[PATCH v2] arch: fix broken BuildID for arm64 and riscv

[Palmer Dabbelt]

On Mon, 26 Dec 2022 10:45:37 PST (-0800), masahiroy at kernel.org wrote:
> Dennis Gilmore reports that the BuildID is missing in the arm64 vmlinux
> since commit 994b7ac1697b ("arm64: remove special treatment for the
> link order of head.o").
>
> The issue is that the type of .notes section, which contains the BuildID,
> changed from NOTES to PROGBITS.
>
> Ard Biesheuvel figured out that whichever object gets linked first gets
> to decide the type of a section. The PROGBITS type is the result of the
> compiler emitting .note.GNU-stack as PROGBITS rather than NOTE.
>
> While Ard provided a fix for arm64, I want to fix this globally because
> the same issue is happening on riscv since commit 2348e6bf4421 ("riscv:
> remove special treatment for the link order of head.o"). This problem
> will happen in general for other architectures if they start to drop
> unneeded entries from scripts/head-object-list.txt.
>
> Discard .note.GNU-stack in include/asm-generic/vmlinux.lds.h.
>
> Link: https://lore.kernel.org/lkml/CAABkxwuQoz1CTbyb57n0ZX65eSYiTonFCU8-LCQc=74D=xE=rA@mail.gmail.com/
> Fixes: 994b7ac1697b ("arm64: remove special treatment for the link order of head.o")
> Fixes: 2348e6bf4421 ("riscv: remove special treatment for the link order of head.o")
> Reported-by: Dennis Gilmore <dennis at ausil.us>
> Suggested-by: Ard Biesheuvel <ardb at kernel.org>
> Signed-off-by: Masahiro Yamada <masahiroy at kernel.org>
> ---
>
> Changes in v2:
>   - discard .note.GNU-stack before .notes because many architectures
>     call DISCARDS at the end of their linker scripts
>
>  include/asm-generic/vmlinux.lds.h | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index a94219e9916f..659bf3b31c91 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -891,7 +891,12 @@
>  #define PRINTK_INDEX
>  #endif
>
> +/*
> + * Discard .note.GNU-stack, which is emitted as PROGBITS by the compiler.
> + * Otherwise, the type of .notes section would become PROGBITS instead of NOTES.
> + */
>  #define NOTES								\
> +	/DISCARD/ : { *(.note.GNU-stack) }				\
>  	.notes : AT(ADDR(.notes) - LOAD_OFFSET) {			\
>  		BOUNDED_SECTION_BY(.note.*, _notes)			\
>  	} NOTES_HEADERS							\

Acked-by: Palmer Dabbelt <palmer at rivosinc.com>

Thanks!