Commit 538f19526e40ce7a5a296fad6a3121409c890adc
Committed by
Ralf Baechle
1 parent
e6299d2677
Exists in
master
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4 other branches
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>
Showing 6 changed files with 206 additions and 1 deletions Side-by-side Diff
arch/mips/Kconfig
... | ... | @@ -7,6 +7,8 @@ |
7 | 7 | select HAVE_ARCH_KGDB |
8 | 8 | select HAVE_FUNCTION_TRACER |
9 | 9 | select HAVE_FUNCTION_TRACE_MCOUNT_TEST |
10 | + select HAVE_DYNAMIC_FTRACE | |
11 | + select HAVE_FTRACE_MCOUNT_RECORD | |
10 | 12 | # Horrible source of confusion. Die, die, die ... |
11 | 13 | select EMBEDDED |
12 | 14 | select RTC_LIB if !MACH_LOONGSON |
arch/mips/include/asm/ftrace.h
... | ... | @@ -19,6 +19,15 @@ |
19 | 19 | extern void _mcount(void); |
20 | 20 | #define mcount _mcount |
21 | 21 | |
22 | +#ifdef CONFIG_DYNAMIC_FTRACE | |
23 | +static inline unsigned long ftrace_call_adjust(unsigned long addr) | |
24 | +{ | |
25 | + return addr; | |
26 | +} | |
27 | + | |
28 | +struct dyn_arch_ftrace { | |
29 | +}; | |
30 | +#endif /* CONFIG_DYNAMIC_FTRACE */ | |
22 | 31 | #endif /* __ASSEMBLY__ */ |
23 | 32 | #endif /* CONFIG_FUNCTION_TRACER */ |
24 | 33 | #endif /* _ASM_MIPS_FTRACE_H */ |
arch/mips/kernel/Makefile
... | ... | @@ -11,6 +11,7 @@ |
11 | 11 | time.o topology.o traps.o unaligned.o watch.o |
12 | 12 | |
13 | 13 | ifdef CONFIG_FUNCTION_TRACER |
14 | +CFLAGS_REMOVE_ftrace.o = -pg | |
14 | 15 | CFLAGS_REMOVE_early_printk.o = -pg |
15 | 16 | endif |
16 | 17 | |
... | ... | @@ -31,7 +32,7 @@ |
31 | 32 | obj-$(CONFIG_STACKTRACE) += stacktrace.o |
32 | 33 | obj-$(CONFIG_MODULES) += mips_ksyms.o module.o |
33 | 34 | |
34 | -obj-$(CONFIG_FUNCTION_TRACER) += mcount.o | |
35 | +obj-$(CONFIG_FUNCTION_TRACER) += mcount.o ftrace.o | |
35 | 36 | |
36 | 37 | obj-$(CONFIG_CPU_LOONGSON2) += r4k_fpu.o r4k_switch.o |
37 | 38 | obj-$(CONFIG_CPU_MIPS32) += r4k_fpu.o r4k_switch.o |
arch/mips/kernel/ftrace.c
1 | +/* | |
2 | + * Code for replacing ftrace calls with jumps. | |
3 | + * | |
4 | + * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com> | |
5 | + * Copyright (C) 2009 DSLab, Lanzhou University, China | |
6 | + * Author: Wu Zhangjin <wuzj@lemote.com> | |
7 | + * | |
8 | + * Thanks goes to Steven Rostedt for writing the original x86 version. | |
9 | + */ | |
10 | + | |
11 | +#include <linux/uaccess.h> | |
12 | +#include <linux/init.h> | |
13 | +#include <linux/ftrace.h> | |
14 | + | |
15 | +#include <asm/cacheflush.h> | |
16 | + | |
17 | +#ifdef CONFIG_DYNAMIC_FTRACE | |
18 | + | |
19 | +#define JAL 0x0c000000 /* jump & link: ip --> ra, jump to target */ | |
20 | +#define ADDR_MASK 0x03ffffff /* op_code|addr : 31...26|25 ....0 */ | |
21 | +#define jump_insn_encode(op_code, addr) \ | |
22 | + ((unsigned int)((op_code) | (((addr) >> 2) & ADDR_MASK))) | |
23 | + | |
24 | +static unsigned int ftrace_nop = 0x00000000; | |
25 | + | |
26 | +static int ftrace_modify_code(unsigned long ip, unsigned int new_code) | |
27 | +{ | |
28 | + *(unsigned int *)ip = new_code; | |
29 | + | |
30 | + flush_icache_range(ip, ip + 8); | |
31 | + | |
32 | + return 0; | |
33 | +} | |
34 | + | |
