Messages in this thread | | | Date | Tue, 3 Oct 2017 13:00:23 -0500 | From | Josh Poimboeuf <> | Subject | Re: Problems compiling with KCFLAGS="-frecord-gcc-switches" |
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On Tue, Oct 03, 2017 at 10:54:57AM -0700, Guenter Roeck wrote: > Hi Josh, > > On Fri, Sep 29, 2017 at 03:46:09PM -0500, Josh Poimboeuf wrote: > > On Fri, Sep 29, 2017 at 01:00:56PM -0700, Guenter Roeck wrote: > > > Hi Josh, > > > > > > when trying to compile an image with KCFLAGS="-frecord-gcc-switches", > > > I get the folllowing build warning/error. > > > > > > make allmodconfig > > > KCFLAGS="-frecord-gcc-switches" make arch/x86/kvm/emulate.o > > > ./tools/objtool/objtool check --no-unreachable "arch/x86/kvm/emulate.o" > > > > > > arch/x86/kvm/emulate.o: warning: > > > objtool: .GCC.command.line+0x0: special: can't find new instruction > > > > > > Building a full image aborts with: > > > > > > WARNING: arch/x86/kvm/kvm.o(__ex_table+0x4c): Section mismatch in reference > > > from the (unknown reference) (unknown) > > > to the variable .GCC.command.line:kvm_fastop_exception > > > FATAL: The relocation at __ex_table+0x4c references > > > section ".GCC.command.line" which is not executable, IOW > > > the kernel will fault if it ever tries to > > > jump to it. Something is seriously wrong > > > and should be fixed. > > > make[2]: *** [arch/x86/kvm/kvm.o] Error 1 > > > > > > Any idea what might cause this problem ? > > > > I think this is a GCC bug with the -frecord-gcc-switches feature. Due > > to some ambiguity in some inline asm in emulate.c, it's placing some > > kernel code in the .GCC.command.line section. > > > > This seems to fix it: > > > > > > diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c > > index a36254cbf776..d90cdc77e077 100644 > > --- a/arch/x86/kvm/emulate.c > > +++ b/arch/x86/kvm/emulate.c > > @@ -425,8 +425,10 @@ static int fastop(struct x86_emulate_ctxt *ctxt, void (*fop)(struct fastop *)); > > #op " %al \n\t" \ > > FOP_RET > > > > -asm(".global kvm_fastop_exception \n" > > - "kvm_fastop_exception: xor %esi, %esi; ret"); > > +asm(".pushsection .fixup, \"ax\"\n" > > + ".global kvm_fastop_exception \n" > > + "kvm_fastop_exception: xor %esi, %esi; ret\n" > > + ".popsection"); > > > > FOP_START(setcc) > > FOP_SETCC(seto) > > Do you plan to submit a patch for this, or do you want me to do it ?
Sorry, I've been juggling a bunch of other bugs. I'll submit it soon.
-- Josh
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