Messages in this thread | | | Date | Wed, 19 Feb 2014 19:46:53 +0900 | From | AKASHI Takahiro <> | Subject | Re: [PATCH v3 1/6] arm64: Add ftrace support |
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On 02/18/2014 03:12 AM, Will Deacon wrote: > On Fri, Feb 07, 2014 at 10:18:51AM +0000, AKASHI Takahiro wrote: >> This patch implements arm64 specific part to support function tracers, >> such as function (CONFIG_FUNCTION_TRACER), function_graph >> (CONFIG_FUNCTION_GRAPH_TRACER) and function profiler >> (CONFIG_FUNCTION_PROFILER). >> >> With 'function' tracer, all the functions in the kernel are traced with >> timestamps in ${sysfs}/tracing/trace. If function_graph tracer is >> specified, call graph is generated. >> >> The kernel must be compiled with -pg option so that _mcount() is inserted >> at the beginning of functions. This function is called on every function's >> entry as long as tracing is enabled. >> In addition, function_graph tracer also needs to be able to probe function's >> exit. ftrace_graph_caller() & return_to_handler do this by faking link >> register's value to intercept function's return path. >> >> More details on architecture specific requirements are described in >> Documentation/trace/ftrace-design.txt. > > [...] > >> diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h >> new file mode 100644 >> index 0000000..0d5dfdb >> --- /dev/null >> +++ b/arch/arm64/include/asm/ftrace.h >> @@ -0,0 +1,23 @@ >> +/* >> + * arch/arm64/include/asm/ftrace.h >> + * >> + * Copyright (C) 2013 Linaro Limited >> + * Author: AKASHI Takahiro <takahiro.akashi@linaro.org> >> + * >> + * This program is free software; you can redistribute it and/or modify >> + * it under the terms of the GNU General Public License version 2 as >> + * published by the Free Software Foundation. >> + */ >> +#ifndef __ASM_FTRACE_H >> +#define __ASM_FTRACE_H >> + >> +#ifdef CONFIG_FUNCTION_TRACER >> +#define MCOUNT_ADDR ((unsigned long)_mcount) >> +#define MCOUNT_INSN_SIZE 4 /* sizeof mcount call */ > > You can use AARCH64_INSN_SIZE here.
OK, but MCOUNT_INSN_SIZE can't be removed here because it is also used in kernel/trace/ftrace.c. So I will redefine it as #define MCOUNT_INSN_SIZE AARCH64_INSN_SIZE
In this case, I need to add __ASSEMBLY__ in asm/insn.h because asm/ftrace.h (and so asm/insn.h) is included in entry-ftrace.S.
Is it OK?
>> +#include <linux/linkage.h> >> +#include <asm/ftrace.h> >> + >> +/* >> + * Gcc with -pg will put the following code in the beginning of each function: >> + * mov x0, x30 >> + * bl _mcount >> + * [function's body ...] >> + * "bl _mcount" may be replaced to "bl ftrace_caller" or NOP if dynamic >> + * ftrace is enabled. >> + * >> + * Please note that x0 as an argument will not be used here because we can >> + * get lr(x30) of insturmented function at any time by winding up call stack > > instrumented
I will fix two occurences of "insturmented" :-) Just a question: Is there any better word than "instrument"?
>> + * as long as the kernel is compiled without -fomit-frame-pointer. >> + * (or CONFIG_FRAME_POINTER, this is forced on arm64) >> + * >> + * stack layout after mcount_enter: >> + * >> + * 0 ---------------------------------------- sp of _mcount() >> + * x29: fp of instrumented function fp is not winded >> + * -------------------- >> + * x30: lr of _mcount() (= instrumented function's pc) >> + * +16 ---------------------------------------- sp of instrumented function >> + * >> + * .... >> + * >> + * +xx ---------------------------------------- fp of instrumented function >> + * x29: fp of parent >> + * -------------------- >> + * x30: lr of insturmented function (= parent's pc) >> + * -------------------- >> + * xxx >> + */ >> + >> + .macro mcount_enter >> + stp x29, x30, [sp, #-48]! >> + .endm > > Can you elaborate in your comment about where this 48 comes from please? I > can't join it up with your ascii art.
Right. It should be -16 as shown in the stack layout. When I removed an operation of saving/restoring x0-x3 at v3 patch, this value should also have been changed.
-Takahiro AKASHI
> Will >
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