[PATCH] objtool: use sh_info to find the base for .rela sections

[PATCH] objtool: use sh_info to find the base for .rela sections

[Sami Tolvanen]

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@google.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 09ddc8f1def3..73cfe45975c8 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);

base-commit: ae83d0b416db002fe95601e7f97f64b59514d936
-- 
2.26.1.301.g55bc3eb7cb9-goog

Re: [PATCH] objtool: use sh_info to find the base for .rela sections

[Kees Cook]

On Tue, Apr 21, 2020 at 11:25:01AM -0700, Sami Tolvanen wrote:
> 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@google.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  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 09ddc8f1def3..73cfe45975c8 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);
> 
> base-commit: ae83d0b416db002fe95601e7f97f64b59514d936
> -- 
> 2.26.1.301.g55bc3eb7cb9-goog
> 

-- 
Kees Cook