Hi all,
After merging the powerpc-objtool tree, today's linux-next build (powerpc
pseries_le_defconfig) produced these warnings:
arch/powerpc/kernel/head_64.o: warning: objtool: end_first_256B(): can't find starting instruction
arch/powerpc/kernel/optprobes_head.o: warning: objtool: optprobe_template_end(): can't find starting instruction
I have no idea what started this (they may have been there yesterday).
--
Cheers,
Stephen Rothwell
Hi all,
On 25/11/22 09:00, Stephen Rothwell wrote:
> Hi all,
>
> After merging the powerpc-objtool tree, today's linux-next build (powerpc
> pseries_le_defconfig) produced these warnings:
>
> arch/powerpc/kernel/head_64.o: warning: objtool: end_first_256B(): can't find starting instruction
> arch/powerpc/kernel/optprobes_head.o: warning: objtool: optprobe_template_end(): can't find starting instruction
>
> I have no idea what started this (they may have been there yesterday).
I was able to recreate the above mentioned warnings with
pseries_le_defconfig and powernv_defconfig. The regression report also
mentions a warning
(https://lore.kernel.org/oe-kbuild-all/[email protected]/)
seen with arch/powerpc/kernel/kvm_emul.S assembly file.
[1] arch/powerpc/kernel/optprobes_head.o: warning: objtool:
optprobe_template_end(): can't find starting instruction
[2] arch/powerpc/kernel/kvm_emul.o: warning: objtool:
kvm_template_end(): can't find starting instruction
[3] arch/powerpc/kernel/head_64.o: warning: objtool: end_first_256B():
can't find starting instruction
The warnings [1] and [2] go away after adding 'nop' instruction. Below
diff fixes it for me:
diff --git a/arch/powerpc/kernel/optprobes_head.S
b/arch/powerpc/kernel/optprobes_head.S
index cd4e7bc32609..ea4e3bd82f4f 100644
--- a/arch/powerpc/kernel/optprobes_head.S
+++ b/arch/powerpc/kernel/optprobes_head.S
@@ -134,3 +134,4 @@ optprobe_template_ret:
.global optprobe_template_end
optprobe_template_end:
+ nop
diff --git a/arch/powerpc/kernel/kvm_emul.S b/arch/powerpc/kernel/kvm_emul.S
index 7af6f8b50c5d..41fd664e3ba0 100644
--- a/arch/powerpc/kernel/kvm_emul.S
+++ b/arch/powerpc/kernel/kvm_emul.S
@@ -352,3 +352,4 @@ kvm_tmp_end:
.global kvm_template_end
kvm_template_end:
+ nop
For warning [3], objtool is throwing can't find starting instruction
warning because it finds that the symbol (end_first_256B) is zero sized,
and such symbols are not added to the rbtree. I tried to fix it by
adding a 'nop' instruction (pasted diff below), but that resulted in a
kernel build failure.
diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 874efd25cc45..d48850fe159f 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -192,6 +192,7 @@ __secondary_hold:
EMIT_BUG_ENTRY 0b, __FILE__, __LINE__, 0
#endif
CLOSE_FIXED_SECTION(first_256B)
+nop
/*
* On server, we include the exception vectors code here as it
diff --git a/arch/powerpc/kernel/exceptions-64s.S
b/arch/powerpc/kernel/exceptions-64s.S
index 26f8fef53c72..f7517d443e9b 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -3104,9 +3104,13 @@ __end_interrupts:
DEFINE_FIXED_SYMBOL(__end_interrupts, virt_trampolines)
CLOSE_FIXED_SECTION(real_vectors);
+nop
CLOSE_FIXED_SECTION(real_trampolines);
+nop
CLOSE_FIXED_SECTION(virt_vectors);
+nop
CLOSE_FIXED_SECTION(virt_trampolines);
+nop
USE_TEXT_SECTION()
I'm not very sure on how to address this particular warning
(arch/powerpc/kernel/head_64.o: warning: objtool: end_first_256B():
can't find starting instruction). Given that there are no calls to
_mcount, one workaround is to skip objtool from running on
arch/powerpc/kernel/head_64.o file. The below diff works for me:
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 9b6146056e48..9ef6a040d875 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -219,3 +219,5 @@ $(obj)/vdso64_wrapper.o : $(obj)/vdso/vdso64.so.dbg
# for cleaning
subdir- += vdso
+
+OBJECT_FILES_NON_STANDARD_head_64.o := y
Thanks,
Sathvika
Le 29/11/2022 à 16:13, Sathvika Vasireddy a écrit :
> Hi all,
>
> On 25/11/22 09:00, Stephen Rothwell wrote:
>> Hi all,
>>
>> After merging the powerpc-objtool tree, today's linux-next build (powerpc
>> pseries_le_defconfig) produced these warnings:
>>
>> arch/powerpc/kernel/head_64.o: warning: objtool: end_first_256B():
>> can't find starting instruction
>> arch/powerpc/kernel/optprobes_head.o: warning: objtool:
>> optprobe_template_end(): can't find starting instruction
>>
>> I have no idea what started this (they may have been there yesterday).
> I was able to recreate the above mentioned warnings with
> pseries_le_defconfig and powernv_defconfig. The regression report also
> mentions a warning
> (https://lore.kernel.org/oe-kbuild-all/[email protected]/) seen with arch/powerpc/kernel/kvm_emul.S assembly file.
>
> [1] arch/powerpc/kernel/optprobes_head.o: warning: objtool:
> optprobe_template_end(): can't find starting instruction
> [2] arch/powerpc/kernel/kvm_emul.o: warning: objtool:
> kvm_template_end(): can't find starting instruction
> [3] arch/powerpc/kernel/head_64.o: warning: objtool: end_first_256B():
> can't find starting instruction
>
> The warnings [1] and [2] go away after adding 'nop' instruction. Below
> diff fixes it for me:
You have to add NOPs just because those labels are at the end of the
files. That's a bit odd.
I think either we are missing some kind of flagging for the symbols, or
objtool has a bug. In both cases, I'm not sure adding an artificial
'nop' is the solution. At least there should be a big hammer warning
explaining why.
>
> diff --git a/arch/powerpc/kernel/optprobes_head.S
> b/arch/powerpc/kernel/optprobes_head.S
> index cd4e7bc32609..ea4e3bd82f4f 100644
> --- a/arch/powerpc/kernel/optprobes_head.S
> +++ b/arch/powerpc/kernel/optprobes_head.S
> @@ -134,3 +134,4 @@ optprobe_template_ret:
>
> .global optprobe_template_end
> optprobe_template_end:
> + nop
>
> diff --git a/arch/powerpc/kernel/kvm_emul.S
> b/arch/powerpc/kernel/kvm_emul.S
> index 7af6f8b50c5d..41fd664e3ba0 100644
> --- a/arch/powerpc/kernel/kvm_emul.S
> +++ b/arch/powerpc/kernel/kvm_emul.S
> @@ -352,3 +352,4 @@ kvm_tmp_end:
>
> .global kvm_template_end
> kvm_template_end:
> + nop
>
> For warning [3], objtool is throwing can't find starting instruction
> warning because it finds that the symbol (end_first_256B) is zero sized,
> and such symbols are not added to the rbtree. I tried to fix it by
> adding a 'nop' instruction (pasted diff below), but that resulted in a
> kernel build failure.
What's the failure ?
>
> diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
> index 874efd25cc45..d48850fe159f 100644
> --- a/arch/powerpc/kernel/head_64.S
> +++ b/arch/powerpc/kernel/head_64.S
> @@ -192,6 +192,7 @@ __secondary_hold:
> EMIT_BUG_ENTRY 0b, __FILE__, __LINE__, 0
> #endif
> CLOSE_FIXED_SECTION(first_256B)
> +nop
>
> /*
> * On server, we include the exception vectors code here as it
>
> diff --git a/arch/powerpc/kernel/exceptions-64s.S
> b/arch/powerpc/kernel/exceptions-64s.S
> index 26f8fef53c72..f7517d443e9b 100644
> --- a/arch/powerpc/kernel/exceptions-64s.S
> +++ b/arch/powerpc/kernel/exceptions-64s.S
> @@ -3104,9 +3104,13 @@ __end_interrupts:
> DEFINE_FIXED_SYMBOL(__end_interrupts, virt_trampolines)
>
> CLOSE_FIXED_SECTION(real_vectors);
> +nop
> CLOSE_FIXED_SECTION(real_trampolines);
> +nop
> CLOSE_FIXED_SECTION(virt_vectors);
> +nop
> CLOSE_FIXED_SECTION(virt_trampolines);
> +nop
What are the NOPs after the CLOSE_FIXED_SECTION() ? You don't explain
them, and I can't see any related warning in the warnings you show.
>
> USE_TEXT_SECTION()
>
> I'm not very sure on how to address this particular warning
> (arch/powerpc/kernel/head_64.o: warning: objtool: end_first_256B():
> can't find starting instruction). Given that there are no calls to
> _mcount, one workaround is to skip objtool from running on
> arch/powerpc/kernel/head_64.o file. The below diff works for me:
>
> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> index 9b6146056e48..9ef6a040d875 100644
> --- a/arch/powerpc/kernel/Makefile
> +++ b/arch/powerpc/kernel/Makefile
> @@ -219,3 +219,5 @@ $(obj)/vdso64_wrapper.o : $(obj)/vdso/vdso64.so.dbg
>
> # for cleaning
> subdir- += vdso
> +
> +OBJECT_FILES_NON_STANDARD_head_64.o := y
Might be the solution, allthough I can't see other architectures doing that.
>
>
> Thanks,
> Sathvika
Christophe
On 29/11/22 20:58, Christophe Leroy wrote:
>
> Le 29/11/2022 à 16:13, Sathvika Vasireddy a écrit :
>> Hi all,
>>
>> On 25/11/22 09:00, Stephen Rothwell wrote:
>>> Hi all,
>>>
>>> After merging the powerpc-objtool tree, today's linux-next build (powerpc
>>> pseries_le_defconfig) produced these warnings:
>>>
>>> arch/powerpc/kernel/head_64.o: warning: objtool: end_first_256B():
>>> can't find starting instruction
>>> arch/powerpc/kernel/optprobes_head.o: warning: objtool:
>>> optprobe_template_end(): can't find starting instruction
>>>
>>> I have no idea what started this (they may have been there yesterday).
>> I was able to recreate the above mentioned warnings with
>> pseries_le_defconfig and powernv_defconfig. The regression report also
>> mentions a warning
>> (https://lore.kernel.org/oe-kbuild-all/[email protected]/) seen with arch/powerpc/kernel/kvm_emul.S assembly file.
>>
>> [1] arch/powerpc/kernel/optprobes_head.o: warning: objtool:
>> optprobe_template_end(): can't find starting instruction
>> [2] arch/powerpc/kernel/kvm_emul.o: warning: objtool:
>> kvm_template_end(): can't find starting instruction
>> [3] arch/powerpc/kernel/head_64.o: warning: objtool: end_first_256B():
>> can't find starting instruction
>>
>> The warnings [1] and [2] go away after adding 'nop' instruction. Below
>> diff fixes it for me:
> You have to add NOPs just because those labels are at the end of the
> files. That's a bit odd.
> I think either we are missing some kind of flagging for the symbols, or
> objtool has a bug. In both cases, I'm not sure adding an artificial
> 'nop' is the solution. At least there should be a big hammer warning
> explaining why.
I don't see these warnings with powerpc/topic/objtool branch. However,
they are seen with linux-next master branch.
Commit dbcdbdfdf137b49144204571f1a5e5dc01b8aaad objtool: Rework
instruction -> symbol mapping in linux-next is resulting in objtool
can't find starting instruction warnings on powerpc.
Reverting this particular hunk (pasted below), resolves it and we don't
see the problem anymore.
@@ -427,7 +427,10 @@ static int decode_instructions(struct objtool_file
*file)
}
list_for_each_entry(func, &sec->symbol_list, list) {
- if (func->type != STT_FUNC || func->alias != func)
+ if (func->type != STT_NOTYPE && func->type !=
STT_FUNC)
+ continue;
+
+ if (func->return_thunk || func->alias != func)
continue;
if (!find_insn(file, sec, func->offset)) {
Peterz, can we ignore STT_NOTYPE symbols?
>> diff --git a/arch/powerpc/kernel/optprobes_head.S
>> b/arch/powerpc/kernel/optprobes_head.S
>> index cd4e7bc32609..ea4e3bd82f4f 100644
>> --- a/arch/powerpc/kernel/optprobes_head.S
>> +++ b/arch/powerpc/kernel/optprobes_head.S
>> @@ -134,3 +134,4 @@ optprobe_template_ret:
>>
>> .global optprobe_template_end
>> optprobe_template_end:
>> + nop
>>
>> diff --git a/arch/powerpc/kernel/kvm_emul.S
>> b/arch/powerpc/kernel/kvm_emul.S
>> index 7af6f8b50c5d..41fd664e3ba0 100644
>> --- a/arch/powerpc/kernel/kvm_emul.S
>> +++ b/arch/powerpc/kernel/kvm_emul.S
>> @@ -352,3 +352,4 @@ kvm_tmp_end:
>>
>> .global kvm_template_end
>> kvm_template_end:
>> + nop
>>
>> For warning [3], objtool is throwing can't find starting instruction
>> warning because it finds that the symbol (end_first_256B) is zero sized,
>> and such symbols are not added to the rbtree. I tried to fix it by
>> adding a 'nop' instruction (pasted diff below), but that resulted in a
>> kernel build failure.
> What's the failure ?
>
>
>> diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
>> index 874efd25cc45..d48850fe159f 100644
>> --- a/arch/powerpc/kernel/head_64.S
>> +++ b/arch/powerpc/kernel/head_64.S
>> @@ -192,6 +192,7 @@ __secondary_hold:
>> EMIT_BUG_ENTRY 0b, __FILE__, __LINE__, 0
>> #endif
>> CLOSE_FIXED_SECTION(first_256B)
>> +nop
>>
>> /*
>> * On server, we include the exception vectors code here as it
>>
>> diff --git a/arch/powerpc/kernel/exceptions-64s.S
>> b/arch/powerpc/kernel/exceptions-64s.S
>> index 26f8fef53c72..f7517d443e9b 100644
>> --- a/arch/powerpc/kernel/exceptions-64s.S
>> +++ b/arch/powerpc/kernel/exceptions-64s.S
>> @@ -3104,9 +3104,13 @@ __end_interrupts:
>> DEFINE_FIXED_SYMBOL(__end_interrupts, virt_trampolines)
>>
>> CLOSE_FIXED_SECTION(real_vectors);
>> +nop
>> CLOSE_FIXED_SECTION(real_trampolines);
>> +nop
>> CLOSE_FIXED_SECTION(virt_vectors);
>> +nop
>> CLOSE_FIXED_SECTION(virt_trampolines);
>> +nop
> What are the NOPs after the CLOSE_FIXED_SECTION() ? You don't explain
> them, and I can't see any related warning in the warnings you show.
>
>
After fixing arch/powerpc/kernel/head_64.o: warning: objtool:
end_first_256B(): can't find starting instruction warning, objtool
started showing more warnings in the same file.
Below is the list of warnings:
arch/powerpc/kernel/head_64.o: warning: objtool: end_real_vectors():
can't find starting instruction
arch/powerpc/kernel/head_64.o: warning: objtool:
end_real_trampolines(): can't find starting instruction
arch/powerpc/kernel/head_64.o: warning: objtool: end_virt_vectors():
can't find starting instruction
arch/powerpc/kernel/head_64.o: warning: objtool:
end_virt_trampolines(): can't find starting instruction
Thanks,
Sathvika
Sathvika Vasireddy wrote:
>
> On 29/11/22 20:58, Christophe Leroy wrote:
>>
>> Le 29/11/2022 à 16:13, Sathvika Vasireddy a écrit :
>>> Hi all,
>>>
>>> On 25/11/22 09:00, Stephen Rothwell wrote:
>>>> Hi all,
>>>>
>>>> After merging the powerpc-objtool tree, today's linux-next build (powerpc
>>>> pseries_le_defconfig) produced these warnings:
>>>>
>>>> arch/powerpc/kernel/head_64.o: warning: objtool: end_first_256B():
>>>> can't find starting instruction
>>>> arch/powerpc/kernel/optprobes_head.o: warning: objtool:
>>>> optprobe_template_end(): can't find starting instruction
>>>>
>>>> I have no idea what started this (they may have been there yesterday).
>>> I was able to recreate the above mentioned warnings with
>>> pseries_le_defconfig and powernv_defconfig. The regression report also
>>> mentions a warning
>>> (https://lore.kernel.org/oe-kbuild-all/[email protected]/) seen with arch/powerpc/kernel/kvm_emul.S assembly file.
>>>
>>> [1] arch/powerpc/kernel/optprobes_head.o: warning: objtool:
>>> optprobe_template_end(): can't find starting instruction
>>> [2] arch/powerpc/kernel/kvm_emul.o: warning: objtool:
>>> kvm_template_end(): can't find starting instruction
>>> [3] arch/powerpc/kernel/head_64.o: warning: objtool: end_first_256B():
>>> can't find starting instruction
>>>
>>> The warnings [1] and [2] go away after adding 'nop' instruction. Below
>>> diff fixes it for me:
>> You have to add NOPs just because those labels are at the end of the
>> files. That's a bit odd.
>> I think either we are missing some kind of flagging for the symbols, or
>> objtool has a bug. In both cases, I'm not sure adding an artificial
>> 'nop' is the solution. At least there should be a big hammer warning
>> explaining why.
The problem looks to be that commit dbcdbdfdf137b4 ("objtool: Rework
instruction -> symbol mapping"), which was referenced by Sathvika below,
changes how STT_NOTYPE symbols are handled. In the files throwing that
warning, there are labels either at the very end of the file, or at the
end of a section with no subsequent instruction. Before that commit, we
didn't used to expect an instruction for STT_NOTYPE symbols.
>
> I don't see these warnings with powerpc/topic/objtool branch. However,
> they are seen with linux-next master branch.
> Commit dbcdbdfdf137b49144204571f1a5e5dc01b8aaad objtool: Rework
> instruction -> symbol mapping in linux-next is resulting in objtool
> can't find starting instruction warnings on powerpc.
>
> Reverting this particular hunk (pasted below), resolves it and we don't
> see the problem anymore.
>
> @@ -427,7 +427,10 @@ static int decode_instructions(struct objtool_file
> *file)
> }
>
> list_for_each_entry(func, &sec->symbol_list, list) {
> - if (func->type != STT_FUNC || func->alias != func)
> + if (func->type != STT_NOTYPE && func->type !=
> STT_FUNC)
> + continue;
> +
> + if (func->return_thunk || func->alias != func)
> continue;
>
> if (!find_insn(file, sec, func->offset)) {
We are currently bailing out if find_insn() there fails. Should we
instead just continue by not setting insn->sym?
@@ -430,11 +430,8 @@ static int decode_instructions(struct objtool_file *file)
if (func->return_thunk || func->alias != func)
continue;
- if (!find_insn(file, sec, func->offset)) {
- WARN("%s(): can't find starting instruction",
- func->name);
- return -1;
- }
+ if (!find_insn(file, sec, func->offset))
+ continue;
sym_for_each_insn(file, func, insn) {
insn->sym = func;
- Naveen