Title: [6736] trunk/Documentation/trace/ftrace-implementation.txt: more mainline feedback
- Revision
- 6736
- Author
- vapier
- Date
- 2009-06-16 02:01:43 -0500 (Tue, 16 Jun 2009)
Log Message
more mainline feedback
Modified Paths
Diff
Modified: trunk/Documentation/trace/ftrace-implementation.txt (6735 => 6736)
--- trunk/Documentation/trace/ftrace-implementation.txt 2009-06-16 07:01:25 UTC (rev 6735)
+++ trunk/Documentation/trace/ftrace-implementation.txt 2009-06-16 07:01:43 UTC (rev 6736)
@@ -21,8 +21,8 @@
TRACE_IRQFLAGS_SUPPORT - implement include/asm/irqflags.h
-HAVE_FUNCTION_GRAPH_TRACER
---------------------------
+HAVE_FUNCTION_TRACER
+--------------------
You will need to implement the mcount and the ftrace_stub functions.
@@ -37,9 +37,11 @@
Keep in mind that the ABI that is in effect inside of the mcount function is
*highly* architecture/toolchain specific. We cannot help you in this regard,
sorry. Dig up some old documentation and/or find someone more familiar than
-you to bang ideas off of. Typically, register usage/clobbering is a major
-problem here. You might also want to look at how glibc has implemented the
-mcount function for your architecture. It might be (semi-)relevant.
+you to bang ideas off of. Typically, register usage (argument/scratch/etc...)
+is a major issue at this point, especially in relation to the location of the
+mcount call (before/after function prologue). You might also want to look at
+how glibc has implemented the mcount function for your architecture. It might
+be (semi-)relevant.
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,
@@ -82,7 +84,7 @@
do_trace:
- /* save all state needed by the ABI */
+ /* save all state needed by the ABI (see paragraph above) */
unsigned long frompc = ...;
unsigned long selfpc = <return address> - MCOUNT_INSN_SIZE;
@@ -184,12 +186,14 @@
Here is the pseudo code for the new return_to_handler assembly function. Note
that the ABI that applies here is different from what applies to the mcount
-code. Here you are returning from a function, so you might be able to skimp
-on things saved/restored.
+code. Since you are returning from a function (after the epilogue), you might
+be able to skimp on things saved/restored (usually just registers used to pass
+return values).
+
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
void return_to_handler(void)
{
- /* save all state needed by the ABI */
+ /* save all state needed by the ABI (see paragraph above) */
void (*original_return_point)(void) = ftrace_return_to_handler();
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