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Message-ID: <6cdad32e-782d-5bb5-f7e9-a44fb0b6444d@linux.ibm.com>
Date: Tue, 29 Nov 2022 20:43:25 +0530
From: Sathvika Vasireddy <sv@...ux.ibm.com>
To: Stephen Rothwell <sfr@...b.auug.org.au>,
Michael Ellerman <mpe@...erman.id.au>,
PowerPC <linuxppc-dev@...ts.ozlabs.org>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linux Next Mailing List <linux-next@...r.kernel.org>,
"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
Sathvika Vasireddy <sv@...ux.ibm.com>
Subject: Re: linux-next: build warnings after merge of the powerpc-objtool
tree
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@intel.com/)
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
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