35 | +static int lui_v1; | |
36 | +static int jal_mcount; | |
37 | + | |
38 | +int ftrace_make_nop(struct module *mod, | |
39 | + struct dyn_ftrace *rec, unsigned long addr) | |
40 | +{ | |
41 | + unsigned int new; | |
42 | + unsigned long ip = rec->ip; | |
43 | + | |
44 | + /* We have compiled module with -mlong-calls, but compiled the kernel | |
45 | + * without it, we need to cope with them respectively. */ | |
46 | + if (ip & 0x40000000) { | |
47 | + /* record it for ftrace_make_call */ | |
48 | + if (lui_v1 == 0) | |
49 | + lui_v1 = *(unsigned int *)ip; | |
50 | + | |
51 | + /* lui v1, hi_16bit_of_mcount --> b 1f (0x10000004) | |
52 | + * addiu v1, v1, low_16bit_of_mcount | |
53 | + * move at, ra | |
54 | + * jalr v1 | |
55 | + * nop | |
56 | + * 1f: (ip + 12) | |
57 | + */ | |
58 | + new = 0x10000004; | |
59 | + } else { | |
60 | + /* record/calculate it for ftrace_make_call */ | |
61 | + if (jal_mcount == 0) { | |
62 | + /* We can record it directly like this: | |
63 | + * jal_mcount = *(unsigned int *)ip; | |
64 | + * Herein, jump over the first two nop instructions */ | |
65 | + jal_mcount = jump_insn_encode(JAL, (MCOUNT_ADDR + 8)); | |
66 | + } | |
67 | + | |
68 | + /* move at, ra | |
69 | + * jalr v1 --> nop | |
70 | + */ | |
71 | + new = ftrace_nop; | |
72 | + } | |
73 | + return ftrace_modify_code(ip, new); | |
74 | +} | |
75 | + | |
76 | +static int modified; /* initialized as 0 by default */ | |
77 | + | |
78 | +int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) | |
79 | +{ | |
80 | + unsigned int new; | |
81 | + unsigned long ip = rec->ip; | |
82 | + | |
83 | + /* We just need to remove the "b ftrace_stub" at the fist time! */ | |
84 | + if (modified == 0) { | |
85 | + modified = 1; | |
86 | + ftrace_modify_code(addr, ftrace_nop); | |
87 | + } | |
88 | + /* ip, module: 0xc0000000, kernel: 0x80000000 */ | |
89 | + new = (ip & 0x40000000) ? lui_v1 : jal_mcount; | |
90 | + | |
91 | + return ftrace_modify_code(ip, new); | |
92 | +} | |
93 | + | |
94 | +#define FTRACE_CALL_IP ((unsigned long)(&ftrace_call)) | |
95 | + | |
96 | +int ftrace_update_ftrace_func(ftrace_func_t func) | |
97 | +{ | |
98 | + unsigned int new; | |
99 | + | |
100 | + new = jump_insn_encode(JAL, (unsigned long)func); | |
101 | + | |
102 | + return ftrace_modify_code(FTRACE_CALL_IP, new); | |
103 | +} | |
104 | + | |
105 | +int __init ftrace_dyn_arch_init(void *data) | |
106 | +{ | |
107 | + /* The return code is retured via data */ | |
108 | + *(unsigned long *)data = 0; | |
109 | + | |
110 | + return 0; | |
111 | +} | |
112 | +#endif /* CONFIG_DYNAMIC_FTRACE */ |
arch/mips/kernel/mcount.S
... | ... | @@ -58,6 +58,33 @@ |
58 | 58 | move ra, AT |
59 | 59 | .endm |
60 | 60 | |
61 | +#ifdef CONFIG_DYNAMIC_FTRACE | |
62 | + | |
63 | +NESTED(ftrace_caller, PT_SIZE, ra) | |
64 | + .globl _mcount | |
65 | +_mcount: | |
66 | + b ftrace_stub | |
67 | + nop | |
68 | + lw t0, function_trace_stop | |
69 | + bnez t0, ftrace_stub | |
70 | + nop | |
71 | + | |
72 | + MCOUNT_SAVE_REGS | |
73 | + | |
74 | + move a0, ra /* arg1: next ip, selfaddr */ | |
75 | + .globl ftrace_call | |
76 | +ftrace_call: | |
