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_enterstp x29, x30, [sp, #-48]!.endmCan 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