linux-kernel - Re: [PATCH 0/4] s390: DYNAMIC_FTRACE_WITH_DIRECT

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Date:   Tue, 12 Oct 2021 09:48:52 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Heiko Carstens <hca@...ux.ibm.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] s390: DYNAMIC_FTRACE_WITH_DIRECT_CALL support

On Tue, 12 Oct 2021 15:37:58 +0200
Heiko Carstens <hca@...ux.ibm.com> wrote:

> This small series adds DYNAMIC_FTRACE_WITH_DIRECT_CALL support for
> s390 and is based on linux-next 20211012.

Cool!

> 
> Besides the architecture backend this also adds s390 ftrace direct
> call samples, and slightly changes config option handling a bit, so
> that options only have to be selected. This way also additional future
> architectures can easily add their trampolines to the samples.

Makes sense.

> 
> If ok, I'd like to get this upstream via the s390 tree with the next
> merge window.

A quick look at the patches look fine to me. I'll do a bit more digging
before adding a Reviewed-by.

One thing you may want to note, we are working on fixing direct trampolines
that conflict with the function graph tracer, and have patches that fix it.
I'm not that familiar on how ftrace works on s390, but you may want to
investigate this, because if s390 has the issues that x86 has, where you
can't have both function graph tracing and a direct trampoline on the same
function.

See here:

  https://lore.kernel.org/all/20211008091336.33616-1-jolsa@kernel.org/

-- Steve


> 
> Heiko Carstens (4):
>   s390/ftrace: add HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALL support
>   s390: make STACK_FRAME_OVERHEAD available via asm-offsets.h
>   samples: add HAVE_SAMPLE_FTRACE_DIRECT config option
>   samples: add s390 support for ftrace direct call samples
> 
>  arch/s390/Kconfig                     |  2 ++
>  arch/s390/include/asm/ftrace.h        | 12 ++++++++
>  arch/s390/kernel/asm-offsets.c        |  1 +
>  arch/s390/kernel/mcount.S             | 23 ++++++++++----
>  arch/x86/Kconfig                      |  1 +
>  samples/Kconfig                       |  5 ++-
>  samples/ftrace/ftrace-direct-modify.c | 44 +++++++++++++++++++++++++++
>  samples/ftrace/ftrace-direct-too.c    | 28 +++++++++++++++++
>  samples/ftrace/ftrace-direct.c        | 28 +++++++++++++++++
>  9 files changed, 137 insertions(+), 7 deletions(-)
>