Messages in this thread Patches in this message | | | Date | Tue, 29 Nov 2022 20:43:25 +0530 | Subject | Re: linux-next: build warnings after merge of the powerpc-objtool tree | From | Sathvika Vasireddy <> |
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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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