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authorDavid Matlack <dmatlack@google.com>2022-07-22 23:48:38 +0000
committerPaolo Bonzini <pbonzini@redhat.com>2022-08-19 07:38:05 -0400
commit372d07084593dc7a399bf9bee815711b1fb1bcf2 (patch)
tree86739abef8b3ea7c888b80dd999576e596d22f5b /tools
parent67ef8664cc5b113f6c49b01d2a0e4cbc589623dd (diff)
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')
-rw-r--r--tools/testing/selftests/kvm/include/x86_64/processor.h2
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" \