Re: [PATCH v3 4/8] fprobe: rethook: Use ftrace_regs in fprobe exit handler and rethook

[Florent Revest <revest@xxxxxxxxxxxx>]

On Sat, Aug 12, 2023 at 7:37 AM Masami Hiramatsu (Google)
<mhiramat@xxxxxxxxxx> wrote:
>
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index 976fd594b446..d56304276318 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -57,6 +57,13 @@ config HAVE_DYNAMIC_FTRACE_WITH_ARGS
>          This allows for use of ftrace_regs_get_argument() and
>          ftrace_regs_get_stack_pointer().
>
> +config HAVE_PT_REGS_TO_FTRACE_REGS_CAST
> +       bool
> +       help
> +        If this is set, the memory layout of the ftrace_regs data structure
> +        is the same as the pt_regs. So the pt_regs is possible to be casted
> +        to ftrace_regs.

What would you think of introducing a:

#ifdef HAVE_PT_REGS_TO_FTRACE_REGS_CAST
static_assert(sizeof(struct pt_regs) == sizeof(struct ftrace_regs);
#endif // HAVE_PT_REGS_TO_FTRACE_REGS_CAST

somewhere in ftrace.h just as a small extra safety net ? It doesn't
exactly guarantee all we want but it should give an early warning of
mistakes.