Re: [PATCH v18 01/17] fgraph: Pass ftrace_regs to entryfunc

Steven Rostedt
2024-10-31T19:52:31Z

On Sat, 26 Oct 2024 13:35:30 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:

> 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.

> @@ -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??

-- Steve

> #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) {