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

Nicolas Schier
2025-10-11T08:30:14Z

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@redhat.com>
> Closes: https://lore.kernel.org/20251007011637.2512413-1-cmirabil@redhat.com/
> Suggested-by: Alexey Gladkov <legion@kernel.org>
> Signed-off-by: Nathan Chancellor <nathan@kernel.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@kernel.org>