERR "addr does not match %lx\n", ptr);
        return -EINVAL;
    }

    /*
     * We want to nop the line, but the next line is
     *  0xe8, 0x41, 0x00, 0x28   ld r2,40(r1)
     * This needs to be turned to a nop too.
     */
    if (probe_kernel_read(&op, (void *)(ip+4), MCOUNT_INSN_SIZE))
        return -EFAULT;

    if (op != 0xe8410028) {
        printk(KERN_ERR "Next line is not ld! (%08x)\n", op);
        return -EINVAL;
    }

    /*
     * Milton Miller pointed out that we can not blindly do nops.
     * If a task was preempted when calling a trace function,
     * the nops will remove the way to restore the TOC in r2
     * and the r2 TOC will get corrupted.
     */

    /*
     * Replace:
     *   bl <tramp>  <==== will be replaced with "b 1f"
     *   ld r2,40(r1)
     *  1:
     */
    op = 0x48000008;    /* b +8 */

    if (patch_instruction((unsigned int *)ip, op))
        return -EPERM;

    return 0;
}

#else /* !PPC64 */
static int
__ftrace_make_nop(struct module *mod,
          struct dyn_ftrace *rec, unsigned long addr)
{
    unsigned int op;
    unsigned int jmp[4];
    unsigned long ip = rec->ip;
    unsigned long tramp;

    if (probe_kernel_read(&op, (void *)ip, MCOUNT_INSN_SIZE))
        return -EFAULT;

    /* Make sure that that this is still a 24bit jump */
    if (!is_bl_op(op)) {
        printk(KERN_ERR "Not expected bl: opcode is %x\n", op);
        return -EINVAL;
    }

    /* lets find where the pointer goes */
    tramp = find_bl_target(ip, op);

    /*
     * On PPC32 the trampoline looks like:
     *  0x3d, 0x80, 0x00, 0x00  lis r12,sym@ha
     *  0x39, 0x8c, 0x00, 0x00  addi r12,r12,sym@l
     *  0x7d, 0x89, 0x03, 0xa6  mtctr r12
     *  0x4e, 0x80, 0x04, 0x20  bctr
     */

    pr_devel("ip:%lx jumps to %lx", ip, tramp);

    /* Find where the trampoline jumps to */
    if (probe_kernel_read(jmp, (void *)tramp, sizeof(jmp))) {
        printk(KERN_ERR "Failed to read %lx\n", tramp);
        return -EFAULT;
    }

    pr_devel(" %08x %08x ", jmp[0], jmp[1]);

    /* verify that this is what we expect it to be */
    if (((jmp[0] & 0xffff0000) != 0x3d800000) ||
        ((jmp[1] & 0xffff0000) != 0x398c0000) ||
        (jmp[2] != 0x7d8903a6) ||
        (jmp[3] != 0x4e800420)) {
        printk(KERN_ERR "Not a trampoline\n");
        return -EINVAL;
    }

    tramp = (jmp[1] & 0xffff) |
        ((jmp[0] & 0xffff) << 16);
    if (tramp & 0x8000)
        tramp -= 0x10000;

    pr_devel(" %lx ", tramp);

    if (tramp != addr) {
        printk(KERN_ERR
               "Trampoline location %08lx does not match addr\n",
               tramp);
        return -EINVAL;
    }

    op = PPC_INST_NOP;

    if (patch_instruction((unsigned int *)ip, op))
        return -EPERM;

    return 0;
}
#endif /* PPC64 */
#endif /* CONFIG_MODULES */

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

    /*
     * If the calling address is more that 24 bits away,
     * then we had to use a trampoline to make the call.
     * Otherwise just update the call site.
     */
    if (test_24bit_addr(ip, addr)) {
        /* within range */
        old = ftrace_call_replace(ip, addr, 1);
        new = PPC_INST_NOP;
        return ftrace_modify_code(ip, old, new);
    }

#ifdef CONFIG_MODULES
    /*
     * Out of range jumps are called from modules.
     * We should either already have a pointer to the module
     * or it has been passed in.
     */
    if (!rec->arch.mod) {
        if (!mod) {
            printk(KERN_ERR "No module loaded addr=%lx\n",
                   addr);
            return -EFAULT;
        }
        rec->arch.mod = mod;
    } else if (mod) {
        if (mod != rec->arch.mod) {
            printk(KERN_ERR
                   "Record mod %p not equal to passed in mod %p\n",
                   rec->arch.mod, mod);
            return -EINVAL;
        }
        /* nothing to do if mod == rec->arch.mod */
    } else
        mod = rec->arch.mod;

    return __ftrace_make_nop(mod, rec, addr);
#else
    /* We should not get here without modules */
    return -EINVAL;
#endif /* CONFIG_MODULES */
}

