Commit 538f1952 authored by Wu Zhangjin's avatar Wu Zhangjin Committed by Ralf Baechle

MIPS: Tracing: Add dynamic function tracer support

With dynamic function tracer, by default, _mcount is defined as an
"empty" function, it returns directly without any more action . When
enabling it in user-space, it will jump to a real tracing
function(ftrace_caller), and do the real job for us.

Differ from the static function tracer, dynamic function tracer provides
two functions ftrace_make_call()/ftrace_make_nop() to enable/disable the
tracing of some indicated kernel functions(set_ftrace_filter).

In the -v4 version, the implementation of this support is basically the same as
X86 version does: _mcount is implemented as an empty function and ftrace_caller
is implemented as a real tracing function respectively.

But in this version, to support module tracing with the help of
-mlong-calls in arch/mips/Makefile:

MODFLAGS += -mlong-calls.

The stuff becomes a little more complex. We need to cope with two
different type of calling to _mcount.

For the kernel part, the calling to _mcount(result of "objdump -hdr
vmlinux"). is like this:

	108:   03e0082d        move    at,ra
	10c:   0c000000        jal     0 <fpcsr_pending>
                        10c: R_MIPS_26  _mcount
                        10c: R_MIPS_NONE        *ABS*
                        10c: R_MIPS_NONE        *ABS*
	110:   00020021        nop

For the module with -mlong-calls, it looks like this:

	c:	3c030000 	lui	v1,0x0
			c: R_MIPS_HI16	_mcount
			c: R_MIPS_NONE	*ABS*
			c: R_MIPS_NONE	*ABS*
	10:	64630000 	daddiu	v1,v1,0
			10: R_MIPS_LO16	_mcount
			10: R_MIPS_NONE	*ABS*
			10: R_MIPS_NONE	*ABS*
	14:	03e0082d 	move	at,ra
	18:	0060f809 	jalr	v1

In the kernel version, there is only one "_mcount" string for every
kernel function, so, we just need to match this one in mcount_regex of
scripts/recordmcount.pl, but in the module version, we need to choose
one of the two to match. Herein, I choose the first one with
"R_MIPS_HI16 _mcount".

and In the kernel verion, without module tracing support, we just need
to replace "jal _mcount" by "jal ftrace_caller" to do real tracing, and
filter the tracing of some kernel functions via replacing it by a nop
instruction.

but as we have described before, the instruction "jal ftrace_caller" only left
32bit length for the address of ftrace_caller, it will fail when calling from
the module space. so, herein, we must replace something else.

the basic idea is loading the address of ftrace_caller to v1 via changing these
two instructions:

	lui	v1,0x0
	addiu	v1,v1,0

If we want to enable the tracing, we need to replace the above instructions to:

	lui	v1, HI_16BIT_ftrace_caller
	addiu	v1, v1, LOW_16BIT_ftrace_caller

If we want to stop the tracing of the indicated kernel functions, we
just need to replace the "jalr v1" to a nop instruction. but we need to
replace two instructions and encode the above two instructions
oursevles.

Is there a simpler solution? Yes! Here it is, in this version, we put _mcount
and ftrace_caller together, which means the address of _mcount and
ftrace_caller is the same:

_mcount:
ftrace_caller:
	j	ftrace_stub
	 nop

	...(do real tracing here)...

ftrace_stub:
	jr	ra
	 move	ra, at

By default, the kernel functions call _mcount, and then jump to ftrace_stub and
return. and when we want to do real tracing, we just need to remove that "j
ftrace_stub", and it will run through the two "nop" instructions and then do
the real tracing job.

what about filtering job? we just need to do this:

	 lui v1, hi_16bit_of_mcount        <--> b 1f (0x10000004)
	 addiu v1, v1, low_16bit_of_mcount
	 move at, ra
	 jalr v1
	 nop
	 				     1f: (rec->ip + 12)

In linux-mips64, there will be some local symbols, whose name are
prefixed by $L, which need to be filtered. thanks goes to Steven for
writing the mips64-specific function_regex.

