Re: [PATCH v14 04/19] function_graph: Replace fgraph_ret_regs with ftrace_regs

On Tue, 1 Oct 2024 19:32:34 -0400
Steven Rostedt [off-list ref] wrote:

On Wed, 2 Oct 2024 08:10:37 +0900
Masami Hiramatsu (Google) [off-list ref] wrote:

quoted

quoted

I may add some compiler hacks to enforce this. Something like:

struct ftrace_regs {
	void *nothing_to_see_here;
};  

Yeah, OK. But sizeof(fregs) may be changed. (Shouldn't we do too?)

Honestly, I don't think anything should be doing a sizeof(struct ftrace_regs)

Heck, perhaps we should make it totally zero!

  struct ftrace_regs {
	long nothing_here[];
  };

If someone needs to allocate, then we could provide a:

	ftrace_regs_size()

helper function.

Ah, Indeed.

quoted

quoted

And then change the arch code to be something like:

// in arch/arm64/include/asm/ftrace.h:

struct arch_ftrace_regs {
        /* x0 - x8 */
        unsigned long regs[9];

#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
        unsigned long direct_tramp;
#else
        unsigned long __unused;
#endif

        unsigned long fp;
        unsigned long lr;

        unsigned long sp;
        unsigned long pc;
};  

And if it is pt_regs compatible, 

#define arch_ftrace_regs pt_regs

?

Only if it is fully pt_regs compatible.

Yeah, OK, this is good idea.

Thank you,

-- Steve

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