linux-kernel - Re: [PATCH] kbuild: Use '--strip-unneeded-symbol' for removing module device table symbols

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Message-ID: <aOoRhgzntzk2YKYP@levanger>
Date: Sat, 11 Oct 2025 10:12:54 +0200
From: Nicolas Schier <nsc@...nel.org>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Alexey Gladkov <legion@...nel.org>,
	Masahiro Yamada <masahiroy@...nel.org>,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Alexander Potapenko <glider@...gle.com>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com,
	Charles Mirabile <cmirabil@...hat.com>
Subject: Re: [PATCH] kbuild: Use '--strip-unneeded-symbol' for removing
 module device table symbols

On Fri, Oct 10, 2025 at 02:49:27PM -0700, Nathan Chancellor wrote:
> After commit 5ab23c7923a1 ("modpost: Create modalias for builtin
> modules"), relocatable RISC-V kernels with CONFIG_KASAN=y start failing
> when attempting to strip the module device table symbols:
> 
>   riscv64-linux-objcopy: not stripping symbol `__mod_device_table__kmod_irq_starfive_jh8100_intc__of__starfive_intc_irqchip_match_table' because it is named in a relocation
>   make[4]: *** [scripts/Makefile.vmlinux:97: vmlinux] Error 1
> 
> The relocation appears to come from .LASANLOC5 in .data.rel.local:
> 
>   $ llvm-objdump --disassemble-symbols=.LASANLOC5 --disassemble-all -r drivers/irqchip/irq-starfive-jh8100-intc.o
> 
>   drivers/irqchip/irq-starfive-jh8100-intc.o:   file format elf64-littleriscv
> 
>   Disassembly of section .data.rel.local:
> 
>   0000000000000180 <.LASANLOC5>:
>   ...
>        1d0: 0000          unimp
>                   00000000000001d0:  R_RISCV_64   __mod_device_table__kmod_irq_starfive_jh8100_intc__of__starfive_intc_irqchip_match_table
>   ...
> 
> This section appears to come from GCC for including additional
> information about global variables that may be protected by KASAN.
> 
> There appears to be no way to opt out of the generation of these symbols
> through either a flag or attribute. Attempting to remove '.LASANLOC*'
> with '--strip-symbol' results in the same error as above because these
> symbols may refer to (thus have relocation between) each other.
> 
> Avoid this build breakage by switching to '--strip-unneeded-symbol' for
> removing __mod_device_table__ symbols, as it will only remove the symbol
> when there is no relocation pointing to it. While this may result in a
> little more bloat in the symbol table in certain configurations, it is
> not as bad as outright build failures.
> 
> Fixes: 5ab23c7923a1 ("modpost: Create modalias for builtin modules")
> Reported-by: Charles Mirabile <cmirabil@...hat.com>
> Closes: https://lore.kernel.org/20251007011637.2512413-1-cmirabil@redhat.com/
> Suggested-by: Alexey Gladkov <legion@...nel.org>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
> I am Cc'ing KASAN folks in case they have any additional knowledge
> around .LASANLOC symbols or how to remove/avoid them.
> 
> I plan to send this to Linus tomorrow.
> ---
>  scripts/Makefile.vmlinux | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 

Thanks!

Tested-by: Nicolas Schier <nsc@...nel.org>