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. > > 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
