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/202211282102.QUr7HHrW-lkp@xxxxxxxxx/) 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
