[PATCH] recordmcount: Support empty section from recent binutils

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6 messages, 3 authors, 2022-03-30 · open the first message on its own page

[PATCH] recordmcount: Support empty section from recent binutils

From: Christophe Leroy <hidden>
Date: 2021-11-24 14:44:21 

Looks like recent binutils (2.36 and over ?) may empty some section,
leading to failure like:

	Cannot find symbol for section 11: .text.unlikely.
	kernel/kexec_file.o: failed
	make[1]: *** [scripts/Makefile.build:287: kernel/kexec_file.o] Error 1

In order to avoid that, ensure that the section has a content before
returning it's name in has_rel_mcount().

Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Link: https://github.com/linuxppc/issues/issues/388
Link: https://lore.kernel.org/all/20210215162209.5e2a475b@gandalf.local.home/
Signed-off-by: Christophe Leroy <redacted>
---
 scripts/recordmcount.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/scripts/recordmcount.h b/scripts/recordmcount.h
index 1e9baa5c4fc6..cc6600b729ae 100644
--- a/scripts/recordmcount.h
+++ b/scripts/recordmcount.h
@@ -575,6 +575,8 @@ static char const *has_rel_mcount(Elf_Shdr const *const relhdr,
 				  char const *const shstrtab,
 				  char const *const fname)
 {
+	if (!shdr0->sh_size)
+		return NULL;
 	if (w(relhdr->sh_type) != SHT_REL && w(relhdr->sh_type) != SHT_RELA)
 		return NULL;
 	return __has_rel_mcount(relhdr, shdr0, shstrtab, fname);
-- 
2.33.1

Re: [PATCH] recordmcount: Support empty section from recent binutils

From: LEROY Christophe <hidden>
Date: 2021-11-26 08:45:32 


Le 24/11/2021 à 15:43, Christophe Leroy a écrit :
Looks like recent binutils (2.36 and over ?) may empty some section,
leading to failure like:

	Cannot find symbol for section 11: .text.unlikely.
	kernel/kexec_file.o: failed
	make[1]: *** [scripts/Makefile.build:287: kernel/kexec_file.o] Error 1

In order to avoid that, ensure that the section has a content before
returning it's name in has_rel_mcount().
This patch doesn't work, on PPC32 I get the following message with this 
patch applied:

[    0.000000] ftrace: No functions to be traced?

Without the patch I get:

[    0.000000] ftrace: allocating 22381 entries in 66 pages
[    0.000000] ftrace: allocated 66 pages with 2 groups

Christophe
quoted hunk
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Link: https://github.com/linuxppc/issues/issues/388
Link: https://lore.kernel.org/all/20210215162209.5e2a475b@gandalf.local.home/
Signed-off-by: Christophe Leroy <redacted>
---
  scripts/recordmcount.h | 2 ++
  1 file changed, 2 insertions(+)

diff --git a/scripts/recordmcount.h b/scripts/recordmcount.h
index 1e9baa5c4fc6..cc6600b729ae 100644
--- a/scripts/recordmcount.h
+++ b/scripts/recordmcount.h
@@ -575,6 +575,8 @@ static char const *has_rel_mcount(Elf_Shdr const *const relhdr,
  				  char const *const shstrtab,
  				  char const *const fname)
  {
+	if (!shdr0->sh_size)
+		return NULL;
  	if (w(relhdr->sh_type) != SHT_REL && w(relhdr->sh_type) != SHT_RELA)
  		return NULL;
  	return __has_rel_mcount(relhdr, shdr0, shstrtab, fname);

Re: [PATCH] recordmcount: Support empty section from recent binutils

From: Steven Rostedt <rostedt@goodmis.org>
Date: 2021-11-29 17:46:02 

On Fri, 26 Nov 2021 08:43:23 +0000
LEROY Christophe [off-list ref] wrote:

Le 24/11/2021 à 15:43, Christophe Leroy a écrit :
quoted
Looks like recent binutils (2.36 and over ?) may empty some section,
leading to failure like:

	Cannot find symbol for section 11: .text.unlikely.
	kernel/kexec_file.o: failed
	make[1]: *** [scripts/Makefile.build:287: kernel/kexec_file.o] Error 1

In order to avoid that, ensure that the section has a content before
returning it's name in has_rel_mcount().  
This patch doesn't work, on PPC32 I get the following message with this 
patch applied:

[    0.000000] ftrace: No functions to be traced?

