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Message-Id: <1244623722-6325-2-git-send-email-vapier@gentoo.org> Date: Wed, 10 Jun 2009 04:48:42 -0400 From: Mike Frysinger <vapier@...too.org> To: Steven Rostedt <rostedt@...dmis.org> Cc: linux-kernel@...r.kernel.org Subject: [PATCH 2/2] ftrace: document basic ftracer/ftracer graph needs While implementing ftracer and ftracer graph support, I found the exact arch implementation details to be a bit lacking (and my x86 foo ain't great). So after pounding out support for the Blackfin arch, document the requirements. Signed-off-by: Mike Frysinger <vapier@...too.org> --- Documentation/trace/ftrace.txt | 7 ++++++ kernel/trace/Kconfig | 43 ++++++++++++++++++++++++++++++++++++++++ 2 files changed, 50 insertions(+), 0 deletions(-) diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt index 5ad2ded..e9f0527 100644 --- a/Documentation/trace/ftrace.txt +++ b/Documentation/trace/ftrace.txt @@ -27,6 +27,13 @@ disabled, and more (ftrace allows for tracer plugins, which means that the list of tracers can always grow). +Implementation Details +---------------------- + +See kernel/trace/Kconfig for details about different options and +the required architecture pieces. + + The File System --------------- diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig index 417d198..be936c9 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -14,9 +14,46 @@ config HAVE_FTRACE_NMI_ENTER config HAVE_FUNCTION_TRACER bool + help + Implement support for the _mcount() function (or whatever your + toolchain names it), and the ftrace_stub function (which only + does a return). + + The _mcount() function should check the function pointer + ftrace_trace_function to see if it is set to ftrace_stub. If + it is, there is nothing for you to do -- return. If it isn't, + then call it the same way the _mcount() function normally calls + __mcount_internal() -- the first argument is the "frompc" while + the second argument is the "selfpc" (adjusted to remove the size + of the embedded _mcount() call). + + For example, if the function foo() calls bar(), when the bar() + function calls _mcount(), the arguments to the tracer are: + "frompc" - the address bar() will use to return to foo() + "selfpc" - the address bar() (with _mcount() size adjustment) config HAVE_FUNCTION_GRAPH_TRACER bool + help + Update your _mcount() function to check the function pointers + ftrace_graph_return (compare to ftrace_stub) and ftrace_graph_entry + (compare to ftrace_graph_entry_stub). If either of those are not + set to the relevant stub function, call the arch-specific function + ftrace_graph_caller which in turn calls the arch-specific function + prepare_ftrace_return. + + The arguments to prepare_ftrace_return() are slightly different. + The first argument will instead be a pointer to the "frompc" -- + typically located in the stack. This allows the function to + hijack the return address temporarily to have it point to the + arch-specific function return_to_handler(). For exact details of + how to implement prepare_ftrace_return(), consult an existing port. + It is fairly straight forward C code. + + The return_to_handler() function is simple as well. Have it call + the common ftrace_return_to_handler() function. The return value + is the original return address, so restore this to the right place + and return. config HAVE_FUNCTION_TRACE_MCOUNT_TEST bool @@ -25,11 +62,17 @@ config HAVE_FUNCTION_TRACE_MCOUNT_TEST variable at the mcount call site. Otherwise, this variable is tested by the called function. + It is of course optional for arches, but does improve performance + a bit as it prevents constant state saving and call overhead when + the function tracer is actually disabled. + config HAVE_DYNAMIC_FTRACE bool config HAVE_FTRACE_MCOUNT_RECORD bool + help + See scripts/recordmcount.pl for more info. config HAVE_HW_BRANCH_TRACER bool -- 1.6.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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