77 | + nop /* a placeholder for the call to a real tracing function */ | |
78 | + move a1, AT /* arg2: the caller's next ip, parent */ | |
79 | + | |
80 | + MCOUNT_RESTORE_REGS | |
81 | + .globl ftrace_stub | |
82 | +ftrace_stub: | |
83 | + RETURN_BACK | |
84 | + END(ftrace_caller) | |
85 | + | |
86 | +#else /* ! CONFIG_DYNAMIC_FTRACE */ | |
87 | + | |
61 | 88 | NESTED(_mcount, PT_SIZE, ra) |
62 | 89 | lw t0, function_trace_stop |
63 | 90 | bnez t0, ftrace_stub |
... | ... | @@ -81,6 +108,8 @@ |
81 | 108 | ftrace_stub: |
82 | 109 | RETURN_BACK |
83 | 110 | END(_mcount) |
111 | + | |
112 | +#endif /* ! CONFIG_DYNAMIC_FTRACE */ | |
84 | 113 | |
85 | 114 | .set at |
86 | 115 | .set reorder |
scripts/recordmcount.pl
... | ... | @@ -295,6 +295,58 @@ |
295 | 295 | $ld .= " -m elf64_sparc"; |
296 | 296 | $cc .= " -m64"; |
297 | 297 | $objcopy .= " -O elf64-sparc"; |
298 | +} elsif ($arch eq "mips") { | |
299 | + # To enable module support, we need to enable the -mlong-calls option | |
300 | + # of gcc for module, after using this option, we can not get the real | |
301 | + # offset of the calling to _mcount, but the offset of the lui | |
302 | + # instruction or the addiu one. herein, we record the address of the | |
303 | + # first one, and then we can replace this instruction by a branch | |
304 | + # instruction to jump over the profiling function to filter the | |
305 | + # indicated functions, or swith back to the lui instruction to trace | |
306 | + # them, which means dynamic tracing. | |
307 | + # | |
308 | + # c: 3c030000 lui v1,0x0 | |
309 | + # c: R_MIPS_HI16 _mcount | |
310 | + # c: R_MIPS_NONE *ABS* | |
311 | + # c: R_MIPS_NONE *ABS* | |
312 | + # 10: 64630000 daddiu v1,v1,0 | |
313 | + # 10: R_MIPS_LO16 _mcount | |
314 | + # 10: R_MIPS_NONE *ABS* | |
315 | + # 10: R_MIPS_NONE *ABS* | |
316 | + # 14: 03e0082d move at,ra | |
317 | + # 18: 0060f809 jalr v1 | |
318 | + # | |
319 | + # for the kernel: | |
320 | + # | |
321 | + # 10: 03e0082d move at,ra | |
322 | + # 14: 0c000000 jal 0 <loongson_halt> | |
323 | + # 14: R_MIPS_26 _mcount | |
324 | + # 14: R_MIPS_NONE *ABS* | |
325 | + # 14: R_MIPS_NONE *ABS* | |
326 | + # 18: 00020021 nop | |
327 | + if ($is_module eq "0") { | |
328 | + $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$"; | |
329 | + } else { | |
330 | + $mcount_regex = "^\\s*([0-9a-fA-F]+): R_MIPS_HI16\\s+_mcount\$"; | |
331 | + } | |
332 | + $objdump .= " -Melf-trad".$endian."mips "; | |
333 | + | |
334 | + if ($endian eq "big") { | |
335 | + $endian = " -EB "; | |
336 | + $ld .= " -melf".$bits."btsmip"; | |
337 | + } else { | |
338 | + $endian = " -EL "; | |
339 | + $ld .= " -melf".$bits."ltsmip"; | |
340 | + } | |
341 | + | |
342 | + $cc .= " -mno-abicalls -fno-pic -mabi=" . $bits . $endian; | |
343 | + $ld .= $endian; | |
344 | + | |
345 | + if ($bits == 64) { | |
346 | + $function_regex = | |
347 | + "^([0-9a-fA-F]+)\\s+<(.|[^\$]L.*?|\$[^L].*?|[^\$][^L].*?)>:"; | |
348 | + $type = ".dword"; | |
349 | + } | |
298 | 350 | } elsif ($arch eq "microblaze") { |
299 | 351 | # Microblaze calls '_mcount' instead of plain 'mcount'. |
300 | 352 | $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$"; |