Date:   Mon, 13 Mar 2023 22:48:53 +0100
From:   Michal =?iso-8859-1?Q?Such=E1nek?= <msuchanek@suse.de>
To:     Andrea Righi <andrea.righi@canonical.com>
Cc:     Gary Guo <gary@garyguo.net>, Kees Cook <keescook@chromium.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        linux-kbuild@vger.kernel.org,
        Wedson Almeida Filho <wedsonaf@google.com>,
        Joel Stanley <joel@jms.id.au>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Miguel Ojeda <ojeda@kernel.org>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Nicolas Schier <nicolas@fjasle.eu>,
        rust-for-linux@vger.kernel.org,
        Guo Zhengkui <guozhengkui@vivo.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        Nicholas Piggin <npiggin@gmail.com>,
        =?iso-8859-1?Q?Bj=F6rn?= Roy Baron <bjorn3_gh@protonmail.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        linux-kernel@vger.kernel.org, Julia Lawall <Julia.Lawall@inria.fr>,
        Luis Chamberlain <mcgrof@kernel.org>,
        linuxppc-dev@lists.ozlabs.org, linux-modules@vger.kernel.org
Subject: Re: [PATCH] modpost: support arbitrary symbol length in modversion
Message-ID: <20230313214853.GY19419@kitsune.suse.cz>
References: <20230111161155.1349375-1-gary@garyguo.net>
 <ZA+IUIOAgrWH2oZ0@righiandr-XPS-13-7390>
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Hello,

On Mon, Mar 13, 2023 at 09:32:16PM +0100, Andrea Righi wrote:
> 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@garyguo.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).

Are you using the ELF ABI v1 or v2?

v1 may have some additional issues when it comes to these symbol tables.

Thanks

Michal