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From: Matthew Wilcox <willy@infradead.org>
To: Gary Guo <gary@garyguo.net>
Cc: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
	Miguel Ojeda <ojeda@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.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>,
	Linux Doc Mailing List <linux-doc@vger.kernel.org>,
	linux-kernel <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>
Subject: Re: [PATCH 01/17] kallsyms: support big kernel symbols (2-byte lengths)
Date: Sun, 4 Jul 2021 23:42:03 +0100	[thread overview]
Message-ID: <YOI5O6/RpaN1P6mM@casper.infradead.org> (raw)
In-Reply-To: <20210704232007.0000357e@garyguo.net>

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;
                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.  If you want to make an argument about extensibiity, then
I'm going to suggest that wanting a symbol name more than 32kB in size
is a sign you've done something else very, very wrong.

At that point, you should probably switch to comparing hashes of the
symbol instead of the symbol.  Indeed, I think we're already there at
300 byte symbols; we should probably SipHash the full, unmangled symbol
[1].  At 33k symbols in the current kernel, the risk of a collision of
a 64-bit value is negligible, and almost every kernel symbol is longer
than 7 bytes (thankfully).

[1] ie SipHash("void unlock_page(struct page *)")

  reply	other threads:[~2021-07-04 22:42 UTC|newest]

Thread overview: 73+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-04 20:27 [PATCH 00/17] Rust support ojeda
2021-07-04 20:27 ` [PATCH 01/17] kallsyms: support big kernel symbols (2-byte lengths) ojeda
2021-07-04 20:52   ` Linus Torvalds
2021-07-04 21:15     ` Miguel Ojeda
2021-07-04 21:28       ` Linus Torvalds
2021-07-04 21:04   ` Matthew Wilcox
2021-07-04 21:17     ` Miguel Ojeda
2021-07-04 21:33       ` Matthew Wilcox
2021-07-04 21:49         ` Matthew Wilcox
2021-07-04 22:07           ` Miguel Ojeda
2021-07-04 22:20         ` Gary Guo
2021-07-04 22:42           ` Matthew Wilcox [this message]
2021-07-04 23:14             ` Gary Guo
2021-07-13 18:02             ` Kent Overstreet
2021-07-04 21:20     ` Gary Guo
2021-07-05  4:35       ` Willy Tarreau
2021-07-04 20:27 ` [PATCH 02/17] kallsyms: increase maximum kernel symbol length to 512 ojeda
2021-07-14 18:20   ` Nick Desaulniers
2021-07-14 19:04     ` Linus Torvalds
2021-07-14 20:09       ` Eric W. Biederman
2021-07-14 20:21         ` Linus Torvalds
2021-07-14 20:48           ` Eric W. Biederman
2021-07-14 22:40             ` Linus Torvalds
2021-07-14 20:19     ` Miguel Ojeda
2021-07-04 20:27 ` [PATCH 03/17] Makefile: generate `CLANG_FLAGS` even in GCC builds ojeda
2021-07-14 18:13   ` Nick Desaulniers
2021-07-14 18:16     ` Nick Desaulniers
2021-07-14 20:31     ` Miguel Ojeda
2021-07-04 20:27 ` [PATCH 04/17] vsprintf: add new `%pA` format specifier ojeda
2021-07-07 20:31   ` Nick Desaulniers
2021-07-07 22:33     ` Miguel Ojeda
2021-07-04 20:27 ` [PATCH 05/17] rust: add C helpers ojeda
2021-07-07 10:19   ` Marco Elver
2021-07-09 10:31     ` Marco Elver
2021-07-09 14:32     ` Miguel Ojeda
2021-07-04 20:27 ` [PATCH 06/17] rust: add `compiler_builtins` crate ojeda
2021-07-04 20:27 ` [PATCH 07/17] rust: add `alloc` crate ojeda
2021-07-04 20:27 ` [PATCH 08/17] rust: add `build_error` crate ojeda
2021-07-04 20:27 ` [PATCH 09/17] rust: add `macros` crate ojeda
2021-07-04 20:27 ` [PATCH 10/17] rust: add `kernel` crate ojeda
2021-07-04 20:27 ` [PATCH 11/17] rust: export generated symbols ojeda
2021-07-04 20:27 ` [PATCH 12/17] Kbuild: add Rust support ojeda
2021-07-04 20:27 ` [PATCH 13/17] docs: add Rust documentation ojeda
2021-07-05  5:02   ` Willy Tarreau
2021-07-06  0:06     ` Miguel Ojeda
2021-07-06  2:09       ` Willy Tarreau
2021-07-14 18:37   ` Nick Desaulniers
2021-07-14 19:55     ` Miguel Ojeda
2021-07-04 20:27 ` [PATCH 14/17] samples: add Rust examples ojeda
2021-07-04 20:27 ` [PATCH 15/17] scripts: add `generate_rust_analyzer.py` ojeda
2021-07-05  5:05   ` Willy Tarreau
2021-07-05 23:41     ` Miguel Ojeda
2021-07-04 20:27 ` [PATCH 16/17] MAINTAINERS: Rust ojeda
2021-07-06  0:26   ` Pedro Tammela
2021-07-06 22:14     ` Miguel Ojeda
2021-07-04 20:27 ` [RFC PATCH 17/17] Android: Binder IPC in Rust (WIP) ojeda
2021-07-04 23:11 ` [PATCH 00/17] Rust support Miguel Ojeda
2021-07-07  6:43 ` Christoph Hellwig
2021-07-07 12:33   ` Miguel Ojeda
2021-07-07 12:50     ` Greg Kroah-Hartman
2021-07-07 14:07       ` Wedson Almeida Filho
2021-07-07 14:12         ` Christoph Hellwig
2021-07-07 15:02         ` Greg Kroah-Hartman
2021-07-07 20:56           ` Finn Behrens
2021-07-08  0:58             ` Matthew Wilcox
2021-07-08  6:39               ` [PATCH 00/17] Rust support, NVMe Geert Stappers
2021-07-08  8:29                 ` Finn Behrens
2021-07-22 22:55               ` [PATCH 00/17] Rust support Wedson Almeida Filho
2021-07-23  1:17                 ` Matthew Wilcox
2021-07-23 11:33                   ` [PATCH 00/17] Rust support, GPIO driver Geert Stappers
2021-07-23 15:08                 ` [PATCH 00/17] Rust support Keith Busch
2021-07-07 10:51 ` Marco Elver
2021-07-07 11:28   ` Miguel Ojeda

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