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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Mon, 15 Feb 2021 19:31:49 +0100
Message-ID: <CAMj1kXGEP3BNW6aLDaHFq2FCer-e8VXPU3c8xiojNXSqgzdw_g@mail.gmail.com>
Subject: Re: [PATCH v7 0/2] ARM: Implement MODULE_PLT support in FTRACE
To:     Florian Fainelli <f.fainelli@gmail.com>,
        Linus Walleij <linus.walleij@linaro.org>
Cc:     Alexander A Sverdlin <alexander.sverdlin@nokia.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Russell King <linux@armlinux.org.uk>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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(+ Linus)

On Wed, 3 Feb 2021 at 19:24, Florian Fainelli <f.fainelli@gmail.com> wrote:
>
> On 1/27/21 3:09 AM, Alexander A Sverdlin wrote:
> > From: Alexander Sverdlin <alexander.sverdlin@nokia.com>
> >
> > FTRACE's function tracer currently doesn't always work on ARM with
> > MODULE_PLT option enabled. If the module is loaded too far, FTRACE's
> > code modifier cannot cope with introduced veneers and turns the
> > function tracer off globally.
> >
> > ARM64 already has a solution for the problem, refer to the following
> > patches:
> >
> > arm64: ftrace: emit ftrace-mod.o contents through code
> > arm64: module-plts: factor out PLT generation code for ftrace
> > arm64: ftrace: fix !CONFIG_ARM64_MODULE_PLTS kernels
> > arm64: ftrace: fix building without CONFIG_MODULES
> > arm64: ftrace: add support for far branches to dynamic ftrace
> > arm64: ftrace: don't validate branch via PLT in ftrace_make_nop()
> >
> > But the presented ARM variant has just a half of the footprint in terms of
> > the changed LoCs. It also retains the code validation-before-modification
> > instead of switching it off.
>
> Ard, Russell should this be sent to the patch tracker?

Apologies for the delay. Unfortunately, I don't have time to review this.

Linus?