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Commit 03688970 authored by Mike Frysinger's avatar Mike Frysinger Committed by Steven Rostedt
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tracing/documentation: Cover new frame pointer semantics 



Update the graph tracer examples to cover the new frame pointer semantics
(in terms of passing it along).  Move the HAVE_FUNCTION_GRAPH_FP_TEST docs
out of the Kconfig, into the right place, and expand on the details.

Signed-off-by: default avatarMike Frysinger <vapier@gentoo.org>
LKML-Reference: <1264165967-18938-1-git-send-email-vapier@gentoo.org>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 6993b1bb

Documentation/trace/ftrace-design.txt

+23 −3
Original line number Original line Diff line number Diff line 
		function tracer guts

		function tracer guts

		====================

		====================

		By Mike Frysinger





Introduction

Introduction

------------

------------
@@ -173,14 +174,16 @@ void ftrace_graph_caller(void) 




	unsigned long *frompc = &...;

	unsigned long *frompc = &...;

	unsigned long selfpc = <return address> - MCOUNT_INSN_SIZE;

	unsigned long selfpc = <return address> - MCOUNT_INSN_SIZE;

	prepare_ftrace_return(frompc, selfpc);

	/* passing frame pointer up is optional -- see below */

	prepare_ftrace_return(frompc, selfpc, frame_pointer);





	/* restore all state needed by the ABI */

	/* restore all state needed by the ABI */

}

}

#endif

#endif





For information on how to implement prepare_ftrace_return(), simply look at

For information on how to implement prepare_ftrace_return(), simply look at the

the x86 version.  The only architecture-specific piece in it is the setup of

x86 version (the frame pointer passing is optional; see the next section for

more information).  The only architecture-specific piece in it is the setup of

the fault recovery table (the asm(...) code).  The rest should be the same

the fault recovery table (the asm(...) code).  The rest should be the same

across architectures.

across architectures.
@@ -205,6 +208,23 @@ void return_to_handler(void) 
#endif

#endif









HAVE_FUNCTION_GRAPH_FP_TEST

---------------------------



An arch may pass in a unique value (frame pointer) to both the entering and

exiting of a function.  On exit, the value is compared and if it does not

match, then it will panic the kernel.  This is largely a sanity check for bad

code generation with gcc.  If gcc for your port sanely updates the frame

pointer under different opitmization levels, then ignore this option.



However, adding support for it isn't terribly difficult.  In your assembly code

that calls prepare_ftrace_return(), pass the frame pointer as the 3rd argument.

Then in the C version of that function, do what the x86 port does and pass it

along to ftrace_push_return_trace() instead of a stub value of 0.



Similarly, when you call ftrace_return_to_handler(), pass it the frame pointer.





HAVE_FTRACE_NMI_ENTER

HAVE_FTRACE_NMI_ENTER

---------------------

---------------------

kernel/trace/Kconfig

+1 −3
Original line number Original line Diff line number Diff line
@@ -27,9 +27,7 @@ config HAVE_FUNCTION_GRAPH_TRACER 
config HAVE_FUNCTION_GRAPH_FP_TEST

config HAVE_FUNCTION_GRAPH_FP_TEST

	bool

	bool

	help

	help

	 An arch may pass in a unique value (frame pointer) to both the

	  See Documentation/trace/ftrace-design.txt

	 entering and exiting of a function. On exit, the value is compared

	 and if it does not match, then it will panic the kernel.





config HAVE_FUNCTION_TRACE_MCOUNT_TEST

config HAVE_FUNCTION_TRACE_MCOUNT_TEST

	bool

	bool