Messages in this thread Patch in this message | | | Date | Thu, 13 Mar 2014 17:08:34 +0000 | From | Will Deacon <> | Subject | Re: [PATCH v6 4/7] arm64: Add ftrace support |
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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.
[...]
> 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?
> +/* > + * 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. > + */ > + .global return_to_handler > +return_to_handler:
ENTRY(return_to_handler)
> + 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.
> +#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 ;)
> + 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?
Will
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