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

[Nathan Chancellor]

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 <cmir...@redhat.com>
Closes: https://lore.kernel.org/20251007011637.2...@redhat.com/
Suggested-by: Alexey Gladkov <leg...@kernel.org>
Signed-off-by: Nathan Chancellor <nat...@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(-)

diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux
index c02f85c2e241..ced4379550d7 100644
--- a/scripts/Makefile.vmlinux
+++ b/scripts/Makefile.vmlinux
@@ -87,7 +87,7 @@ remove-section-$(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS) += '.rel*' '!.rel*.dyn'
# https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=c12d9fa2afe7abcbe407a00e15719e1a1350c2a7
remove-section-$(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.

---
base-commit: cfc584537150484874e10ec4e59ad2ecbae46bfe
change-id: 20251010-kbuild-fix-mod-device-syms-reloc-err-535757ed4cd5

Best regards,
--
Nathan Chancellor <nat...@kernel.org>

[Nicolas Schier]

Thanks!

Tested-by: Nicolas Schier <n...@kernel.org>