loongarch ld.lld warning from libstub after enabling CONFIG_UNWINDER_ORC #2023

nathanchance · 2024-05-16T15:55:31Z

After commit 9f4047a4c9ca ("LoongArch: Update Loongson-3 default config file") in -next, I see a warning when linking the EFI stub:

$ make -skj"$(nproc)" ARCH=loongarch LLVM=1 defconfig all
...
ld.lld: warning: drivers/firmware/efi/libstub/lib.a(vsprintf.stub.o):(.discard.unreachable+0x0): has non-ABS relocation R_LARCH_32_PCREL against symbol ''

This warning comes from the ld.lld invocation for arch/loongarch/boot/vmlinuz.efi.elf.

I think the .discard.unreachable section comes from the unreachable() in number() in drivers/firmware/efi/libstub/vsprintf.c. I don't see that section when building with GCC but perhaps that because it was able to eliminate the default case by inlining number() into vnsprintf() and further see that base should always be one of those values?

Regardless, it seems like the EFI stub's zboot.lds should be discarding .discard and .discard.*?

diff --git a/drivers/firmware/efi/libstub/zboot.lds b/drivers/firmware/efi/libstub/zboot.lds
index ac8c0ef85158..2a684fc85eda 100644
--- a/drivers/firmware/efi/libstub/zboot.lds
+++ b/drivers/firmware/efi/libstub/zboot.lds
@@ -41,7 +41,7 @@ SECTIONS
        }

        /DISCARD/ : {
-               *(.modinfo .init.modinfo)
+               *(.discard .discard.* .modinfo .init.modinfo)
        }
 }

I suspect the only reason this issue has not been seen before is because no other architecture that supports objtool has used the EFI zboot infrastructure before this point, otherwise I would have expected the same issue to potentially occur.

The text was updated successfully, but these errors were encountered:

nathanchance · 2024-05-22T17:34:39Z

Patch formally submitted: https://lore.kernel.org/20240522-efi-zboot-lds-add-discard-sections-to-discard-v1-1-6b415efa0f85@kernel.org/

When building ARCH=loongarch defconfig + CONFIG_UNWINDER_ORC=y using LLVM, there is a warning from ld.lld when linking the EFI zboot image due to the use of unreachable() in number() in vsprintf.c: ld.lld: warning: drivers/firmware/efi/libstub/lib.a(vsprintf.stub.o):(.discard.unreachable+0x0): has non-ABS relocation R_LARCH_32_PCREL against symbol '' If the compiler cannot eliminate the default case for any reason, the .discard.unreachable section will remain in the final binary but the entire point of any section prefixed with .discard is that it is only used at compile time, so it can be discarded via /DISCARD/ in a linker script. The asm-generic vmlinux.lds.h includes .discard and .discard.* in the COMMON_DISCARDS macro but that is not used for zboot.lds, as it is not a kernel image linker script. Add .discard and .discard.* to /DISCARD/ in zboot.lds, so that any sections meant to be discarded at link time are not included in the final zboot image. This issue is not specific to LoongArch, it is just the first architecture to select CONFIG_OBJTOOL, which defines annotate_unreachable() as an asm statement to add the .discard.unreachable section, and use the EFI stub. Closes: ClangBuiltLinux#2023 Signed-off-by: Nathan Chancellor <nathan@kernel.org>

When building ARCH=loongarch defconfig + CONFIG_UNWINDER_ORC=y using LLVM, there is a warning from ld.lld when linking the EFI zboot image due to the use of unreachable() in number() in vsprintf.c: ld.lld: warning: drivers/firmware/efi/libstub/lib.a(vsprintf.stub.o):(.discard.unreachable+0x0): has non-ABS relocation R_LARCH_32_PCREL against symbol '' If the compiler cannot eliminate the default case for any reason, the .discard.unreachable section will remain in the final binary but the entire point of any section prefixed with .discard is that it is only used at compile time, so it can be discarded via /DISCARD/ in a linker script. The asm-generic vmlinux.lds.h includes .discard and .discard.* in the COMMON_DISCARDS macro but that is not used for zboot.lds, as it is not a kernel image linker script. Add .discard and .discard.* to /DISCARD/ in zboot.lds, so that any sections meant to be discarded at link time are not included in the final zboot image. This issue is not specific to LoongArch, it is just the first architecture to select CONFIG_OBJTOOL, which defines annotate_unreachable() as an asm statement to add the .discard.unreachable section, and use the EFI stub. Closes: ClangBuiltLinux/linux#2023 Signed-off-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