In a conclusion, with RISC, things becomes easier with such a "stupid"
trick, RISC is something like K.I.S.S, and also, there are lots of
"simple" tricks in the whole ftrace support, thanks goes to Steven and
the other folks for providing such a wonderful tracing framework!
Signed-off-by: default avatarWu Zhangjin <wuzhangjin@gmail.com>
Cc: Nicholas Mc Guire <der.herr@hofr.at>
Cc: zhangfx@lemote.com
Cc: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/675/Acked-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent e6299d26
......@@ -7,6 +7,8 @@ config MIPS
select HAVE_ARCH_KGDB
select HAVE_FUNCTION_TRACER
select HAVE_FUNCTION_TRACE_MCOUNT_TEST
select HAVE_DYNAMIC_FTRACE
select HAVE_FTRACE_MCOUNT_RECORD
# Horrible source of confusion. Die, die, die ...
select EMBEDDED
select RTC_LIB if !MACH_LOONGSON
......
......@@ -19,6 +19,15 @@
extern void _mcount(void);
#define mcount _mcount
#ifdef CONFIG_DYNAMIC_FTRACE
static inline unsigned long ftrace_call_adjust(unsigned long addr)
{
return addr;
}
struct dyn_arch_ftrace {
};
#endif /* CONFIG_DYNAMIC_FTRACE */
#endif /* __ASSEMBLY__ */
#endif /* CONFIG_FUNCTION_TRACER */
#endif /* _ASM_MIPS_FTRACE_H */
......@@ -11,6 +11,7 @@ obj-y += cpu-probe.o branch.o entry.o genex.o irq.o process.o \
time.o topology.o traps.o unaligned.o watch.o
ifdef CONFIG_FUNCTION_TRACER
CFLAGS_REMOVE_ftrace.o = -pg
CFLAGS_REMOVE_early_printk.o = -pg
endif
......@@ -31,7 +32,7 @@ obj-$(CONFIG_SYNC_R4K) += sync-r4k.o
obj-$(CONFIG_STACKTRACE) += stacktrace.o
obj-$(CONFIG_MODULES) += mips_ksyms.o module.o
obj-$(CONFIG_FUNCTION_TRACER) += mcount.o
obj-$(CONFIG_FUNCTION_TRACER) += mcount.o ftrace.o
obj-$(CONFIG_CPU_LOONGSON2) += r4k_fpu.o r4k_switch.o
obj-$(CONFIG_CPU_MIPS32) += r4k_fpu.o r4k_switch.o
......
/*
* Code for replacing ftrace calls with jumps.
*
* Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
* Copyright (C) 2009 DSLab, Lanzhou University, China
* Author: Wu Zhangjin <wuzj@lemote.com>
*
* Thanks goes to Steven Rostedt for writing the original x86 version.
*/
#include <linux/uaccess.h>
#include <linux/init.h>
#include <linux/ftrace.h>
#include <asm/cacheflush.h>
#ifdef CONFIG_DYNAMIC_FTRACE
#define JAL 0x0c000000 /* jump & link: ip --> ra, jump to target */
#define ADDR_MASK 0x03ffffff /* op_code|addr : 31...26|25 ....0 */
#define jump_insn_encode(op_code, addr) \
((unsigned int)((op_code) | (((addr) >> 2) & ADDR_MASK)))
static unsigned int ftrace_nop = 0x00000000;
static int ftrace_modify_code(unsigned long ip, unsigned int new_code)
{
*(unsigned int *)ip = new_code;
flush_icache_range(ip, ip + 8);
return 0;
}
static int lui_v1;
static int jal_mcount;
int ftrace_make_nop(struct module *mod,
struct dyn_ftrace *rec, unsigned long addr)
{
unsigned int new;
unsigned long ip = rec->ip;
/* We have compiled module with -mlong-calls, but compiled the kernel
* without it, we need to cope with them respectively. */
if (ip & 0x40000000) {
/* record it for ftrace_make_call */
if (lui_v1 == 0)
lui_v1 = *(unsigned int *)ip;
/* lui v1, hi_16bit_of_mcount --> b 1f (0x10000004)
* addiu v1, v1, low_16bit_of_mcount
* move at, ra
* jalr v1
* nop
* 1f: (ip + 12)
*/
new = 0x10000004;
} else {
/* record/calculate it for ftrace_make_call */
if (jal_mcount == 0) {
/* We can record it directly like this:
* jal_mcount = *(unsigned int *)ip;
* Herein, jump over the first two nop instructions */
jal_mcount = jump_insn_encode(JAL, (MCOUNT_ADDR + 8));
}
/* move at, ra
