linux-kernel - Re: [PATCH 3/6] x86/dumpstack: make printk_stack

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Message-ID: <CA+55aFzAqoxqzN3eG96qAAMF-qsHe=MWOqi1wK+7Vpq9=-Un1Q@mail.gmail.com>
Date:   Wed, 24 Aug 2016 14:37:21 -0400
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Brian Gerst <brgerst@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Byungchul Park <byungchul.park@....com>,
        Nilay Vaish <nilayvaish@...il.com>
Subject: Re: [PATCH 3/6] x86/dumpstack: make printk_stack_address() more
 generally useful

On Wed, Aug 24, 2016 at 2:22 PM, Peter Zijlstra <peterz@...radead.org> wrote:
>
> I actively disable KASLR on my dev box and feed these hex numbers into
> addr2line -ie vmlinux to find where in the function we are.
>
> Having the option to make %pB generate them works for me.

Yeah, considering that this is the only place this is used, changing
%pB sounds quite reasonable.

We could perhaps make %pB show the hex numbers and address (so pB
would expand to "[<hex>] symbolname".if

 (a) not randomizing (so the hex numbers _may_ be useful)

 (b) kptr_restrict is 0 (so the hex numbers are "safe" in the dmesg)

and fall back to just the symbolic name if either of those aren't true?

And obviously, if KALLSYMS isn't enabled, you always show hex
numbers.. That's already the case (but we might want to add the "[<>}'
markers around the hex numbers just to make the user space automation
we do have work).

            Linus