linux-kernel - Re: [PATCH v10 4/5] Documentation/kbuild: Document storage of symbol information

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Message-ID: <e522ec59-6ee6-4c11-8a4f-91a683e6435c@suse.com>
Date: Mon, 16 Dec 2024 14:25:33 +0100
From: Petr Pavlu <petr.pavlu@...e.com>
To: Matthew Maurer <mmaurer@...gle.com>
Cc: Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin
 <npiggin@...il.com>, Christophe Leroy <christophe.leroy@...roup.eu>,
 Naveen N Rao <naveen@...nel.org>, Madhavan Srinivasan <maddy@...ux.ibm.com>,
 Luis Chamberlain <mcgrof@...nel.org>, Petr Pavlu <petr.pavlu@...e.com>,
 Sami Tolvanen <samitolvanen@...gle.com>, Daniel Gomez
 <da.gomez@...sung.com>, Masahiro Yamada <masahiroy@...nel.org>,
 Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>,
 Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
 Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Benno Lossin <benno.lossin@...ton.me>,
 Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>, Jonathan Corbet <corbet@....net>,
 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, linux-doc@...r.kernel.org
Subject: Re: [PATCH v10 4/5] Documentation/kbuild: Document storage of symbol
 information

On 11/23/24 03:42, Matthew Maurer wrote:
> Document where exported and imported symbols are kept, format options,
> and limitations.
> 
> Signed-off-by: Matthew Maurer <mmaurer@...gle.com>
> ---
>  Documentation/kbuild/modules.rst | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/Documentation/kbuild/modules.rst b/Documentation/kbuild/modules.rst
> index 101de236cd0c9abe1f5684d80063ff3f9a7fc673..c32e3ed67cd26070f6929f6ad98c4308a1ab71f8 100644
> --- a/Documentation/kbuild/modules.rst
> +++ b/Documentation/kbuild/modules.rst
> @@ -423,6 +423,26 @@ Symbols From the Kernel (vmlinux + modules)
>  	1) It lists all exported symbols from vmlinux and all modules.
>  	2) It lists the CRC if CONFIG_MODVERSIONS is enabled.
>  
> +Version Information Formats
> +---------------------------
> +
> +	Exported symbols have information stored in __ksymtab or __ksymtab_gpl
> +	sections. Symbol names and namespaces are stored in __kstrtab and
> +	__kstrtabns respectively, using a format similar to the string table
> +	used for ELF. If CONFIG_MODVERSIONS is enabled, the CRCs corresponding
> +	to exported symbols will be added to the __kcrctab or __kcrctab_gpl.

The second sentence should be that symbol names and namespaces of
exported symbols are both stored in the __ksymtab_strings section.

> +
> +	If CONFIG_BASIC_MODVERSIONS is enabled (default with
> +	CONFIG_MODVERSIONS), imported symbols will have their symbol name and
> +	CRC stored in the __versions section of the importing module. This
> +	mode only supports symbols of length up to 64 bytes.
> +
> +	If CONFIG_EXTENDED_MODVERSIONS is enabled (required to enable both
> +	CONFIG_MODVERSIONS and CONFIG_RUST at the same time), imported symbols
> +	will have their symbol name recorded in the __version_ext_names
> +	section as a series of concatenated, null-terminated strings. CRCs for
> +	these symbols will be recorded in the __version_ext_crcs section.
> +
>  Symbols and External Modules
>  ----------------------------
>  
> 

-- 
Thanks,
Petr