linux-kernel - Re: [PATCH v8 7/8] modpost: Create modalias for builtin modules

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Message-ID: <aOgSaNejdcBWKXx8@levanger>
Date: Thu, 9 Oct 2025 21:52:08 +0200
From: Nicolas Schier <nsc@...nel.org>
To: Alexey Gladkov <legion@...nel.org>
Cc: Charles Mirabile <cmirabil@...hat.com>, da.gomez@...sung.com,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-modules@...r.kernel.org, masahiroy@...nel.org,
	mcgrof@...nel.org, nathan@...nel.org, petr.pavlu@...e.com,
	samitolvanen@...gle.com, sfr@...b.auug.org.au
Subject: Re: [PATCH v8 7/8] modpost: Create modalias for builtin modules

On Tue, Oct 07, 2025 at 12:15:21PM +0200, Alexey Gladkov wrote:
> On Mon, Oct 06, 2025 at 09:16:37PM -0400, Charles Mirabile wrote:
> > On Thu, Sep 18, 2025 at 10:05:51AM +0200, Alexey Gladkov wrote:
> > > For some modules, modalias is generated using the modpost utility and
> > > the section is added to the module file.
> > > 
> > > When a module is added inside vmlinux, modpost does not generate
> > > modalias for such modules and the information is lost.
> > > 
> > > As a result kmod (which uses modules.builtin.modinfo in userspace)
> > > cannot determine that modalias is handled by a builtin kernel module.
> > > 
> > > $ cat /sys/devices/pci0000:00/0000:00:14.0/modalias
> > > pci:v00008086d0000A36Dsv00001043sd00008694bc0Csc03i30
> > > 
> > > $ modinfo xhci_pci
> > > name:           xhci_pci
> > > filename:       (builtin)
> > > license:        GPL
> > > file:           drivers/usb/host/xhci-pci
> > > description:    xHCI PCI Host Controller Driver
> > > 
> > > Missing modalias "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 generate the same modalias for vmlinux as
> > > for the individual modules. Fortunately '.vmlinux.export.o' is already
> > > generated from which '.modinfo' can be extracted in the same way as for
> > > vmlinux.o.
> > 
> > Hi -
> > 
> > This patch broke RISC-V builds for me. During the final objcopy where the new
> > symbols are supposed to be stripped, an error occurs producing lots of error
> > messages similar to this one:
> > 
> > riscv64-linux-gnu-objcopy: not stripping symbol `__mod_device_table__...'
> > because it is named in a relocation
> > 
> > It does not occur using defconfig, but I was able to bisect my way to this
> > commit and then reduce my config delta w.r.t defconfig until I landed on:
> > 
> > cat > .config <<'EOF'
> > CONFIG_RELOCATABLE=y
> > CONFIG_KASAN=y
> > EOF
> > ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu- make olddefconfig
> > ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu- make -j $(nproc)
> > ...
> >   LD      vmlinux.unstripped
> >   NM      System.map
> >   SORTTAB vmlinux.unstripped
> >   CHKREL  vmlinux.unstripped
> >   OBJCOPY vmlinux
> >   OBJCOPY modules.builtin.modinfo
> >   GEN     modules.builtin
> > riscv64-linux-gnu-objcopy: not stripping symbol `<long symbol name>'
> > because it is named in a relocation
> > <repeats with different symbol names about a dozen times>
> > make[3]: *** [scripts/Makefile.vmlinux:97: vmlinux] Error 1
> > make[3]: *** Deleting file 'vmlinux'
> > make[2]: *** [Makefile:1242: vmlinux] Error 2
> > make[1]: *** [/tmp/linux/Makefile:369: __build_one_by_one] Error 2
> > make: *** [Makefile:248: __sub-make] Error 2
> > 
> > I confirmed that reverting this commit fixes the issue.

Thanks for the report!

> 
> Hm. Indeed. I haven't found a good solution yet, but you can use the
> following patch to unlock compilation. It won't solve the problem, it will
> only hide it.
> 
> --- a/scripts/Makefile.vmlinux
> +++ b/scripts/Makefile.vmlinux
> @@ -84,7 +84,7 @@ endif
>  remove-section-y                                   := .modinfo
>  remove-section-$(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS) += '.rel*'
> 
> -remove-symbols := -w --strip-symbol='__mod_device_table__*'
> +remove-symbols := -w --strip-unneeded-symbol='__mod_device_table__*'
> 
>  # To avoid warnings: "empty loadable segment detected at ..." from GNU objcopy,
>  # it is necessary to remove the PT_LOAD flag from the segment.
> 

Is it problematic to hide that?  Otherwise we'd have to revert the
patch, right?

Kind regards,
Nicolas