Messages in this thread Patch in this message | | | Date | Fri, 29 Sep 2017 15:46:09 -0500 | From | Josh Poimboeuf <> | Subject | Re: Problems compiling with KCFLAGS="-frecord-gcc-switches" |
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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)
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