ftrace.c

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/*
 * Dynamic function tracer architecture backend.
 *
 * Copyright IBM Corp. 2009
 *
 *   Author(s): Heiko Carstens <[email protected]>,
 *      Martin Schwidefsky <[email protected]>
 */

#include <linux/hardirq.h>
#include <linux/uaccess.h>
#include <linux/ftrace.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/kprobes.h>
#include <trace/syscall.h>
#include <asm/asm-offsets.h>

#ifdef CONFIG_64BIT
#define MCOUNT_OFFSET_RET 12
#else
#define MCOUNT_OFFSET_RET 22
#endif

#ifdef CONFIG_DYNAMIC_FTRACE

void ftrace_disable_code(void);
void ftrace_enable_insn(void);

#ifdef CONFIG_64BIT
/*
 * The 64-bit mcount code looks like this:
 *  stg %r14,8(%r15)        # offset 0
 * >    larl    %r1,<&counter>      # offset 6
 * >    brasl   %r14,_mcount        # offset 12
 *  lg  %r14,8(%r15)        # offset 18
 * Total length is 24 bytes. The middle two instructions of the mcount
 * block get overwritten by ftrace_make_nop / ftrace_make_call.
 * The 64-bit enabled ftrace code block looks like this:
 *  stg %r14,8(%r15)        # offset 0
 * >    lg  %r1,__LC_FTRACE_FUNC    # offset 6
 * >    lgr %r0,%r0         # offset 12
 * >    basr    %r14,%r1        # offset 16
 *  lg  %r14,8(%15)     # offset 18
 * The return points of the mcount/ftrace function have the same offset 18.
 * The 64-bit disable ftrace code block looks like this:
 *  stg %r14,8(%r15)        # offset 0
 * >    jg  .+18            # offset 6
 * >    lgr %r0,%r0         # offset 12
 * >    basr    %r14,%r1        # offset 16
 *  lg  %r14,8(%15)     # offset 18
 * The jg instruction branches to offset 24 to skip as many instructions
 * as possible.
 */
asm(
    "   .align  4\n"
    "ftrace_disable_code:\n"
    "   jg  0f\n"
    "   lgr %r0,%r0\n"
    "   basr    %r14,%r1\n"
    "0:\n"
    "   .align  4\n"
    "ftrace_enable_insn:\n"
    "   lg  %r1,"__stringify(__LC_FTRACE_FUNC)"\n");

#define FTRACE_INSN_SIZE    6

#else /* CONFIG_64BIT */
/*
 * The 31-bit mcount code looks like this:
 *  st  %r14,4(%r15)        # offset 0
 * >    bras    %r1,0f          # offset 4
 * >    .long   _mcount         # offset 8
 * >    .long   <&counter>      # offset 12
 * > 0: l   %r14,0(%r1)     # offset 16
 * >    l   %r1,4(%r1)      # offset 20
 *  basr    %r14,%r14       # offset 24
 *  l   %r14,4(%r15)        # offset 26
 * Total length is 30 bytes. The twenty bytes starting from offset 4
 * to offset 24 get overwritten by ftrace_make_nop / ftrace_make_call.
 * The 31-bit enabled ftrace code block looks like this:
 *  st  %r14,4(%r15)        # offset 0
 * >    l   %r14,__LC_FTRACE_FUNC   # offset 4
 * >    j   0f          # offset 8
 * >    .fill   12,1,0x07       # offset 12
 *   0: basr    %r14,%r14       # offset 24
 *  l   %r14,4(%r14)        # offset 26
 * The return points of the mcount/ftrace function have the same offset 26.
 * The 31-bit disabled ftrace code block looks like this:
 *  st  %r14,4(%r15)        # offset 0
 * >    j   .+26            # offset 4
 * >    j   0f          # offset 8
 * >    .fill   12,1,0x07       # offset 12
 *   0: basr    %r14,%r14       # offset 24
 *  l   %r14,4(%r14)        # offset 26
 * The j instruction branches to offset 30 to skip as many instructions
 * as possible.
 */
asm(
    "   .align  4\n"
    "ftrace_disable_code:\n"
    "   j   1f\n"
    "   j   0f\n"
    "   .fill   12,1,0x07\n"
    "0: basr    %r14,%r14\n"
    "1:\n"
    "   .align  4\n"
    "ftrace_enable_insn:\n"
    "   l   %r14,"__stringify(__LC_FTRACE_FUNC)"\n");

#define FTRACE_INSN_SIZE    4

#endif /* CONFIG_64BIT */


int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
            unsigned long addr)
{
    if (probe_kernel_write((void *) rec->ip, ftrace_disable_code,
                   MCOUNT_INSN_SIZE))
        return -EPERM;
    return 0;
}

int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
    if (probe_kernel_write((void *) rec->ip, ftrace_enable_insn,
                   FTRACE_INSN_SIZE))
        return -EPERM;
    return 0;
}

int ftrace_update_ftrace_func(ftrace_func_t func)
{
    return 0;
}

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

#endif /* CONFIG_DYNAMIC_FTRACE */

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
/*
 * Hook the return address and push it in the stack of return addresses
 * in current thread info.
 */
unsigned long __kprobes prepare_ftrace_return(unsigned long parent,
                          unsigned long ip)
{
    struct ftrace_graph_ent trace;

    if (unlikely(atomic_read(&current->tracing_graph_pause)))
        goto out;
    if (ftrace_push_return_trace(parent, ip, &trace.depth, 0) == -EBUSY)
        goto out;
    trace.func = (ip & PSW_ADDR_INSN) - MCOUNT_OFFSET_RET;
    /* Only trace if the calling function expects to. */
    if (!ftrace_graph_entry(&trace)) {
        current->curr_ret_stack--;
        goto out;
    }
    parent = (unsigned long) return_to_handler;
out:
    return parent;
}

#ifdef CONFIG_DYNAMIC_FTRACE
/*
 * Patch the kernel code at ftrace_graph_caller location. The instruction
 * there is branch relative and save to prepare_ftrace_return. To disable
 * the call to prepare_ftrace_return we patch the bras offset to point
 * directly after the instructions. To enable the call we calculate
 * the original offset to prepare_ftrace_return and put it back.
 */
int ftrace_enable_ftrace_graph_caller(void)
{
    unsigned short offset;

    offset = ((void *) prepare_ftrace_return -
          (void *) ftrace_graph_caller) / 2;
    return probe_kernel_write(ftrace_graph_caller + 2,
                  &offset, sizeof(offset));
}

int ftrace_disable_ftrace_graph_caller(void)
{
    static unsigned short offset = 0x0002;

    return probe_kernel_write(ftrace_graph_caller + 2,
                  &offset, sizeof(offset));
}

#endif /* CONFIG_DYNAMIC_FTRACE */
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */