linux-kernel - Re: [PATCH v6 6/9] modpost: Add modname to mod_device

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Message-Id: <DC27G409IQGT.H9G83QDQ9V7R@kernel.org>
Date: Thu, 14 Aug 2025 16:03:01 +0200
From: "Danilo Krummrich" <dakr@...nel.org>
To: "Alexey Gladkov" <legion@...nel.org>
Cc: "Nathan Chancellor" <nathan@...nel.org>, "Nicolas Schier"
 <nicolas.schier@...ux.dev>, "Masahiro Yamada" <masahiroy@...nel.org>, "Petr
 Pavlu" <petr.pavlu@...e.com>, "Luis Chamberlain" <mcgrof@...nel.org>, "Sami
 Tolvanen" <samitolvanen@...gle.com>, "Daniel Gomez" <da.gomez@...sung.com>,
 <linux-kernel@...r.kernel.org>, <linux-modules@...r.kernel.org>,
 <linux-kbuild@...r.kernel.org>, "Miguel Ojeda" <ojeda@...nel.org>, "Andreas
 Hindborg" <a.hindborg@...nel.org>, "Alex Gaynor" <alex.gaynor@...il.com>,
 <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH v6 6/9] modpost: Add modname to mod_device_table alias

On Thu Aug 14, 2025 at 3:54 PM CEST, Alexey Gladkov wrote:
> On Thu, Aug 14, 2025 at 03:26:53PM +0200, Danilo Krummrich wrote:
>> On Thu Aug 14, 2025 at 3:07 PM CEST, Alexey Gladkov wrote:
>> > At this point, if a symbol is compiled as part of the kernel,
>> > information about which module the symbol belongs to is lost.
>> >
>> > To save this it is possible to add the module name to the alias name.
>> > It's not very pretty, but it's possible for now.
>> >
>> > Cc: Miguel Ojeda <ojeda@...nel.org>
>> > Cc: Andreas Hindborg <a.hindborg@...nel.org>
>> > Cc: Danilo Krummrich <dakr@...nel.org>
>> > Cc: Alex Gaynor <alex.gaynor@...il.com>
>> > Cc: rust-for-linux@...r.kernel.org
>> > Signed-off-by: Alexey Gladkov <legion@...nel.org>
>> > ---
>> >  include/linux/module.h   | 14 +++++++++++++-
>> >  rust/kernel/device_id.rs |  8 ++++----
>> >  scripts/mod/file2alias.c | 18 ++++++++++++++----
>> >  3 files changed, 31 insertions(+), 9 deletions(-)
>> >
>> > diff --git a/include/linux/module.h b/include/linux/module.h
>> > index 3319a5269d28..e31ee29fac6b 100644
>> > --- a/include/linux/module.h
>> > +++ b/include/linux/module.h
>> > @@ -244,10 +244,22 @@ struct module_kobject *lookup_or_create_module_kobject(const char *name);
>> >  /* What your module does. */
>> >  #define MODULE_DESCRIPTION(_description) MODULE_INFO(description, _description)
>> >  
>> > +/*
>> > + * Format: __mod_device_table__kmod_<modname>__<type>__<name>
>> > + * Parts of the string `__kmod_` and `__` are used as delimiters when parsing
>> > + * a symbol in file2alias.c
>> > + */
>> > +#define __mod_device_table(type, name)	\
>> > +	__PASTE(__mod_device_table__,	\
>> > +	__PASTE(__KBUILD_MODNAME,	\
>> > +	__PASTE(__,			\
>> > +	__PASTE(type,			\
>> > +	__PASTE(__, name)))))
>> > +
>> >  #ifdef MODULE
>> >  /* Creates an alias so file2alias.c can find device table. */
>> >  #define MODULE_DEVICE_TABLE(type, name)					\
>> > -static typeof(name) __mod_device_table__##type##__##name		\
>> > +static typeof(name) __mod_device_table(type, name)			\
>> >    __attribute__ ((used, alias(__stringify(name))))
>> >  #else  /* !MODULE */
>> >  #define MODULE_DEVICE_TABLE(type, name)
>> > diff --git a/rust/kernel/device_id.rs b/rust/kernel/device_id.rs
>> > index 70d57814ff79..62c42da12e9d 100644
>> > --- a/rust/kernel/device_id.rs
>> > +++ b/rust/kernel/device_id.rs
>> > @@ -195,10 +195,10 @@ macro_rules! module_device_table {
>> >      ($table_type: literal, $module_table_name:ident, $table_name:ident) => {
>> >          #[rustfmt::skip]
>> >          #[export_name =
>> > -            concat!("__mod_device_table__", $table_type,
>> > -                    "__", module_path!(),
>> > -                    "_", line!(),
>> > -                    "_", stringify!($table_name))
>> > +            concat!("__mod_device_table__", line!(),
>> 
>> Why do we have line!() between "__mod_device_table__" and "__kmod_", while the
>> format is defined as "__mod_device_table__kmod_<modname>__<type>__<name>" above?
>
> The "__mod_device_table__" is used to filter symbols.
> The meaning part starts after "__kmod_" part. After that, order becomes
> important.
>
>> The previous logic was to create a unique name with
>> using "<module_path>_<line>_<table_name>" as "<name>". So, I think this should
>> actually be:
>> 
>> 	concat!("__mod_device_table__kmod_",
>> 		module_path!(),
>> 		"__", $table_type,
>> 		"__", stringify!($table_name),
>> 		"_", line!())
>> 
>> rather than the below.
>
> No. "stringify!($table_name)" should be the last thing in this string.
> This is the a symbol name that will be searched for in the elf to generate
> modalias.

$table_name is not guaranteed to be unique for a certain module_path!(), hence
we need line!() to guarantee uniqueness.

The symbol name will be unique no matter where you place line!() of course, but
$table_name + line!() is the unique table name, which I think is what we want?

>> 
>> > +                    "__kmod_", module_path!(),
>> > +                    "__", $table_type,
>> > +                    "__", stringify!($table_name))
>> >          ]
>> >          static $module_table_name: [::core::mem::MaybeUninit<u8>; $table_name.raw_ids().size()] =
>> >              unsafe { ::core::mem::transmute_copy($table_name.raw_ids()) };
>> 
>
> -- 
> Rgrds, legion