path: root/Documentation/trace
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authorMike Frysinger <vapier@gentoo.org>2010-01-22 08:12:47 -0500
committerSteven Rostedt <rostedt@goodmis.org>2010-01-26 17:00:39 -0500
commit03688970347bfea32823953a7ce5886d1713205f (patch)
tree7ae2cc539b20b0a621d4a11f335f96de619ecfcb /Documentation/trace
parent6993b1bb1e62367f500789835a1f747e12259f07 (diff)
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: Mike Frysinger <vapier@gentoo.org> LKML-Reference: <1264165967-18938-1-git-send-email-vapier@gentoo.org> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'Documentation/trace')
1 files changed, 23 insertions, 3 deletions
diff --git a/Documentation/trace/ftrace-design.txt b/Documentation/trace/ftrace-design.txt
index 239f14b2b55..6a5a579126b 100644
--- a/Documentation/trace/ftrace-design.txt
+++ b/Documentation/trace/ftrace-design.txt
@@ -1,5 +1,6 @@
function tracer guts
+ By Mike Frysinger
@@ -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 */
-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)
+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.