linux-kernel - Re: [PATCH v4 06/10] objtool: Handle unsorted table offset of rodata

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Message-ID: <8cb35ab7-56d0-8e8d-5e18-1bc2b94aeeeb@loongson.cn>
Date: Tue, 26 Nov 2024 21:28:19 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>, Josh Poimboeuf
 <jpoimboe@...nel.org>, Peter Zijlstra <peterz@...radead.org>
Cc: loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 06/10] objtool: Handle unsorted table offset of rodata

On 11/22/2024 12:50 PM, Tiezhu Yang wrote:
> When compling with Clang on LoongArch, there are unsorted table offset
> of rodata if there exist many jump tables, it will get the wrong table
> end and find the wrong jump destination instructions in add_jump_table(),
> so it needs to check the table size of rodata to break the process when
> parsing the relocation section of rodata.
>
> This is preparation for later patch on LoongArch, there is no effect for
> the other archs with this patch.
>
> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> ---
>  tools/objtool/check.c                 | 7 +++++++
>  tools/objtool/include/objtool/check.h | 1 +
>  2 files changed, 8 insertions(+)
>
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index b21e47d8d3d1..3b2d94c90011 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -2101,6 +2101,7 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn,
>  	struct alternative *alt;
>  	unsigned long offset;
>  	unsigned long rodata_entry_size;
> +	unsigned long rodata_table_size = insn->table_size;
>
>  	/*
>  	 * Each @reloc is a switch table relocation which points to the target
> @@ -2112,6 +2113,12 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn,
>  		if (reloc != table && reloc == next_table)
>  			break;
>
> +		/* Handle the special cases compiled with Clang on LoongArch */
> +		if (file->elf->ehdr.e_machine == EM_LOONGARCH &&
> +		    reloc->sym->type == STT_SECTION && reloc != table &&
> +		    reloc_offset(reloc) == reloc_offset(table) + rodata_table_size)
> +			break;

I think it can be generic, like this:

                 /* Check for the end of the table: */
                 if (reloc != table && reloc == next_table)
                         break;

                 if (reloc != table &&
                     reloc_offset(reloc) == reloc_offset(table) + 
rodata_table_size)
                         break;

What do you think?

Thanks,
Tiezhu