linux/arch/s390/kernel/ftrace.c
Heiko Carstens 05e0baaf9b s390/ftrace: prepare_ftrace_return() function call order
Steven Rostedt noted that s390 is the only architecture which calls
ftrace_push_return_trace() before ftrace_graph_entry() and therefore has
the small advantage that trace.depth gets initialized automatically.

However this small advantage isn't worth the difference and possible subtle
breakage that may result from this.
So change s390 to have the same function call order like all other
architectures: first ftrace_graph_entry(), then ftrace_push_return_trace()

Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2013-10-24 17:17:03 +02:00

194 lines
5.2 KiB
C

/*
* 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>
#include "entry.h"
#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;
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;
}
#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((void *) ftrace_graph_caller + 2,
&offset, sizeof(offset));
}
int ftrace_disable_ftrace_graph_caller(void)
{
static unsigned short offset = 0x0002;
return probe_kernel_write((void *) ftrace_graph_caller + 2,
&offset, sizeof(offset));
}
#endif /* CONFIG_DYNAMIC_FTRACE */
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */