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

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Message-ID: <aJ3qsonmvUUErQx9@example.org>
Date: Thu, 14 Aug 2025 15:54:58 +0200
From: Alexey Gladkov <legion@...nel.org>
To: Danilo Krummrich <dakr@...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 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.

> 
> > +                    "__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