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

Steven Rostedt
2024-10-01T23:31:45Z

On Wed, 2 Oct 2024 08:10:37 +0900
Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:
> >
> > 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.

>
> >
> > 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.

-- Steve