Re: [PATCH] arm64: Handle .ARM.attributes section in linker scripts

[Will Deacon]

On Fri, Jan 24, 2025 at 06:31:57AM -0700, Nathan Chancellor wrote:
> A recent LLVM commit [1] started generating an .ARM.attributes section
> similar to the one that exists for 32-bit, which results in orphan
> section warnings (or errors if CONFIG_WERROR is enabled) from the linker
> because it is not handled in the arm64 linker scripts.
> 
>   ld.lld: error: arch/arm64/kernel/vdso/vgettimeofday.o:(.ARM.attributes) is being placed in '.ARM.attributes'
>   ld.lld: error: arch/arm64/kernel/vdso/vgetrandom.o:(.ARM.attributes) is being placed in '.ARM.attributes'
> 
>   ld.lld: error: vmlinux.a(lib/vsprintf.o):(.ARM.attributes) is being placed in '.ARM.attributes'
>   ld.lld: error: vmlinux.a(lib/win_minmax.o):(.ARM.attributes) is being placed in '.ARM.attributes'
>   ld.lld: error: vmlinux.a(lib/xarray.o):(.ARM.attributes) is being placed in '.ARM.attributes'
> 
> Add this new section to the necessary linker scripts to resolve the warnings.
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: b3e5d80d0c48 ("arm64/build: Warn on orphan section placement")
> Link: https://github.com/llvm/llvm-project/commit/ee99c4d4845db66c4daa2373352133f4b237c942 [1]
> Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> ---
>  arch/arm64/kernel/vdso/vdso.lds.S | 1 +
>  arch/arm64/kernel/vmlinux.lds.S   | 1 +
>  2 files changed, 2 insertions(+)

Hmm. I wonder what this new attributes section is for and how it will
co-exist with .note.gnu.property in future? For example, the spec linked
form the above commit:

https://github.com/ARM-software/abi-aa/pull/230

has references to GCS, which I don't think has a corresponding feature
bit for the ELF note (at least, Linux doesn't know about it if it does).

> diff --git a/arch/arm64/kernel/vdso/vdso.lds.S b/arch/arm64/kernel/vdso/vdso.lds.S
> index 4ec32e86a8da..f8418a3a2758 100644
> --- a/arch/arm64/kernel/vdso/vdso.lds.S
> +++ b/arch/arm64/kernel/vdso/vdso.lds.S
> @@ -75,6 +75,7 @@ SECTIONS
>  
>  	DWARF_DEBUG
>  	ELF_DETAILS
> +	.ARM.attributes 0 : { *(.ARM.attributes) }

Let's just add this to the /DISCARD/ section higher up, where we chuck
away .note.gnu.property.

> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> index f84c71f04d9e..c94942e9eb46 100644
> --- a/arch/arm64/kernel/vmlinux.lds.S
> +++ b/arch/arm64/kernel/vmlinux.lds.S
> @@ -335,6 +335,7 @@ SECTIONS
>  	STABS_DEBUG
>  	DWARF_DEBUG
>  	ELF_DETAILS
> +	.ARM.attributes 0 : { *(.ARM.attributes) }

I think we should discard this too (afaict, RO_DATA() discards
.note.gnu.property via NOTES()).

Will