linux-kernel - Re: [tip: objtool/core] objtool: Use sh_info to find the base for .rela sections

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Message-ID: <202006161057.E6D5D84@keescook>
Date:   Tue, 16 Jun 2020 11:00:59 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>, x86 <x86@...nel.org>
Cc:     linux-tip-commits@...r.kernel.org,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [tip: objtool/core] objtool: Use sh_info to find the base for
 .rela sections

On Wed, Apr 22, 2020 at 10:24:44PM -0000, tip-bot2 for Sami Tolvanen wrote:
> The following commit has been merged into the objtool/core branch of tip:
> 
> Commit-ID:     e2ccbff8f02d6b140b8ee71108264686c19b1c78
> Gitweb:        https://git.kernel.org/tip/e2ccbff8f02d6b140b8ee71108264686c19b1c78
> Author:        Sami Tolvanen <samitolvanen@...gle.com>
> AuthorDate:    Tue, 21 Apr 2020 11:25:01 -07:00
> Committer:     Josh Poimboeuf <jpoimboe@...hat.com>
> CommitterDate: Tue, 21 Apr 2020 18:49:15 -05:00
> 
> objtool: Use sh_info to find the base for .rela sections
> 
> ELF doesn't require .rela section names to match the base section. Use
> the section index in sh_info to find the section instead of looking it
> up by name.
> 
> LLD, for example, generates a .rela section that doesn't match the base
> section name when we merge sections in a linker script for a binary
> compiled with -ffunction-sections.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> Reviewed-by: Kees Cook <keescook@...omium.org>

Hi!

Where did this commit end up? It seems to have vanished (404 on the
Gitweb link) and isn't in -next nor Linus's tree.

This is needed for LTO, FGKASLR, and link speed improvements[1]. Is it
possible to get this landed in -rc2 so all the things depending on it
can rebase happily?

Thanks!

-Kees

[1] https://lore.kernel.org/lkml/CAK7LNARbZhoaA=Nnuw0=gBrkuKbr_4Ng_Ei57uafujZf7Xazgw@mail.gmail.com/

> ---
>  tools/objtool/elf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
> index c4857fa..c20dfe1 100644
> --- a/tools/objtool/elf.c
> +++ b/tools/objtool/elf.c
> @@ -468,7 +468,7 @@ static int read_relas(struct elf *elf)
>  		if (sec->sh.sh_type != SHT_RELA)
>  			continue;
>  
> -		sec->base = find_section_by_name(elf, sec->name + 5);
> +		sec->base = find_section_by_index(elf, sec->sh.sh_info);
>  		if (!sec->base) {
>  			WARN("can't find base section for rela section %s",
>  			     sec->name);

-- 
Kees Cook