#ifdef CONFIG_MODULES
#ifdef CONFIG_PPC64
static int
__ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
    unsigned int op[2];
    unsigned long ip = rec->ip;

    /* read where this goes */
    if (probe_kernel_read(op, (void *)ip, MCOUNT_INSN_SIZE * 2))
        return -EFAULT;

    /*
     * It should be pointing to two nops or
     *  b +8; ld r2,40(r1)
     */
    if (((op[0] != 0x48000008) || (op[1] != 0xe8410028)) &&
        ((op[0] != PPC_INST_NOP) || (op[1] != PPC_INST_NOP))) {
        printk(KERN_ERR "Expected NOPs but have %x %x\n", op[0], op[1]);
        return -EINVAL;
    }

    /* If we never set up a trampoline to ftrace_caller, then bail */
    if (!rec->arch.mod->arch.tramp) {
        printk(KERN_ERR "No ftrace trampoline\n");
        return -EINVAL;
    }

    /* create the branch to the trampoline */
    op[0] = create_branch((unsigned int *)ip,
                  rec->arch.mod->arch.tramp, BRANCH_SET_LINK);
    if (!op[0]) {
        printk(KERN_ERR "REL24 out of range!\n");
        return -EINVAL;
    }

    /* ld r2,40(r1) */
    op[1] = 0xe8410028;

    pr_devel("write to %lx\n", rec->ip);

    if (probe_kernel_write((void *)ip, op, MCOUNT_INSN_SIZE * 2))
        return -EPERM;

    flush_icache_range(ip, ip + 8);

    return 0;
}
#else
static int
__ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
    unsigned int op;
    unsigned long ip = rec->ip;

    /* read where this goes */
    if (probe_kernel_read(&op, (void *)ip, MCOUNT_INSN_SIZE))
        return -EFAULT;

    /* It should be pointing to a nop */
    if (op != PPC_INST_NOP) {
        printk(KERN_ERR "Expected NOP but have %x\n", op);
        return -EINVAL;
    }

    /* If we never set up a trampoline to ftrace_caller, then bail */
    if (!rec->arch.mod->arch.tramp) {
        printk(KERN_ERR "No ftrace trampoline\n");
        return -EINVAL;
    }

    /* create the branch to the trampoline */
    op = create_branch((unsigned int *)ip,
               rec->arch.mod->arch.tramp, BRANCH_SET_LINK);
    if (!op) {
        printk(KERN_ERR "REL24 out of range!\n");
        return -EINVAL;
    }

    pr_devel("write to %lx\n", rec->ip);

    if (patch_instruction((unsigned int *)ip, op))
        return -EPERM;

    return 0;
}
#endif /* CONFIG_PPC64 */
#endif /* CONFIG_MODULES */

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

    /*
     * If the calling address is more that 24 bits away,
     * then we had to use a trampoline to make the call.
     * Otherwise just update the call site.
     */
    if (test_24bit_addr(ip, addr)) {
        /* within range */
        old = PPC_INST_NOP;
        new = ftrace_call_replace(ip, addr, 1);
        return ftrace_modify_code(ip, old, new);
    }

#ifdef CONFIG_MODULES
    /*
     * Out of range jumps are called from modules.
     * Being that we are converting from nop, it had better
     * already have a module defined.
     */
    if (!rec->arch.mod) {
        printk(KERN_ERR "No module loaded\n");
        return -EINVAL;
    }

    return __ftrace_make_call(rec, addr);
#else
    /* We should not get here without modules */
    return -EINVAL;
#endif /* CONFIG_MODULES */
}

int ftrace_update_ftrace_func(ftrace_func_t func)
{
    unsigned long ip = (unsigned long)(&ftrace_call);
    unsigned int old, new;
    int ret;

    old = *(unsigned int *)&ftrace_call;
    new = ftrace_call_replace(ip, (unsigned long)func, 1);
    ret = ftrace_modify_code(ip, old, new);

    return ret;
}

static int __ftrace_replace_code(struct dyn_ftrace *rec, int enable)
{
    unsigned long ftrace_addr = (unsigned long)FTRACE_ADDR;
    int ret;

    ret = ftrace_update_record(rec, enable);

    switch (ret) {
    case FTRACE_UPDATE_IGNORE:
        return 0;
    case FTRACE_UPDATE_MAKE_CALL:
        return ftrace_make_call(rec, ftrace_addr);
    case FTRACE_UPDATE_MAKE_NOP:
        return ftrace_make_nop(NULL, rec, ftrace_addr);
    }