When building ARCH=loongarch defconfig + CONFIG_UNWINDER_ORC=y using LLVM, there is a warning from ld.lld when linking the EFI zboot image due to the use of unreachable() in number() in vsprintf.c: ld.lld: warning: drivers/firmware/efi/libstub/lib.a(vsprintf.stub.o):(.discard.unreachable+0x0): has non-ABS relocation R_LARCH_32_PCREL against symbol '' If the compiler cannot eliminate the default case for any reason, the .discard.unreachable section will remain in the final binary but the entire point of any section prefixed with .discard is that it is only used at compile time, so it can be discarded via /DISCARD/ in a linker script. The asm-generic vmlinux.lds.h includes .discard and .discard.* in the COMMON_DISCARDS macro but that is not used for zboot.lds, as it is not a kernel image linker script. Add .discard and .discard.* to /DISCARD/ in zboot.lds, so that any sections meant to be discarded at link time are not included in the final zboot image. This issue is not specific to LoongArch, it is just the first architecture to select CONFIG_OBJTOOL, which defines annotate_unreachable() as an asm statement to add the .discard.unreachable section, and use the EFI stub. Closes: ClangBuiltLinux/linux#2023 Signed-off-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

When building ARCH=loongarch defconfig + CONFIG_UNWINDER_ORC=y using LLVM, there is a warning from ld.lld when linking the EFI zboot image due to the use of unreachable() in number() in vsprintf.c: ld.lld: warning: drivers/firmware/efi/libstub/lib.a(vsprintf.stub.o):(.discard.unreachable+0x0): has non-ABS relocation R_LARCH_32_PCREL against symbol '' If the compiler cannot eliminate the default case for any reason, the .discard.unreachable section will remain in the final binary but the entire point of any section prefixed with .discard is that it is only used at compile time, so it can be discarded via /DISCARD/ in a linker script. The asm-generic vmlinux.lds.h includes .discard and .discard.* in the COMMON_DISCARDS macro but that is not used for zboot.lds, as it is not a kernel image linker script. Add .discard and .discard.* to /DISCARD/ in zboot.lds, so that any sections meant to be discarded at link time are not included in the final zboot image. This issue is not specific to LoongArch, it is just the first architecture to select CONFIG_OBJTOOL, which defines annotate_unreachable() as an asm statement to add the .discard.unreachable section, and use the EFI stub. Closes: ClangBuiltLinux#2023 Signed-off-by: Nathan Chancellor <nathan@kernel.org> Acked-by: Huacai Chen <chenhuacai@loongson.cn> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

nathanchance · 2024-05-28T16:57:44Z

Patch accepted: https://git.kernel.org/efi/efi/c/5134acb15d9ef27aa2b90aad46d4e89fcef79fdc

When building ARCH=loongarch defconfig + CONFIG_UNWINDER_ORC=y using LLVM, there is a warning from ld.lld when linking the EFI zboot image due to the use of unreachable() in number() in vsprintf.c: ld.lld: warning: drivers/firmware/efi/libstub/lib.a(vsprintf.stub.o):(.discard.unreachable+0x0): has non-ABS relocation R_LARCH_32_PCREL against symbol '' If the compiler cannot eliminate the default case for any reason, the .discard.unreachable section will remain in the final binary but the entire point of any section prefixed with .discard is that it is only used at compile time, so it can be discarded via /DISCARD/ in a linker script. The asm-generic vmlinux.lds.h includes .discard and .discard.* in the COMMON_DISCARDS macro but that is not used for zboot.lds, as it is not a kernel image linker script. Add .discard and .discard.* to /DISCARD/ in zboot.lds, so that any sections meant to be discarded at link time are not included in the final zboot image. This issue is not specific to LoongArch, it is just the first architecture to select CONFIG_OBJTOOL, which defines annotate_unreachable() as an asm statement to add the .discard.unreachable section, and use the EFI stub. Closes: ClangBuiltLinux/linux#2023 Signed-off-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

nathanchance added [PATCH] Accepted A submitted patch has been accepted upstream and removed [PATCH] Submitted A patch has been submitted for review labels May 28, 2024

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loongarch ld.lld warning from libstub after enabling CONFIG_UNWINDER_ORC #2023

loongarch ld.lld warning from libstub after enabling CONFIG_UNWINDER_ORC #2023

nathanchance commented May 16, 2024

nathanchance commented May 22, 2024

nathanchance commented May 28, 2024

loongarch ld.lld warning from libstub after enabling CONFIG_UNWINDER_ORC #2023

loongarch ld.lld warning from libstub after enabling CONFIG_UNWINDER_ORC #2023

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nathanchance commented May 16, 2024

nathanchance commented May 22, 2024

nathanchance commented May 28, 2024