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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Tue, 29 Oct 2019 13:35:40 -0700
Message-ID: <CAKwvOdkxrYB=HTmtQ6sejPmWZh-mwJ-gyWRGgtZDrUOjBMftzg@mail.gmail.com>
Subject: Re: [PATCH v2 09/17] arm64: disable function graph tracing with SCS
To:     Mark Rutland <mark.rutland@arm.com>,
        Kristof Beyls <Kristof.Beyls@arm.com>
Cc:     Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Dave Martin <Dave.Martin@arm.com>,
        Kees Cook <keescook@chromium.org>,
        Laura Abbott <labbott@redhat.com>,
        Jann Horn <jannh@google.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Sami Tolvanen <samitolvanen@google.com>
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On Tue, Oct 29, 2019 at 10:45 AM Sami Tolvanen <samitolvanen@google.com> wrote:
>
> On Fri, Oct 25, 2019 at 4:03 AM Mark Rutland <mark.rutland@arm.com> wrote:
> > We have a similar issue with pointer authentication, and we're solving
> > that with -fpatchable-function-entry, which allows us to hook the
> > callsite before it does anything with the return address. IIUC we could
> > use the same mechanism here (and avoid introducing a third).
> >
> > Are there plans to implement -fpatchable-function-entry on the clang
> > side?
>
> I'm not sure if there are plans at the moment, but if this feature is
> needed for PAC, adding it to clang shouldn't be a problem. Nick, did
> you have any thoughts on this?

I didn't see anything explicitly in LLVM's issue tracker.  I also
didn't see -fpatchable-function-entry currently in -next other than
under arch/parisc.  Are there patches I can look at?

Has ARM's kernel team expressed the need to ARM's LLVM team?
-- 
Thanks,
~Nick Desaulniers