    return 0;
}

void ftrace_replace_code(int enable)
{
    struct ftrace_rec_iter *iter;
    struct dyn_ftrace *rec;
    int ret;

    for (iter = ftrace_rec_iter_start(); iter;
         iter = ftrace_rec_iter_next(iter)) {
        rec = ftrace_rec_iter_record(iter);
        ret = __ftrace_replace_code(rec, enable);
        if (ret) {
            ftrace_bug(ret, rec->ip);
            return;
        }
    }
}

void arch_ftrace_update_code(int command)
{
    if (command & FTRACE_UPDATE_CALLS)
        ftrace_replace_code(1);
    else if (command & FTRACE_DISABLE_CALLS)
        ftrace_replace_code(0);

    if (command & FTRACE_UPDATE_TRACE_FUNC)
        ftrace_update_ftrace_func(ftrace_trace_function);

    if (command & FTRACE_START_FUNC_RET)
        ftrace_enable_ftrace_graph_caller();
    else if (command & FTRACE_STOP_FUNC_RET)
        ftrace_disable_ftrace_graph_caller();
}

int __init ftrace_dyn_arch_init(void *data)
{
    /* caller expects data to be zero */
    unsigned long *p = data;

    *p = 0;

    return 0;
}
#endif /* CONFIG_DYNAMIC_FTRACE */

#ifdef CONFIG_FUNCTION_GRAPH_TRACER

#ifdef CONFIG_DYNAMIC_FTRACE
extern void ftrace_graph_call(void);
extern void ftrace_graph_stub(void);

int ftrace_enable_ftrace_graph_caller(void)
{
    unsigned long ip = (unsigned long)(&ftrace_graph_call);
    unsigned long addr = (unsigned long)(&ftrace_graph_caller);
    unsigned long stub = (unsigned long)(&ftrace_graph_stub);
    unsigned int old, new;

    old = ftrace_call_replace(ip, stub, 0);
    new = ftrace_call_replace(ip, addr, 0);

    return ftrace_modify_code(ip, old, new);
}

int ftrace_disable_ftrace_graph_caller(void)
{
    unsigned long ip = (unsigned long)(&ftrace_graph_call);
    unsigned long addr = (unsigned long)(&ftrace_graph_caller);
    unsigned long stub = (unsigned long)(&ftrace_graph_stub);
    unsigned int old, new;

    old = ftrace_call_replace(ip, addr, 0);
    new = ftrace_call_replace(ip, stub, 0);

    return ftrace_modify_code(ip, old, new);
}
#endif /* CONFIG_DYNAMIC_FTRACE */

#ifdef CONFIG_PPC64
extern void mod_return_to_handler(void);
#endif

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

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

#ifdef CONFIG_PPC64
    /* non core kernel code needs to save and restore the TOC */
    if (REGION_ID(self_addr) != KERNEL_REGION_ID)
        return_hooker = (unsigned long)&mod_return_to_handler;
#endif

    return_hooker = ppc_function_entry((void *)return_hooker);

    /*
     * Protect against fault, even if it shouldn't
     * happen. This tool is too much intrusive to
     * ignore such a protection.
     */
    asm volatile(
        "1: " PPC_LL "%[old], 0(%[parent])\n"
        "2: " PPC_STL "%[return_hooker], 0(%[parent])\n"
        "   li %[faulted], 0\n"
        "3:\n"

        ".section .fixup, \"ax\"\n"
        "4: li %[faulted], 1\n"
        "   b 3b\n"
        ".previous\n"

        ".section __ex_table,\"a\"\n"
            PPC_LONG_ALIGN "\n"
            PPC_LONG "1b,4b\n"
            PPC_LONG "2b,4b\n"
        ".previous"

        : [old] "=&r" (old), [faulted] "=r" (faulted)
        : [parent] "r" (parent), [return_hooker] "r" (return_hooker)
        : "memory"
    );

    if (unlikely(faulted)) {
        ftrace_graph_stop();
        WARN_ON(1);
        return;
    }

    trace.func = self_addr;
    trace.depth = current->curr_ret_stack + 1;

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

    if (ftrace_push_return_trace(old, self_addr, &trace.depth, 0) == -EBUSY)
        *parent = old;
}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */

#if defined(CONFIG_FTRACE_SYSCALLS) && defined(CONFIG_PPC64)
unsigned long __init arch_syscall_addr(int nr)
{
    return sys_call_table[nr*2];
}
#endif /* CONFIG_FTRACE_SYSCALLS && CONFIG_PPC64 */