Messages in this thread Patch in this message | | | Date | Wed, 30 Nov 2022 17:21:06 +0530 | Subject | Re: linux-next: build warnings after merge of the powerpc-objtool tree | From | Sathvika Vasireddy <> |
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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@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: > 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
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