linux-kernel - Re: [PATCH 02/17] kallsyms: increase maximum kernel symbol length to 512

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Message-ID: <CAHk-=whdi_biEOrzrYn7OC+wq+ckoaa5dFAATdM=n9P7Dp0YOA@mail.gmail.com>
Date:   Wed, 14 Jul 2021 13:21:57 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        rust-for-linux <rust-for-linux@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Geoffrey Thomas <geofft@...reload.com>,
        Finn Behrens <me@...enk.de>,
        Adam Bratschi-Kaye <ark.email@...il.com>,
        Wedson Almeida Filho <wedsonaf@...gle.com>
Subject: Re: [PATCH 02/17] kallsyms: increase maximum kernel symbol length to 512

On Wed, Jul 14, 2021 at 1:09 PM Eric W. Biederman <ebiederm@...ssion.com> wrote:
>
> Are you thinking the hashed kernel symbols need to have their types
> included in the hash?

I think the hash should be the whole mangled name. So yes, for Rust
symbols they'd have the the type information.

>  Or is this just a hash to make the names a managable size?

No, if that was the only point of it, the "just use two bytes for
length" would be simpler.

But I don't think we want to do run-time de-mangling of names in the
kernel when doing stack traces, which implies that the kallsym
information in the kernel should be the de-mangled names.

That makes the names nice and readable, and also makes this "maximum
symbol length" thing a non-issue.

BUT.

It also means that you can't use those names for linking purposes, so
you'd then need to have a "full version" for that. But as Willy
pointed out elsewhere, you might as well just use a constant-sized
hash for that, rather than have both a manged and a de-mangled name.

                   Linus