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)