linux-kernel - Re: [PATCH 1/2] modules: Ensure natural alignment for .altinstructions and __bug

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Message-ID: <Yr82t0PQoYIcx++J@bombadil.infradead.org>
Date:   Fri, 1 Jul 2022 11:02:31 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Helge Deller <deller@....de>
Cc:     jeyu@...nel.org, linux-modules@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-parisc@...r.kernel.org,
        live-patching@...r.kernel.org
Subject: Re: [PATCH 1/2] modules: Ensure natural alignment for
 .altinstructions and __bug_table sections

On Mon, Jun 27, 2022 at 09:05:50PM +0200, Helge Deller wrote:
> In the kernel image vmlinux.lds.S linker scripts the .altinstructions
> and __bug_table sections are 32- or 64-bit aligned because they hold 32-
> and/or 64-bit values.
> 
> But for modules the module.lds.S linker script doesn't define a default
> alignment yet, so the linker chooses the default byte-alignment, which
> then leads to unnecessary unaligned memory accesses at runtime.
> 
> This patch adds the missing alignments.
> 
> Signed-off-by: Helge Deller <deller@....de>

Good catch but does this fix a real world issue? When are
altinstructions used for modules? When are alternatives used
for modules?

How did you notice this issue?

This information should go into the commit log.

  Luis
> ---
>  scripts/module.lds.S | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/scripts/module.lds.S b/scripts/module.lds.S
> index 1d0e1e4dc3d2..3a3aa2354ed8 100644
> --- a/scripts/module.lds.S
> +++ b/scripts/module.lds.S
> @@ -27,6 +27,8 @@ SECTIONS {
>  	.ctors			0 : ALIGN(8) { *(SORT(.ctors.*)) *(.ctors) }
>  	.init_array		0 : ALIGN(8) { *(SORT(.init_array.*)) *(.init_array) }
> 
> +	.altinstructions	0 : ALIGN(8) { KEEP(*(.altinstructions)) }
> +	__bug_table		0 : ALIGN(8) { KEEP(*(__bug_table)) }
>  	__jump_table		0 : ALIGN(8) { KEEP(*(__jump_table)) }
> 
>  	__patchable_function_entries : { *(__patchable_function_entries) }
> --
> 2.35.3
>