linux-kernel - Re: [PATCH 01/17] kallsyms: support big kernel symbols (2-byte lengths)

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Message-ID: <20210705001417.00003d1f@garyguo.net>
Date:   Mon, 5 Jul 2021 00:14:17 +0100
From:   Gary Guo <gary@...yguo.net>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.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>,
        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 01/17] kallsyms: support big kernel symbols (2-byte
 lengths)

On Sun, 4 Jul 2021 23:42:03 +0100
Matthew Wilcox <willy@...radead.org> wrote:

> On Sun, Jul 04, 2021 at 11:20:07PM +0100, Gary Guo wrote:
> > This is big endian.  
> 
> Fundamentally, it doesn't matter whether it's encoded as top-7 +
> bottom-8 or bottom-7 + top-8.  It could just as well be:
> 
>         if (len >= 128) {
>                 len -= 128;
>                 len += *data * 256;

Do you mean `*data * 128`?

>                 data++;
>         }
> 
> It doesn't matter whether it's compatible with some other encoding.
> This encoding has one producer and one consumer.  As long as they
> agree, it's fine.

I am aware that this is only for internal tooling so it doesn't
really matter. I mentioned that it's big endian to do top-7 +
bottom-8 because Linus suggests that big-endian shouldn't be
used.