linux-kernel - Re: [PATCH] arch: fix broken BuildID for arm64 and riscv

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Message-ID: <Y6hptEk8FmISixLS@spud>
Date:   Sun, 25 Dec 2022 15:18:12 +0000
From:   Conor Dooley <conor@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-arch@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, Dennis Gilmore <dennis@...il.us>,
        Albert Ou <aou@...s.berkeley.edu>,
        Arnd Bergmann <arnd@...db.de>,
        Jisheng Zhang <jszhang@...nel.org>,
        Nicolas Schier <nicolas@...sle.eu>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>
Subject: Re: [PATCH] arch: fix broken BuildID for arm64 and riscv

On Sun, Dec 25, 2022 at 04:27:51AM +0900, Masahiro Yamada 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, and 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.
> 
> riscv needs to change its linker script so that DISCARDS comes before
> the .notes section.

Hey Mashiro,

No idea why I decided to look at patchwork today, but this seems to
break the build on RISC-V, there's a whole load of the following in the
output:
`.LPFE4' referenced in section `__patchable_function_entries' of kernel/trace/trace_selftest_dynamic.o: defined in discarded section `.text.exit' of kernel/trace/trace_selftest_dynamic.o

I assume that's what's doing it, but given the day that's in it - I
haven't looked into this any further, nor gone and fished the logs out of
the builder.

Thanks,
Conor.

> 
> 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@...il.us>
> Suggested-by: Ard Biesheuvel <ardb@...nel.org>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---
> 
>  arch/riscv/kernel/vmlinux.lds.S   | 4 ++--
>  include/asm-generic/vmlinux.lds.h | 1 +
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
> index 4e6c88aa4d87..1865a258e560 100644
> --- a/arch/riscv/kernel/vmlinux.lds.S
> +++ b/arch/riscv/kernel/vmlinux.lds.S
> @@ -31,6 +31,8 @@ PECOFF_FILE_ALIGNMENT = 0x200;
>  
>  SECTIONS
>  {
> +	DISCARDS
> +
>  	/* Beginning of code and text segment */
>  	. = LOAD_OFFSET;
>  	_start = .;
> @@ -141,7 +143,5 @@ SECTIONS
>  	STABS_DEBUG
>  	DWARF_DEBUG
>  	ELF_DETAILS
> -
> -	DISCARDS
>  }
>  #endif /* CONFIG_XIP_KERNEL */
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index a94219e9916f..2993b790fe98 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -1007,6 +1007,7 @@
>  	*(.modinfo)							\
>  	/* ld.bfd warns about .gnu.version* even when not emitted */	\
>  	*(.gnu.version*)						\
> +	*(.note.GNU-stack)	/* emitted as PROGBITS */
>  
>  #define DISCARDS							\
>  	/DISCARD/ : {							\
> -- 
> 2.34.1
> 

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