Re: [PATCH] s390/decompresser: fix misaligned symbol build error

[Nathan Chancellor]

On Thu, Jun 22, 2023 at 02:55:08PM +0200, Heiko Carstens wrote:
> Nathan Chancellor reported a kernel build error on Fedora 39:
> 
> $ clang --version | head -1
> clang version 16.0.5 (Fedora 16.0.5-1.fc39)
> 
> $ s390x-linux-gnu-ld --version | head -1
> GNU ld version 2.40-1.fc39
> 
> $ make -skj"$(nproc)" ARCH=s390 CC=clang CROSS_COMPILE=s390x-linux-gnu- olddefconfig all
> s390x-linux-gnu-ld: arch/s390/boot/startup.o(.text+0x5b4): misaligned symbol `_decompressor_end' (0x35b0f) for relocation R_390_PC32DBL
> make[3]: *** [.../arch/s390/boot/Makefile:78: arch/s390/boot/vmlinux] Error 1
> 
> It turned out that the problem with misaligned symbols on s390 was fixed
> with commit 80ddf5ce1c92 ("s390: always build relocatable kernel") for the
> kernel image, but did not take into account that the decompressor uses its
> own set of CFLAGS, which come without -fPIE.
> 
> Add the -fPIE flag also to the decompresser CFLAGS to fix this.
> 

I think this should also have:

Reported-by: CKI <cki-project@xxxxxxxxxx>
Link: https://lore.kernel.org/32935.123062114500601371@xxxxxxxxxxxxxxxxxxxxxxxx/

I technically just forwarded the report and did a little extra testing.

> Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> Suggested-by: Ulrich Weigand <Ulrich.Weigand@xxxxxxxxxx>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1747
> Signed-off-by: Heiko Carstens <hca@xxxxxxxxxxxxx>

Thanks for the quick patch, this fixes the error and I did a simple boot
test in QEMU with the resulting kernel, which showed no issues.

Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx>

> ---
>  arch/s390/Makefile | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/s390/Makefile b/arch/s390/Makefile
> index ed646c583e4f..5ed242897b0d 100644
> --- a/arch/s390/Makefile
> +++ b/arch/s390/Makefile
> @@ -27,6 +27,7 @@ KBUILD_CFLAGS_DECOMPRESSOR += -fno-delete-null-pointer-checks -msoft-float -mbac
>  KBUILD_CFLAGS_DECOMPRESSOR += -fno-asynchronous-unwind-tables
>  KBUILD_CFLAGS_DECOMPRESSOR += -ffreestanding
>  KBUILD_CFLAGS_DECOMPRESSOR += -fno-stack-protector
> +KBUILD_CFLAGS_DECOMPRESSOR += -fPIE
>  KBUILD_CFLAGS_DECOMPRESSOR += $(call cc-disable-warning, address-of-packed-member)
>  KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_DEBUG_INFO),-g)
>  KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_DEBUG_INFO_DWARF4), $(call cc-option, -gdwarf-4,))
> -- 
> 2.39.2
>