On Thu, 31 Oct 2024 15:53:24 -0400
Steven Rostedt [off-list ref] wrote:

On Sat, 26 Oct 2024 13:35:30 +0900
"Masami Hiramatsu (Google)" [off-list ref] wrote:

quoted

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Pass ftrace_regs to the fgraph_ops::entryfunc(). If ftrace_regs is not
available, it passes a NULL instead. User callback function can access
some registers (including return address) via this ftrace_regs.

Note that the ftrace_regs can be NULL when the arch does NOT define:
HAVE_DYNAMIC_FTRACE_WITH_ARGS or HAVE_DYNAMIC_FTRACE_WITH_REGS.
More specifically, if HAVE_DYNAMIC_FTRACE_WITH_REGS is defined but
not the HAVE_DYNAMIC_FTRACE_WITH_ARGS, and the ftrace ops used to
register the function callback does not set FTRACE_OPS_FL_SAVE_REGS.
In this case, ftrace_regs can be NULL in user callback.

If HAVE_DYNAMIC_FTRACE_WITH_REGS is defined but not
HAVE_DYNAMIC_FTRACE_WITH_ARGS is not, then the callback will have regs defined.

quoted

@@ -977,7 +980,7 @@ unsigned long ftrace_graph_ret_addr(struct task_struct *task, int *idx,
 
 static struct ftrace_ops graph_ops = {
 	.func			= ftrace_graph_func,
-	.flags			= FTRACE_OPS_GRAPH_STUB,
+	.flags			= FTRACE_OPS_GRAPH_STUB | FTRACE_OPS_FL_SAVE_ARGS,

Enabling FTRACE_OPS_FL_SAVE_ARGS will pass full regs in that case. Are you
just saying in the change log that this is what you did? As it currently
reads, it sounds like a fgraph user needs to add FTRACE_OPS_FL_SAVE_REGS??

Ah, good catch! It should put the flag only when HAVE_DYNAMIC_FTRACE_WITH_ARGS
is enabled.

static struct ftrace_ops graph_ops = {
	.func			= ftrace_graph_func,
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
	.flags			= FTRACE_OPS_GRAPH_STUB | FTRACE_OPS_FL_SAVE_ARGS,
#elif defined(CONFIG_DYNAMIC_FTRACE_WITH_ARGS)
	.flags			= FTRACE_OPS_GRAPH_STUB | FTRACE_OPS_FL_SAVE_REGS,
#else
	.flags			= FTRACE_OPS_GRAPH_STUB,
#endif

This will save fregs or regs or NULL according to the configuration.

-- Steve

quoted

 #ifdef FTRACE_GRAPH_TRAMP_ADDR
 	.trampoline		= FTRACE_GRAPH_TRAMP_ADDR,
 	/* trampoline_size is only needed for dynamically allocated tramps */

@@ -987,7 +990,8 @@ static struct ftrace_ops graph_ops = {
 void fgraph_init_ops(struct ftrace_ops *dst_ops,
 		     struct ftrace_ops *src_ops)
 {
-	dst_ops->flags = FTRACE_OPS_FL_PID | FTRACE_OPS_GRAPH_STUB;
+	dst_ops->flags = FTRACE_OPS_FL_PID | FTRACE_OPS_GRAPH_STUB |
+			 FTRACE_OPS_FL_SAVE_ARGS;
 
 #ifdef CONFIG_DYNAMIC_FTRACE
 	if (src_ops) {

-- 
Masami Hiramatsu (Google) [off-list ref]