linux-kernel - Re: [PATCH] modpost: support arbitrary symbol length in modversion

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Message-ID: <ZA+IUIOAgrWH2oZ0@righiandr-XPS-13-7390>
Date:   Mon, 13 Mar 2023 21:32:16 +0100
From:   Andrea Righi <andrea.righi@...onical.com>
To:     Gary Guo <gary@...yguo.net>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Kees Cook <keescook@...omium.org>,
        Joel Stanley <joel@....id.au>,
        Julia Lawall <Julia.Lawall@...ia.fr>,
        Guo Zhengkui <guozhengkui@...o.com>,
        Wedson Almeida Filho <wedsonaf@...gle.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-modules@...r.kernel.org, linux-kbuild@...r.kernel.org,
        rust-for-linux@...r.kernel.org
Subject: Re: [PATCH] modpost: support arbitrary symbol length in modversion

On Wed, Jan 11, 2023 at 04:11:51PM +0000, Gary Guo wrote:
> Currently modversion uses a fixed size array of size (64 - sizeof(long))
> to store symbol names, thus placing a hard limit on length of symbols.
> Rust symbols (which encodes crate and module names) can be quite a bit
> longer. The length limit in kallsyms is increased to 512 for this reason.
> 
> It's a waste of space to simply expand the fixed array size to 512 in
> modversion info entries. I therefore make it variably sized, with offset
> to the next entry indicated by the initial "next" field.
> 
> In addition to supporting longer-than-56/60 byte symbols, this patch also
> reduce the size for short symbols by getting rid of excessive 0 paddings.
> There are still some zero paddings to ensure "next" and "crc" fields are
> properly aligned.
> 
> This patch does have a tiny drawback that it makes ".mod.c" files generated
> a bit less easy to read, as code like
> 
> 	"\x08\x00\x00\x00\x78\x56\x34\x12"
> 	"symbol\0\0"
> 
> is generated as opposed to
> 
> 	{ 0x12345678, "symbol" },
> 
> because the structure is now variable-length. But hopefully nobody reads
> the generated file :)
> 
> Link: b8a94bfb3395 ("kallsyms: increase maximum kernel symbol length to 512")
> Link: https://github.com/Rust-for-Linux/linux/pull/379
> 
> Signed-off-by: Gary Guo <gary@...yguo.net>

Is there any newer version of this patch?

I'm doing some tests with it, but I'm getting boot failures on ppc64
with this applied (at boot kernel is spitting out lots of oops'es and
unfortunately it's really hard to copy paste or just read them from the
console).

Thanks,
-Andrea