Messages in this thread | | | Date | Fri, 14 Mar 2014 13:45:13 +0900 | From | AKASHI Takahiro <> | Subject | Re: [PATCH v6 4/7] arm64: Add ftrace support |
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On 03/14/2014 02:08 AM, Will Deacon wrote: > On Thu, Mar 13, 2014 at 10:13:47AM +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. > > [...]
You seem not to like this statement :-)
>> diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S >> new file mode 100644 >> index 0000000..0ac31c8 >> --- /dev/null >> +++ b/arch/arm64/kernel/entry-ftrace.S >> @@ -0,0 +1,175 @@ >> +/* >> + * arch/arm64/kernel/entry-ftrace.S >> + * >> + * 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. >> + */ >> + >> +#include <linux/linkage.h> >> +#include <asm/ftrace.h> >> +#include <asm/insn.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 instrumented function at any time by winding up call stack >> + * 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 in _mcount(): >> + * >> + * current sp/fp => 0:+-----+ >> + * in _mcount() | x29 | -> instrumented function's fp >> + * +-----+ >> + * | x30 | -> _mcount()'s lr (= instrumented function's pc) >> + * old sp => +16:+-----+ >> + * when instrumented | | >> + * function calls | ... | >> + * _mcount() | | >> + * | | >> + * instrumented => +xx:+--- --+ >> + * function's fp | x29 | -> parent's fp >> + * +-----+ >> + * | x30 | -> instrumented function's lr (= parent's pc) >> + * +-----+ >> + * | ... | > > I guess it's just the diff that's misaligning your ASCII art here?
Yes, I think so. Misaligned due to "tab"
>> +/* >> + * void return_to_handler(void) >> + * >> + * Run ftrace_return_to_handler() before going back to parent. >> + * @fp is checked against the value passed by ftrace_graph_caller() >> + * only when CONFIG_FUNCTION_GRAPH_FP_TEST is enabled.a >> + */ >> + .global return_to_handler >> +return_to_handler: > > ENTRY(return_to_handler)
Fix it.
>> + str x0, [sp, #-16]! >> + mov x0, x29 // parent's fp >> + bl ftrace_return_to_handler// addr = ftrace_return_to_hander(fp); >> + mov x30, x0 // restore the original return address >> + ldr x0, [sp], #16 >> + ret > > and an ENDPROC here.
Fix it. But please note that this (return_to_handler) is not a real function. Declaring it as ENDPROC is not very useful.
>> +#endif /* CONFIG_FUNCTION_GRAPH_TRACER */ >> diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c >> new file mode 100644 >> index 0000000..a559ab8 >> --- /dev/null >> +++ b/arch/arm64/kernel/ftrace.c >> @@ -0,0 +1,64 @@ >> +/* >> + * arch/arm64/kernel/ftrace.c >> + * >> + * 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. >> + */ >> + >> +#include <linux/ftrace.h> >> +#include <linux/swab.h> >> +#include <linux/uaccess.h> >> + >> +#include <asm/cacheflush.h> >> +#include <asm/ftrace.h> >> +#include <asm/insn.h> >> + >> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER >> +/* >> + * function_graph tracer expects ftrace_return_to_handler() to be called >> + * on the way back to parent. For this purpose, this function is called >> + * in _mcount() or ftrace_caller() to replace return address (*parent) on >> + * the call stack to return_to_handler. >> + * >> + * Note that @frame_pointer is used only for sanity check later. >> + */ >> +void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr, >> + unsigned long frame_pointer) >> +{ >> + unsigned long return_hooker = (unsigned long)&return_to_handler; >> + unsigned long old; >> + struct ftrace_graph_ent trace; >> + int err; >> + >> + if (unlikely(atomic_read(¤t->tracing_graph_pause))) >> + return; >> + >> + /* >> + * Note: >> + * No protection against faulting at *parent, which may be seen >> + * on other archs. It's unlikely on AArch64. >> + */ >> + old = *parent; >> + *parent = return_hooker; > > return_hook? People might take it personally otherwise ;)
I didn't know what "(return) hooker" means. Anyway, leave it as it is after you and Steven's discussion.
>> + trace.func = self_addr; > > in kernel/ftrace/ftrace.c there's an smb_wmb() between setting up > tracing_graph_pause and setting the ret_stack with a comment saying: > > /* Make sure the tasks see the -1 first: */ > > Why don't we have a corresponding read-barrier here?
I think Steven answered it.
-Takahiro AKASHI
> Will >
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