linux-kernel - Re: [RFC v4 08/18] objtool: Refactor switch-tables code to support other architectures

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Message-ID: <20190822200415.t3hkjxf4m3lg5tgz@treble>
Date:   Thu, 22 Aug 2019 15:04:15 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Raphael Gault <raphael.gault@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        peterz@...radead.org, catalin.marinas@....com, will.deacon@....com,
        julien.thierry.kdev@...il.com, raph.gault+kdev@...il.com
Subject: Re: [RFC v4 08/18] objtool: Refactor switch-tables code to support
 other architectures

On Fri, Aug 16, 2019 at 01:23:53PM +0100, Raphael Gault wrote:
> The way to identify switch-tables and retrieves all the data necessary
> to handle the different execution branches is not the same on all
> architecture. In order to be able to add other architecture support,
> this patch defines arch-dependent functions to process jump-tables.
> 
> Signed-off-by: Raphael Gault <raphael.gault@....com>
> ---
>  tools/objtool/arch/arm64/arch_special.c | 15 ++++
>  tools/objtool/arch/arm64/decode.c       |  4 +-
>  tools/objtool/arch/x86/arch_special.c   | 79 ++++++++++++++++++++
>  tools/objtool/check.c                   | 95 +------------------------
>  tools/objtool/check.h                   |  7 ++
>  tools/objtool/special.h                 | 10 ++-
>  6 files changed, 114 insertions(+), 96 deletions(-)
> 
> diff --git a/tools/objtool/arch/arm64/arch_special.c b/tools/objtool/arch/arm64/arch_special.c
> index a21d28876317..17a8a06aac2a 100644
> --- a/tools/objtool/arch/arm64/arch_special.c
> +++ b/tools/objtool/arch/arm64/arch_special.c
> @@ -20,3 +20,18 @@ void arch_force_alt_path(unsigned short feature,
>  			 struct special_alt *alt)
>  {
>  }
> +
> +int arch_add_jump_table(struct objtool_file *file, struct instruction *insn,
> +			struct rela *table, struct rela *next_table)
> +{
> +	return 0;
> +}
> +
> +struct rela *arch_find_switch_table(struct objtool_file *file,
> +				  struct rela *text_rela,
> +				  struct section *rodata_sec,
> +				  unsigned long table_offset)
> +{
> +	file->ignore_unreachables = true;
> +	return NULL;
> +}

If this refactoring is done before adding arm64 support then you won't
need intermediate hacks like this.

-- 
Josh