linux-kernel - Re: [PATCH 01/13] kallsyms: Support "big" kernel symbols (2-byte lengths)

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Message-ID: <CANiq72k1w8__rCAZs1NbVvB=gXp_AX9=H-KYbdoLCcmYFEWc_w@mail.gmail.com>
Date:   Wed, 14 Apr 2021 21:59:24 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        rust-for-linux@...r.kernel.org,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        linux-kernel <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 01/13] kallsyms: Support "big" kernel symbols (2-byte lengths)

On Wed, Apr 14, 2021 at 9:45 PM Matthew Wilcox <willy@...radead.org> wrote:
>
> How about doing something a bit more utf-8-like?
>
>         len = data[0];
>         if (len == 0)
>                 error
>         else if (len < 128)
>                 return len;
>         else if (len < 192)
>                 return 128 + (len - 128) * 256 + data[1];
> ... that takes you all the way out to 16511 bytes.  You probably don't

That would save some space and allow us to keep the 0 as an error, yeah.

> Alternatively, if the symbols are really this long, perhaps we should not
> do string matches.  A sha-1 (... or whatever ...) hash of the function
> name is 160 bits.  Expressed as hex digits, that's 40 characters.
> Expressed in base-64, it's 27 characters.  We'd also want a "pretty"
> name to go along with the hash, but that seems preferable to printing
> out a mangled-with-types-and-who-knows-what name.

I have seen symbols up to ~300, but I don't think we will ever go up
to more than, say, 1024, unless we start to go crazy with generics,
namespaces and what not.

Hashing could be a nice solution if they really grow, yeah.

> If you have C-d-b, you don't also need S-o-b.

Hmm... `submitting-patches.rst` keeps the S-o-b in the example they
give, is it outdated?

Cheers,
Miguel