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| author |   David Matlack <dmatlack@google.com> | 2022-07-22 23:48:38 +0000 |
|---|---|---|
| committer |   Paolo Bonzini <pbonzini@redhat.com> | 2022-08-19 07:38:05 -0400 |
| commit | 372d07084593dc7a399bf9bee815711b1fb1bcf2 (patch) | |
| tree | 86739abef8b3ea7c888b80dd999576e596d22f5b /tools/testing | |
| parent | KVM: selftests: Fix KVM_EXCEPTION_MAGIC build with Clang (diff) | |
| download | linux-dev-372d07084593dc7a399bf9bee815711b1fb1bcf2.tar.xz linux-dev-372d07084593dc7a399bf9bee815711b1fb1bcf2.zip | |
KVM: selftests: Fix ambiguous mov in KVM_ASM_SAFE()
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@google.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220722234838.2160385-3-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'tools/testing')
| -rw-r--r-- | tools/testing/selftests/kvm/include/x86_64/processor.h | 2 |
1 files changed, 1 insertions, 1 deletions
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" \ |