linux-kernel - Re: [PATCH v2 45/62] x86/extable: Define ELF section entry size for exception tables

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Message-ID: <d6940b24-d78f-4da5-a8fa-6a408528822f@redhat.com>
Date: Wed, 28 May 2025 10:40:55 -0400
From: Joe Lawrence <joe.lawrence@...hat.com>
To: Josh Poimboeuf <jpoimboe@...nel.org>, x86@...nel.org
Cc: linux-kernel@...r.kernel.org, Petr Mladek <pmladek@...e.com>,
 Miroslav Benes <mbenes@...e.cz>, live-patching@...r.kernel.org,
 Song Liu <song@...nel.org>, laokz <laokz@...mail.com>,
 Jiri Kosina <jikos@...nel.org>, Marcos Paulo de Souza <mpdesouza@...e.com>,
 Weinan Liu <wnliu@...gle.com>, Fazla Mehrab <a.mehrab@...edance.com>,
 Chen Zhongjin <chenzhongjin@...wei.com>, Puranjay Mohan <puranjay@...nel.org>
Subject: Re: [PATCH v2 45/62] x86/extable: Define ELF section entry size for
 exception tables

On 5/9/25 4:17 PM, Josh Poimboeuf wrote:
> In preparation for the objtool klp diff subcommand, define the entry
> size for the __ex_table section in its ELF header.  This will allow
> tooling to extract individual entries.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> ---
>  arch/x86/include/asm/asm.h | 20 ++++++++++++--------
>  kernel/extable.c           |  2 ++
>  2 files changed, 14 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
> index f963848024a5..62dff336f206 100644
> --- a/arch/x86/include/asm/asm.h
> +++ b/arch/x86/include/asm/asm.h
> @@ -138,15 +138,17 @@ static __always_inline __pure void *rip_rel_ptr(void *p)
>  
>  # include <asm/extable_fixup_types.h>
>  
> +#define EXTABLE_SIZE 12
>
> + > [ ... snip ... ]
>

EXTABLE_SIZE defined in arch/x86/ ...

> diff --git a/kernel/extable.c b/kernel/extable.c
> index 71f482581cab..0ae3ee2ef266 100644
> --- a/kernel/extable.c
> +++ b/kernel/extable.c
> @@ -55,6 +55,8 @@ const struct exception_table_entry *search_exception_tables(unsigned long addr)
>  {
>  	const struct exception_table_entry *e;
>  
> +	BUILD_BUG_ON(EXTABLE_SIZE != sizeof(struct exception_table_entry));
> +

but referenced in kernel/ where a non-x86 build like ppc64le build won't
know what EXTABLE_SIZE is :(

-- 
Joe