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