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author | Wu Zhangjin <wuzhangjin@gmail.com> | 2009-11-20 20:34:32 +0800 |
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committer | Ralf Baechle <ralf@linux-mips.org> | 2009-12-17 01:57:23 +0000 |
commit | 538f19526e40ce7a5a296fad6a3121409c890adc (patch) | |
tree | bbdf5a55a08dafaf2497a241703e944563241ddc /arch | |
parent | e6299d2677e600f6a0bf93bbb89f20d3de5252de (diff) | |
download | linux-538f19526e40ce7a5a296fad6a3121409c890adc.tar.gz linux-538f19526e40ce7a5a296fad6a3121409c890adc.tar.bz2 linux-538f19526e40ce7a5a296fad6a3121409c890adc.zip |
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>
Diffstat (limited to 'arch')
-rw-r--r-- | arch/mips/Kconfig | 2 | ||||
-rw-r--r-- | arch/mips/include/asm/ftrace.h | 9 | ||||
-rw-r--r-- | arch/mips/kernel/Makefile | 3 | ||||
-rw-r--r-- | arch/mips/kernel/ftrace.c | 112 | ||||
-rw-r--r-- | arch/mips/kernel/mcount.S | 29 |
5 files changed, 154 insertions, 1 deletions
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig index d203dbfa8037..af6940c5b272 100644 --- a/arch/mips/Kconfig +++ b/arch/mips/Kconfig @@ -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 diff --git a/arch/mips/include/asm/ftrace.h b/arch/mips/include/asm/ftrace.h index 5f8ebcf9fa61..7094a40b96d8 100644 --- a/arch/mips/include/asm/ftrace.h +++ b/arch/mips/include/asm/ftrace.h @@ -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 */ diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile index 1340ba3dd38d..8dda21463226 100644 --- a/arch/mips/kernel/Makefile +++ b/arch/mips/kernel/Makefile @@ -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 diff --git a/arch/mips/kernel/ftrace.c b/arch/mips/kernel/ftrace.c new file mode 100644 index 000000000000..5459a7838370 --- /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 <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 */ diff --git a/arch/mips/kernel/mcount.S b/arch/mips/kernel/mcount.S index cbb45edad464..ffc425979d4f 100644 --- a/arch/mips/kernel/mcount.S +++ b/arch/mips/kernel/mcount.S @@ -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 |