Without the patch I get:

[    0.000000] ftrace: allocating 22381 entries in 66 pages
[    0.000000] ftrace: allocated 66 pages with 2 groups
Because of this report, I have not applied this patch (even though I was
about to push it to Linus).

I'm pulling it from my queue until this gets resolved.

Thanks,

-- Steve

Re: [PATCH] recordmcount: Support empty section from recent binutils

From: Christophe Leroy <hidden>
Date: 2021-11-29 18:02:37 


Le 29/11/2021 à 18:43, Steven Rostedt a écrit :
On Fri, 26 Nov 2021 08:43:23 +0000
LEROY Christophe [off-list ref] wrote:
quoted
Le 24/11/2021 à 15:43, Christophe Leroy a écrit :
quoted
Looks like recent binutils (2.36 and over ?) may empty some section,
leading to failure like:

	Cannot find symbol for section 11: .text.unlikely.
	kernel/kexec_file.o: failed
	make[1]: *** [scripts/Makefile.build:287: kernel/kexec_file.o] Error 1

In order to avoid that, ensure that the section has a content before
returning it's name in has_rel_mcount().
This patch doesn't work, on PPC32 I get the following message with this
patch applied:

[    0.000000] ftrace: No functions to be traced?

Without the patch I get:

[    0.000000] ftrace: allocating 22381 entries in 66 pages
[    0.000000] ftrace: allocated 66 pages with 2 groups
Because of this report, I have not applied this patch (even though I was
about to push it to Linus).

I'm pulling it from my queue until this gets resolved.
I have no idea on how to fix that for the moment.

With GCC 10 (binutils 2.36) an objdump -x on kernel/kexec_file.o gives:

0000000000000000 l    d  .text.unlikely	0000000000000000 .text.unlikely
0000000000000000  w    F .text.unlikely	0000000000000038 
.arch_kexec_apply_relocations_add
0000000000000038  w    F .text.unlikely	0000000000000038 
.arch_kexec_apply_relocations


With GCC 11 (binutils 2.37) the same gives:

0000000000000000  w    F .text.unlikely	0000000000000038 
.arch_kexec_apply_relocations_add
0000000000000038  w    F .text.unlikely	0000000000000038 
.arch_kexec_apply_relocations


The problem is that recordmcount drops weak symbols, and it doesn't find 
any non-weak symbol in .text.unlikely

Explication given at 
https://elixir.bootlin.com/linux/v5.16-rc2/source/scripts/recordmcount.h#L506

I have no idea on what to do.

Thanks
Christophe

Re: [PATCH] recordmcount: Support empty section from recent binutils

From: Joel Stanley <joel@jms.id.au>
Date: 2022-03-28 22:31:59 

On Mon, 29 Nov 2021 at 22:43, Christophe Leroy
[off-list ref] wrote:


Le 29/11/2021 à 18:43, Steven Rostedt a écrit :
quoted
On Fri, 26 Nov 2021 08:43:23 +0000
LEROY Christophe [off-list ref] wrote:
quoted
Le 24/11/2021 à 15:43, Christophe Leroy a écrit :
quoted
Looks like recent binutils (2.36 and over ?) may empty some section,
leading to failure like:

    Cannot find symbol for section 11: .text.unlikely.
    kernel/kexec_file.o: failed
    make[1]: *** [scripts/Makefile.build:287: kernel/kexec_file.o] Error 1

In order to avoid that, ensure that the section has a content before
returning it's name in has_rel_mcount().
This patch doesn't work, on PPC32 I get the following message with this
patch applied:

[    0.000000] ftrace: No functions to be traced?

