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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 14 Jul 2021 13:21:57 -0700
Message-ID: <CAHk-=whdi_biEOrzrYn7OC+wq+ckoaa5dFAATdM=n9P7Dp0YOA@mail.gmail.com>
Subject: Re: [PATCH 02/17] kallsyms: increase maximum kernel symbol length to 512
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Nick Desaulniers <ndesaulniers@google.com>,
        Miguel Ojeda <ojeda@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        rust-for-linux <rust-for-linux@vger.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Geoffrey Thomas <geofft@ldpreload.com>,
        Finn Behrens <me@kloenk.de>,
        Adam Bratschi-Kaye <ark.email@gmail.com>,
        Wedson Almeida Filho <wedsonaf@google.com>
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On Wed, Jul 14, 2021 at 1:09 PM Eric W. Biederman <ebiederm@xmission.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