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

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

[tip-bot2 for Sami Tolvanen]

The following commit has been merged into the objtool/core branch of tip:

Commit-ID:     1e968bf5caf65eff3f080102879aaa5440c261b6
Gitweb:        https://git.kernel.org/tip/1e968bf5caf65eff3f080102879aaa5440c261b6
Author:        Sami Tolvanen <samitolvanen@google.com>
AuthorDate:    Tue, 21 Apr 2020 11:25:01 -07:00
Committer:     Josh Poimboeuf <jpoimboe@redhat.com>
CommitterDate: Thu, 28 May 2020 11:06:05 -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@google.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
 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 f953d3a..5bc259c 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -508,7 +508,7 @@ 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);

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

[Kees Cook]

On Tue, Jun 16, 2020 at 09:27:49PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 16, 2020 at 11:00:59AM -0700, Kees Cook wrote:
> > 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@google.com>
> > > AuthorDate:    Tue, 21 Apr 2020 11:25:01 -07:00
> > > Committer:     Josh Poimboeuf <jpoimboe@redhat.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@google.com>
> > > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> > > Reviewed-by: Kees Cook <keescook@chromium.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?
> 
> I can't remember why this happened, however I think this patch is in
> josh's objtool tree that I was going to stick in objtool/core
> tomorrow-ish.

Okay, thanks!

> Are those things you mentioned still slated for this release?

No, the three things I mentioned aren't for v5.8 (they're still under
development), but sending their respective series without the -tip
patches in -rc2 will result in redundant patches. (So, it's hardly the
end of the world, but it's just a confusing state to be in since they
appeared in -tip and then never ended up in the merge window. It'd be
helpful to have them in place for things that will base their latest
tree on v5.8-rc2.)

-- 
Kees Cook

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

[Peter Zijlstra]

On Tue, Jun 16, 2020 at 11:00:59AM -0700, Kees Cook wrote:
> 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@google.com>
> > AuthorDate:    Tue, 21 Apr 2020 11:25:01 -07:00
> > Committer:     Josh Poimboeuf <jpoimboe@redhat.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@google.com>
> > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> > Reviewed-by: Kees Cook <keescook@chromium.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?

I can't remember why this happened, however I think this patch is in
josh's objtool tree that I was going to stick in objtool/core
tomorrow-ish.

Are those things you mentioned still slated for this release?

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

[Kees Cook]

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@google.com>
> AuthorDate:    Tue, 21 Apr 2020 11:25:01 -07:00
> Committer:     Josh Poimboeuf <jpoimboe@redhat.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@google.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> Reviewed-by: Kees Cook <keescook@chromium.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

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

[tip-bot2 for Sami Tolvanen]

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@google.com>
AuthorDate:    Tue, 21 Apr 2020 11:25:01 -07:00
Committer:     Josh Poimboeuf <jpoimboe@redhat.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@google.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
 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);