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linux-next/arch/mips/kernel/ftrace.c

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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: Wu 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: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2009-11-20 20:34:32 +08:00
/*
* 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 */
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