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Subject[PATCH 5/5] tracing/documentation: Cover new frame pointer semantics
From: Mike Frysinger <vapier@gentoo.org>

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: Mike Frysinger <vapier@gentoo.org>
LKML-Reference: <1264165967-18938-1-git-send-email-vapier@gentoo.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
Documentation/trace/ftrace-design.txt | 26 +++++++++++++++++++++++---
kernel/trace/Kconfig | 4 +---
2 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/Documentation/trace/ftrace-design.txt b/Documentation/trace/ftrace-design.txt
index 239f14b..6a5a579 100644
--- a/Documentation/trace/ftrace-design.txt
+++ b/Documentation/trace/ftrace-design.txt
@@ -1,5 +1,6 @@
function tracer guts
====================
+ By Mike Frysinger

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

unsigned long *frompc = &...;
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 */
}
#endif

-For information on how to implement prepare_ftrace_return(), simply look at
-the x86 version. The only architecture-specific piece in it is the setup of
+For information on how to implement prepare_ftrace_return(), simply look at the
+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
across architectures.

@@ -205,6 +208,23 @@ void return_to_handler(void)
#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
---------------------

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 6c22d8a..60e2ce0 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -27,9 +27,7 @@ config HAVE_FUNCTION_GRAPH_TRACER
config HAVE_FUNCTION_GRAPH_FP_TEST
bool
help
- 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.
+ See Documentation/trace/ftrace-design.txt

config HAVE_FUNCTION_TRACE_MCOUNT_TEST
bool
--
1.6.5



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