"ld.lld: error: section type mismatch for .plt" after LLVM commit 66f8ac8d3604d67599734c3fd272032e9448aca2

[nathanchance]

llvm/llvm-project@66f8ac8

As I reported on Phabricator, linking modules with ld.lld when CONFIG_ARM64_MODULE_PLTS is enabled is now broken:

$ make -skj"$(nproc)" ARCH=arm64 LLVM=1 mrproper defconfig all
...
ld.lld: error: section type mismatch for .plt
>>> <internal>:(.plt): SHT_PROGBITS
>>> output section .plt: SHT_NOBITS
...

The following change was suggested on Phabricator, which builds, but I am not sure what the runtime implications of this are.

diff --git a/arch/arm64/include/asm/module.lds.h b/arch/arm64/include/asm/module.lds.h
index a11ccadd47d2..2c9a5219aa33 100644
--- a/arch/arm64/include/asm/module.lds.h
+++ b/arch/arm64/include/asm/module.lds.h
@@ -1,6 +1,6 @@
 SECTIONS {
 #ifdef CONFIG_ARM64_MODULE_PLTS
-       .plt 0 (NOLOAD) : { BYTE(0) }
+       .plt 0 : { BYTE(0) }
        .init.plt 0 (NOLOAD) : { BYTE(0) }
        .text.ftrace_trampoline 0 (NOLOAD) : { BYTE(0) }
 #endif

[nathanchance]

Fangrui sent https://lore.kernel.org/r/20220218081209.354383-1-maskray@google.com/.

I requested the removal of this error until the kernel can be fully patched so that groups like LKFT and 0day do not get bitten by this: https://reviews.llvm.org/D118840#3332118

[nickdesaulniers]

@MaskRay also sent https://lore.kernel.org/linux-riscv/20220218082611.396353-1-maskray@google.com/ for riscv.

[MaskRay]

@nathanchance Will a warning be fine? The link still proceeds.

[nathanchance]

@nathanchance Will a warning be fine? The link still proceeds.

Yes, I think a warning would be fine. Groups might still notice but I think it is better than outright breaking the build and we will still push forward with your patch or @ardbiesheuvel's suggestion to get it cleaned up.

[MaskRay]

@nathanchance Will a warning be fine? The link still proceeds.

Yes, I think a warning would be fine. Groups might still notice but I think it is better than outright breaking the build and we will still push forward with your patch or @ardbiesheuvel's suggestion to get it cleaned up.

Thanks! llvm/llvm-project@cb0a4bb changed (NOLOAD) mismatch to a warning.

[nathanchance]

Thanks! llvm/llvm-project@cb0a4bb changed (NOLOAD) mismatch to a warning.

Thank you a lot for the compromise and sending the fixes! We'll make sure they get picked up and backported, hopefully in a timely manner.

[nathanchance]

arm64 patch has been accepted: https://git.kernel.org/arm64/c/4013e26670c590944abdab56c4fa797527b74325

[nickdesaulniers]

commit 4013e26 ("arm64: module: remove (NOLOAD) from linker script")
is now in 5.18-rc1 (when rc1 gets tagged).

So just waiting on the riscv change to hit mainline before closing (though maybe we'll need backports).

[nickdesaulniers]

riscv accepted: https://git.kernel.org/pub/scm/linux/kernel/git/palmer/linux.git/commit/?id=60210a3d86dc57ce4a76a366e7841dda746a33f7