linux-kernel - Re: [PATCH v8 0/8] Add generated modalias to modules.builtin.modinfo

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Message-ID: <20250918173529.GA3360630@ax162>
Date: Thu, 18 Sep 2025 10:35:29 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Alexey Gladkov <legion@...nel.org>
Cc: Nicolas Schier <nicolas.schier@...ux.dev>,
	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
Subject: Re: [PATCH v8 0/8] Add generated modalias to modules.builtin.modinfo

Hi Alexey,

On Thu, Sep 18, 2025 at 10:05:44AM +0200, Alexey Gladkov wrote:
> The modules.builtin.modinfo file is used by userspace (kmod to be specific) to
> get information about builtin modules. Among other information about the module,
> information about module aliases is stored. This is very important to determine
> that a particular modalias will be handled by a module that is inside the
> kernel.
> 
> There are several mechanisms for creating modalias for modules:
> 
> The first is to explicitly specify the MODULE_ALIAS of the macro. In this case,
> the aliases go into the '.modinfo' section of the module if it is compiled
> separately or into vmlinux.o if it is builtin into the kernel.
> 
> The second is the use of MODULE_DEVICE_TABLE followed by the use of the
> modpost utility. In this case, vmlinux.o no longer has this information and
> does not get it into modules.builtin.modinfo.
> 
> For example:
> 
> $ modinfo pci:v00008086d0000A36Dsv00001043sd00008694bc0Csc03i30
> modinfo: ERROR: Module pci:v00008086d0000A36Dsv00001043sd00008694bc0Csc03i30 not found.
> 
> $ modinfo xhci_pci
> name:           xhci_pci
> filename:       (builtin)
> license:        GPL
> file:           drivers/usb/host/xhci-pci
> description:    xHCI PCI Host Controller Driver
> 
> The builtin module is missing alias "pci:v*d*sv*sd*bc0Csc03i30*" which will be
> generated by modpost if the module is built separately.
> 
> To fix this it is necessary to add the generated by modpost modalias to
> modules.builtin.modinfo. Fortunately modpost already generates .vmlinux.export.c
> for exported symbols. It is possible to add `.modinfo` for builtin modules and
> modify the build system so that `.modinfo` section is extracted from the
> intermediate vmlinux after modpost is executed.

This seems good to me now. I have tentatively merged this into
kbuild-next so that it can get some more soak testing in -next, as I am
going to be paying less attention to email starting on Sunday for a week
or so, so I would like to be able to deal with regressions promptly.

  https://git.kernel.org/kbuild/l/kbuild-next

Don't consider the commit hashes stable just yet, as I would like to
give Nicolas the chance to provide tags if he would like but I did not
want to wait for the soak testing.

Cheers,
Nathan