forked from Minki/linux
538f19526e
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>
113 lines
2.7 KiB
C
113 lines
2.7 KiB
C
/*
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* Code for replacing ftrace calls with jumps.
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*
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* Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
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* Copyright (C) 2009 DSLab, Lanzhou University, China
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* Author: Wu Zhangjin <wuzj@lemote.com>
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*
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* Thanks goes to Steven Rostedt for writing the original x86 version.
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*/
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#include <linux/uaccess.h>
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#include <linux/init.h>
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#include <linux/ftrace.h>
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#include <asm/cacheflush.h>
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#ifdef CONFIG_DYNAMIC_FTRACE
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#define JAL 0x0c000000 /* jump & link: ip --> ra, jump to target */
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#define ADDR_MASK 0x03ffffff /* op_code|addr : 31...26|25 ....0 */
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#define jump_insn_encode(op_code, addr) \
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((unsigned int)((op_code) | (((addr) >> 2) & ADDR_MASK)))
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static unsigned int ftrace_nop = 0x00000000;
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static int ftrace_modify_code(unsigned long ip, unsigned int new_code)
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{
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*(unsigned int *)ip = new_code;
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flush_icache_range(ip, ip + 8);
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return 0;
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}
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static int lui_v1;
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static int jal_mcount;
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int ftrace_make_nop(struct module *mod,
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struct dyn_ftrace *rec, unsigned long addr)
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{
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unsigned int new;
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unsigned long ip = rec->ip;
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/* We have compiled module with -mlong-calls, but compiled the kernel
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* without it, we need to cope with them respectively. */
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if (ip & 0x40000000) {
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/* record it for ftrace_make_call */
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if (lui_v1 == 0)
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lui_v1 = *(unsigned int *)ip;
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/* lui v1, hi_16bit_of_mcount --> b 1f (0x10000004)
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* addiu v1, v1, low_16bit_of_mcount
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* move at, ra
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* jalr v1
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* nop
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* 1f: (ip + 12)
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*/
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new = 0x10000004;
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} else {
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/* record/calculate it for ftrace_make_call */
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if (jal_mcount == 0) {
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/* We can record it directly like this:
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* jal_mcount = *(unsigned int *)ip;
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* Herein, jump over the first two nop instructions */
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jal_mcount = jump_insn_encode(JAL, (MCOUNT_ADDR + 8));
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}
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/* move at, ra
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* jalr v1 --> nop
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*/
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new = ftrace_nop;
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}
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return ftrace_modify_code(ip, new);
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}
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static int modified; /* initialized as 0 by default */
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int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
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{
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unsigned int new;
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unsigned long ip = rec->ip;
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/* We just need to remove the "b ftrace_stub" at the fist time! */
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if (modified == 0) {
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modified = 1;
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ftrace_modify_code(addr, ftrace_nop);
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}
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/* ip, module: 0xc0000000, kernel: 0x80000000 */
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new = (ip & 0x40000000) ? lui_v1 : jal_mcount;
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return ftrace_modify_code(ip, new);
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}
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#define FTRACE_CALL_IP ((unsigned long)(&ftrace_call))
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int ftrace_update_ftrace_func(ftrace_func_t func)
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{
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unsigned int new;
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new = jump_insn_encode(JAL, (unsigned long)func);
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return ftrace_modify_code(FTRACE_CALL_IP, new);
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}
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int __init ftrace_dyn_arch_init(void *data)
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{
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/* The return code is retured via data */
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*(unsigned long *)data = 0;
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return 0;
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}
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#endif /* CONFIG_DYNAMIC_FTRACE */
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