Re: [RFC PATCH -next v2 3/4] arm64/ftrace: support dynamically allocated trampolines

Steven Rostedt
2022-05-25T13:44:38Z

On Wed, 25 May 2022 13:17:30 +0100
Mark Rutland <mark.rutland@arm.com> wrote:

> For arm64 I'd like to make this static, and have ftrace *always* capture a
> minimal set of ftrace_regs, which would be:
>
> X0 to X8 inclusive
> SP
> PC
> LR
> FP
>
> Since X0 to X8 + SP is all that we need for arguments and return values (per
> the calling convention we use), and PC+LR+FP gives us everything we need for
> unwinding and live patching.
>
> I *might* want to add x18 to that when SCS is enabled, but I'm not immediately
> sure.

Does arm64 have HAVE_DYNAMIC_FTRACE_WITH_ARGS enabled? If so, then having
the normal ftrace call back save the above so that all functions have it
available would be useful.

-- Steve