* jalr v1 --> nop
*/
new = ftrace_nop;
}
return ftrace_modify_code(ip, new);
}
static int modified; /* initialized as 0 by default */
int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
unsigned int new;
unsigned long ip = rec->ip;
/* We just need to remove the "b ftrace_stub" at the fist time! */
if (modified == 0) {
modified = 1;
ftrace_modify_code(addr, ftrace_nop);
}
/* ip, module: 0xc0000000, kernel: 0x80000000 */
new = (ip & 0x40000000) ? lui_v1 : jal_mcount;
return ftrace_modify_code(ip, new);
}
#define FTRACE_CALL_IP ((unsigned long)(&ftrace_call))
int ftrace_update_ftrace_func(ftrace_func_t func)
{
unsigned int new;
new = jump_insn_encode(JAL, (unsigned long)func);
return ftrace_modify_code(FTRACE_CALL_IP, new);
}
int __init ftrace_dyn_arch_init(void *data)
{
/* The return code is retured via data */
*(unsigned long *)data = 0;
return 0;
}
#endif /* CONFIG_DYNAMIC_FTRACE */
......@@ -58,6 +58,33 @@
move ra, AT
.endm
#ifdef CONFIG_DYNAMIC_FTRACE
NESTED(ftrace_caller, PT_SIZE, ra)
.globl _mcount
_mcount:
b ftrace_stub
nop
lw t0, function_trace_stop
bnez t0, ftrace_stub
nop
MCOUNT_SAVE_REGS
move a0, ra /* arg1: next ip, selfaddr */
.globl ftrace_call
ftrace_call:
nop /* a placeholder for the call to a real tracing function */
move a1, AT /* arg2: the caller's next ip, parent */
MCOUNT_RESTORE_REGS
.globl ftrace_stub
ftrace_stub:
RETURN_BACK
END(ftrace_caller)
#else /* ! CONFIG_DYNAMIC_FTRACE */
NESTED(_mcount, PT_SIZE, ra)
lw t0, function_trace_stop
bnez t0, ftrace_stub
......@@ -82,5 +109,7 @@ ftrace_stub:
RETURN_BACK
END(_mcount)
#endif /* ! CONFIG_DYNAMIC_FTRACE */
.set at
.set reorder
......@@ -295,6 +295,58 @@ if ($arch eq "x86_64") {
$ld .= " -m elf64_sparc";
$cc .= " -m64";
$objcopy .= " -O elf64-sparc";
} elsif ($arch eq "mips") {
# To enable module support, we need to enable the -mlong-calls option
# of gcc for module, after using this option, we can not get the real
# offset of the calling to _mcount, but the offset of the lui
# instruction or the addiu one. herein, we record the address of the
# first one, and then we can replace this instruction by a branch
# instruction to jump over the profiling function to filter the
# indicated functions, or swith back to the lui instruction to trace
# them, which means dynamic tracing.
#
# c: 3c030000 lui v1,0x0
# c: R_MIPS_HI16 _mcount
# c: R_MIPS_NONE *ABS*
# c: R_MIPS_NONE *ABS*
# 10: 64630000 daddiu v1,v1,0
# 10: R_MIPS_LO16 _mcount
# 10: R_MIPS_NONE *ABS*
# 10: R_MIPS_NONE *ABS*
# 14: 03e0082d move at,ra
# 18: 0060f809 jalr v1
#
# for the kernel:
#
# 10: 03e0082d move at,ra
# 14: 0c000000 jal 0 <loongson_halt>
# 14: R_MIPS_26 _mcount
# 14: R_MIPS_NONE *ABS*
# 14: R_MIPS_NONE *ABS*
# 18: 00020021 nop
if ($is_module eq "0") {
$mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$";
} else {
$mcount_regex = "^\\s*([0-9a-fA-F]+): R_MIPS_HI16\\s+_mcount\$";
}
$objdump .= " -Melf-trad".$endian."mips ";
if ($endian eq "big") {
$endian = " -EB ";
$ld .= " -melf".$bits."btsmip";
} else {
$endian = " -EL ";
$ld .= " -melf".$bits."ltsmip";
}
$cc .= " -mno-abicalls -fno-pic -mabi=" . $bits . $endian;
$ld .= $endian;
if ($bits == 64) {
$function_regex =
"^([0-9a-fA-F]+)\\s+<(.|[^\$]L.*?|\$[^L].*?|[^\$][^L].*?)>:";
$type = ".dword";
}
} elsif ($arch eq "microblaze") {
# Microblaze calls '_mcount' instead of plain 'mcount'.
$mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$";
......
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