linux-kernel - Re: [POC][RFC][PATCH 1/2] jump_function: Addition of new feature "jump

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Message-ID: <CALCETrVHRV6nVANL7i1qGBY3vp9kfY_S1tvnhiL+iowr5RDzxg@mail.gmail.com>
Date:   Mon, 8 Oct 2018 10:47:10 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Jiri Kosina <jikos@...nel.org>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        mhelsley@...are.com,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jason Baron <jbaron@...mai.com>,
        Andrew Lutomirski <luto@...nel.org>
Subject: Re: [POC][RFC][PATCH 1/2] jump_function: Addition of new feature "jump_function"

On Mon, Oct 8, 2018 at 10:44 AM Jiri Kosina <jikos@...nel.org> wrote:
>
> On Mon, 8 Oct 2018, Ard Biesheuvel wrote:
>
> > Does that mean that architectures could opt out of doing the whole
> > objtool + relocation processing thing, and instead take the hit of
> > going through the trampoline for all calls?
>
> There are architectures that aren't [currently] supported by objtool at
> all anyway.
>

The the credit of most architectures, though, the only reason x86
would want to use objtool instead of digging the results directly out
of the relocation data is that x86 has an overcomplicated instruction
encoding and there's no fully reliable way to find the address of the
instruction that contains a given relocation without fully
disassembling the binary.