linux-kernel - Re: [PATCH v3 01/10] objtool: Handle various symbol types of rodata

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Message-ID: <63446b99-84f6-a51b-bee0-2f3158ecb033@loongson.cn>
Date: Tue, 19 Nov 2024 18:47:13 +0800
From: Jinyang He <hejinyang@...ngson.cn>
To: Tiezhu Yang <yangtiezhu@...ngson.cn>, 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 v3 01/10] objtool: Handle various symbol types of rodata

On 2024-11-19 14:56, Tiezhu Yang wrote:

> In the relocation section ".rela.rodata" of each .o file compiled with
> LoongArch toolchain, there are various symbol types such as STT_NOTYPE,
> STT_OBJECT, STT_FUNC in addition to the usual STT_SECTION, it needs to
> use reloc symbol offset instead of reloc addend to find the destination
> instruction in find_jump_table() and add_jump_table().
>
> This is preparation for later patch on LoongArch, there is no effect for
> the other archs with this patch.
Which patch it prepares for? Please merge some patches if it is not
independent. Otherwise I cannot find what problem it solves.
According to the commit message I think it solve some problems independent?
>
> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> ---
>   tools/objtool/check.c | 26 ++++++++++++++++++++++----
>   1 file changed, 22 insertions(+), 4 deletions(-)
>
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index 6604f5d038aa..9601235e908d 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -2079,6 +2079,7 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn,
>   	unsigned int prev_offset = 0;
>   	struct reloc *reloc = table;
>   	struct alternative *alt;
> +	unsigned long offset;
>   
>   	/*
>   	 * Each @reloc is a switch table relocation which points to the target
> @@ -2094,12 +2095,19 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn,
>   		if (prev_offset && reloc_offset(reloc) != prev_offset + 8)
>   			break;
>   
> +		if (reloc->sym->type == STT_SECTION) {
> +			/* Addend field in the relocation entry associated with the symbol */
> +			offset = reloc_addend(reloc);
> +		} else {
> +			/* The address of the symbol in the relocation entry */
> +			offset = reloc->sym->offset;
> +		}
Generally rela relocations use S + A.
> +
>   		/* Detect function pointers from contiguous objects: */
> -		if (reloc->sym->sec == pfunc->sec &&
> -		    reloc_addend(reloc) == pfunc->offset)
> +		if (reloc->sym->sec == pfunc->sec && offset == pfunc->offset)
>   			break;
>   
> -		dest_insn = find_insn(file, reloc->sym->sec, reloc_addend(reloc));
> +		dest_insn = find_insn(file, reloc->sym->sec, offset);
>   		if (!dest_insn)
>   			break;
>   
> @@ -2137,6 +2145,7 @@ static struct reloc *find_jump_table(struct objtool_file *file,
>   {
>   	struct reloc *table_reloc;
>   	struct instruction *dest_insn, *orig_insn = insn;
> +	unsigned long offset;
>   
>   	/*
>   	 * Backward search using the @first_jump_src links, these help avoid
> @@ -2160,7 +2169,16 @@ static struct reloc *find_jump_table(struct objtool_file *file,
>   		table_reloc = arch_find_switch_table(file, insn);
>   		if (!table_reloc)
>   			continue;
> -		dest_insn = find_insn(file, table_reloc->sym->sec, reloc_addend(table_reloc));
> +
> +		if (table_reloc->sym->type == STT_SECTION) {
> +			/* Addend field in the relocation entry associated with the symbol */
> +			offset = reloc_addend(table_reloc);
> +		} else {
> +			/* The address of the symbol in the relocation entry */
> +			offset = table_reloc->sym->offset;
> +		}
> +
> +		dest_insn = find_insn(file, table_reloc->sym->sec, offset);
>   		if (!dest_insn || !insn_func(dest_insn) || insn_func(dest_insn)->pfunc != func)
>   			continue;
>