Without the patch I get:

[    0.000000] ftrace: allocating 22381 entries in 66 pages
[    0.000000] ftrace: allocated 66 pages with 2 groups
Because of this report, I have not applied this patch (even though I was
about to push it to Linus).

I'm pulling it from my queue until this gets resolved.
I have no idea on how to fix that for the moment.

With GCC 10 (binutils 2.36) an objdump -x on kernel/kexec_file.o gives:

0000000000000000 l    d  .text.unlikely 0000000000000000 .text.unlikely
0000000000000000  w    F .text.unlikely 0000000000000038
.arch_kexec_apply_relocations_add
0000000000000038  w    F .text.unlikely 0000000000000038
.arch_kexec_apply_relocations


With GCC 11 (binutils 2.37) the same gives:

0000000000000000  w    F .text.unlikely 0000000000000038
.arch_kexec_apply_relocations_add
0000000000000038  w    F .text.unlikely 0000000000000038
.arch_kexec_apply_relocations


The problem is that recordmcount drops weak symbols, and it doesn't find
any non-weak symbol in .text.unlikely

Explication given at
https://elixir.bootlin.com/linux/v5.16-rc2/source/scripts/recordmcount.h#L506

I have no idea on what to do.
Did you end up finding a solution for this issue?

Cheers,

Joel

Re: [PATCH] recordmcount: Support empty section from recent binutils

From: Christophe Leroy <hidden>
Date: 2022-03-30 09:51:38 


Le 29/03/2022 à 00:31, Joel Stanley a écrit :
On Mon, 29 Nov 2021 at 22:43, Christophe Leroy
[off-list ref] wrote:
quoted


Le 29/11/2021 à 18:43, Steven Rostedt a écrit :
quoted
On Fri, 26 Nov 2021 08:43:23 +0000
LEROY Christophe [off-list ref] wrote:
quoted
Le 24/11/2021 à 15:43, Christophe Leroy a écrit :
quoted
Looks like recent binutils (2.36 and over ?) may empty some section,
leading to failure like:

     Cannot find symbol for section 11: .text.unlikely.
     kernel/kexec_file.o: failed
     make[1]: *** [scripts/Makefile.build:287: kernel/kexec_file.o] Error 1

In order to avoid that, ensure that the section has a content before
returning it's name in has_rel_mcount().
This patch doesn't work, on PPC32 I get the following message with this
patch applied:

[    0.000000] ftrace: No functions to be traced?

Without the patch I get:

[    0.000000] ftrace: allocating 22381 entries in 66 pages
[    0.000000] ftrace: allocated 66 pages with 2 groups
Because of this report, I have not applied this patch (even though I was
about to push it to Linus).

I'm pulling it from my queue until this gets resolved.
I have no idea on how to fix that for the moment.

With GCC 10 (binutils 2.36) an objdump -x on kernel/kexec_file.o gives:

0000000000000000 l    d  .text.unlikely 0000000000000000 .text.unlikely
0000000000000000  w    F .text.unlikely 0000000000000038
.arch_kexec_apply_relocations_add
0000000000000038  w    F .text.unlikely 0000000000000038
.arch_kexec_apply_relocations


With GCC 11 (binutils 2.37) the same gives:

0000000000000000  w    F .text.unlikely 0000000000000038
.arch_kexec_apply_relocations_add
0000000000000038  w    F .text.unlikely 0000000000000038
.arch_kexec_apply_relocations


The problem is that recordmcount drops weak symbols, and it doesn't find
any non-weak symbol in .text.unlikely

Explication given at
https://elixir.bootlin.com/linux/v5.16-rc2/source/scripts/recordmcount.h#L506

I have no idea on what to do.
Did you end up finding a solution for this issue?
Not really, my solution was to switch to the kernel compiler at 
https://mirrors.edge.kernel.org/pub/tools/crosstool/ which embeds 
binutils 2.36

But it looks like using objtool instead of recordmcount doesn't exhibit 
the problem.

https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20220318105140.43914-4-sv@linux.ibm.com/

Christophe
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