From 538f19526e40ce7a5a296fad6a3121409c890adc Mon Sep 17 00:00:00 2001 From: Wu Zhangjin Date: Fri, 20 Nov 2009 20:34:32 +0800 Subject: 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 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 Cc: Nicholas Mc Guire Cc: zhangfx@lemote.com Cc: Wu Zhangjin Cc: Ingo Molnar Cc: Thomas Gleixner Cc: Frederic Weisbecker Cc: linux-kernel@vger.kernel.org Cc: linux-mips@linux-mips.org Patchwork: http://patchwork.linux-mips.org/patch/675/ Acked-by: Steven Rostedt Signed-off-by: Ralf Baechle --- arch/mips/kernel/ftrace.c | 112 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 112 insertions(+) create mode 100644 arch/mips/kernel/ftrace.c (limited to 'arch/mips/kernel/ftrace.c') diff --git a/arch/mips/kernel/ftrace.c b/arch/mips/kernel/ftrace.c new file mode 100644 index 00000000000..5459a783837 --- /dev/null +++ b/arch/mips/kernel/ftrace.c @@ -0,0 +1,112 @@ +/* + * Code for replacing ftrace calls with jumps. + * + * Copyright (C) 2007-2008 Steven Rostedt + * Copyright (C) 2009 DSLab, Lanzhou University, China + * Author: Wu Zhangjin + * + * Thanks goes to Steven Rostedt for writing the original x86 version. + */ + +#include +#include +#include + +#include + +#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 */ -- cgit v1.2.3-18-g5258