Change the mov in KVM_ASM_SAFE() that zeroes @vector to a movb to
make it unambiguous.
This fixes a build failure with Clang since, unlike the GNU assembler,
the LLVM integrated assembler rejects ambiguous X86 instructions that
don't have suffixes:
In file included from x86_64/hyperv_features.c:13:
include/x86_64/processor.h:825:9: error: ambiguous instructions require an explicit suffix (could be 'movb', 'movw', 'movl', or 'movq')
return kvm_asm_safe("wrmsr", "a"(val & -1u), "d"(val >> 32), "c"(msr));
^
include/x86_64/processor.h:802:15: note: expanded from macro 'kvm_asm_safe'
asm volatile(KVM_ASM_SAFE(insn) \
^
include/x86_64/processor.h:788:16: note: expanded from macro 'KVM_ASM_SAFE'
"1: " insn "\n\t" \
^
<inline asm>:5:2: note: instantiated into assembly here
mov $0, 15(%rsp)
^
It seems like this change could introduce undesirable behavior in the
future, e.g. if someone used a type larger than a u8 for @vector, since
KVM_ASM_SAFE() will only zero the bottom byte. I tried changing the type
of @vector to an int to see what would happen. GCC failed to compile due
to a size mismatch between `movb` and `%eax`. Clang succeeded in
compiling, but the generated code looked correct, so perhaps it will not
be an issue. That being said it seems like there could be a better
solution to this issue that does not assume @vector is a u8.
Fixes: 3b23054cd3f5 ("KVM: selftests: Add x86-64 support for exception fixup")
Signed-off-by: David Matlack <dmatlack@xxxxxxxxxx>
---
tools/testing/selftests/kvm/include/x86_64/processor.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/testing/selftests/kvm/include/x86_64/processor.h b/tools/testing/selftests/kvm/include/x86_64/processor.h
index 51c6661aca77..0cbc71b7af50 100644
--- a/tools/testing/selftests/kvm/include/x86_64/processor.h
+++ b/tools/testing/selftests/kvm/include/x86_64/processor.h
@@ -786,7 +786,7 @@ void vm_install_exception_handler(struct kvm_vm *vm, int vector,
"lea 1f(%%rip), %%r10\n\t" \
"lea 2f(%%rip), %%r11\n\t" \
"1: " insn "\n\t" \
- "mov $0, %[vector]\n\t" \
+ "movb $0, %[vector]\n\t" \
"jmp 3f\n\t" \
"2:\n\t" \
"mov %%r9b, %[vector]\n\t" \
--
2.37.1.359.gd136c6c3e2-goog
