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/*
* Dynamic function tracer architecture backend.
*
* Copyright IBM Corp. 2009,2014
*
* Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
* Martin Schwidefsky <schwidefsky@de.ibm.com>
*/
#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>
#include "entry.h"
void mcount_replace_code(void);
void ftrace_disable_code(void);
void ftrace_enable_insn(void);
/*
* The 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 complete mcount block initially gets replaced
* by ftrace_make_nop. Subsequent calls to ftrace_make_call / ftrace_make_nop
* only patch the jg/lg instruction within the block.
* Note: we do not patch the first instruction to an unconditional branch,
* since that would break kprobes/jprobes. It is easier to leave the larl
* instruction in and only modify the second instruction.
* The enabled ftrace code block looks like this:
* larl %r0,.+24 # offset 0
* > lg %r1,__LC_FTRACE_FUNC # offset 6
* br %r1 # offset 12
* brcl 0,0 # offset 14
* brc 0,0 # offset 20
* The ftrace function gets called with a non-standard C function call ABI
* where r0 contains the return address. It is also expected that the called
* function only clobbers r0 and r1, but restores r2-r15.
* The return point of the ftrace function has offset 24, so execution
* continues behind the mcount block.
* larl %r0,.+24 # offset 0
* > jg .+18 # offset 6
* br %r1 # offset 12
* brcl 0,0 # offset 14
* brc 0,0 # offset 20
* The jg instruction branches to offset 24 to skip as many instructions
* as possible.
*/
asm(
" .align 4\n"
"mcount_replace_code:\n"
" larl %r0,0f\n"
"ftrace_disable_code:\n"
" jg 0f\n"
" br %r1\n"
" brcl 0,0\n"
" brc 0,0\n"
"0:\n"
" .align 4\n"
"ftrace_enable_insn:\n"
" lg %r1,"__stringify(__LC_FTRACE_FUNC)"\n");
#define MCOUNT_BLOCK_SIZE 24
#define MCOUNT_INSN_OFFSET 6
#define FTRACE_INSN_SIZE 6
int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
unsigned long addr)
{
return 0;
}
int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
unsigned long addr)
{
/* Initial replacement of the whole mcount block */
if (addr == MCOUNT_ADDR) {
if (probe_kernel_write((void *) rec->ip - MCOUNT_INSN_OFFSET,
mcount_replace_code,
MCOUNT_BLOCK_SIZE))
return -EPERM;
return 0;
}
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)
{
return 0;
}
#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(¤t->tracing_graph_pause)))
goto out;
ip = (ip & PSW_ADDR_INSN) - MCOUNT_INSN_SIZE;
trace.func = ip;
trace.depth = current->curr_ret_stack + 1;
/* Only trace if the calling function expects to. */
if (!ftrace_graph_entry(&trace))
goto out;
if (ftrace_push_return_trace(parent, ip, &trace.depth, 0) == -EBUSY)
goto out;
parent = (unsigned long) return_to_handler;
out:
return parent;
}
/*
* Patch the kernel code at ftrace_graph_caller location. The instruction
* there is branch relative on condition. To enable the ftrace graph code
* block, we simply patch the mask field of the instruction to zero and
* turn the instruction into a nop.
* To disable the ftrace graph code the mask field will be patched to
* all ones, which turns the instruction into an unconditional branch.
*/
int ftrace_enable_ftrace_graph_caller(void)
{
u8 op = 0x04; /* set mask field to zero */
return probe_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
}
int ftrace_disable_ftrace_graph_caller(void)
{
u8 op = 0xf4; /* set mask field to all ones */
return probe_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
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