On Mon, Dec 18, 2023 at 10:11:44PM +0900, Masami Hiramatsu (Google) wrote:
> From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
>
> To clarify what will be expected on ftrace_regs, add a comment to the
> architecture independent definition of the ftrace_regs.
>
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
Mark.
> ---
> Changes in v3:
> - Add instruction pointer
> Changes in v2:
> - newly added.
> ---
> include/linux/ftrace.h | 26 ++++++++++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index e8921871ef9a..8b48fc621ea0 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -118,6 +118,32 @@ extern int ftrace_enabled;
>
> #ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
>
> +/**
> + * ftrace_regs - ftrace partial/optimal register set
> + *
> + * ftrace_regs represents a group of registers which is used at the
> + * function entry and exit. There are three types of registers.
> + *
> + * - Registers for passing the parameters to callee, including the stack
> + * pointer. (e.g. rcx, rdx, rdi, rsi, r8, r9 and rsp on x86_64)
> + * - Registers for passing the return values to caller.
> + * (e.g. rax and rdx on x86_64)
> + * - Registers for hooking the function call and return including the
> + * frame pointer (the frame pointer is architecture/config dependent)
> + * (e.g. rip, rbp and rsp for x86_64)
> + *
> + * Also, architecture dependent fields can be used for internal process.
> + * (e.g. orig_ax on x86_64)
> + *
> + * On the function entry, those registers will be restored except for
> + * the stack pointer, so that user can change the function parameters
> + * and instruction pointer (e.g. live patching.)
> + * On the function exit, only registers which is used for return values
> + * are restored.
> + *
> + * NOTE: user *must not* access regs directly, only do it via APIs, because
> + * the member can be changed according to the architecture.
> + */
> struct ftrace_regs {
> struct pt_regs regs;
> };
>
