/*
* Dynamic function tracer architecture backend.
*
* Copyright IBM Corp. 2009
*
* 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>
#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(¤t->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 */
