linux-kernel - [PATCH] KVM: selftests: Fix build for evmcs.h

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Date:   Mon,  4 May 2020 18:06:07 -0400
From:   Peter Xu <peterx@...hat.com>
To:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     peterx@...hat.com, Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: [PATCH] KVM: selftests: Fix build for evmcs.h

I got this error when building kvm selftests:

/usr/bin/ld: /home/xz/git/linux/tools/testing/selftests/kvm/libkvm.a(vmx.o):/home/xz/git/linux/tools/testing/selftests/kvm/include/evmcs.h:222: multiple definition of `current_evmcs'; /tmp/cco1G48P.o:/home/xz/git/linux/tools/testing/selftests/kvm/include/evmcs.h:222: first defined here
/usr/bin/ld: /home/xz/git/linux/tools/testing/selftests/kvm/libkvm.a(vmx.o):/home/xz/git/linux/tools/testing/selftests/kvm/include/evmcs.h:223: multiple definition of `current_vp_assist'; /tmp/cco1G48P.o:/home/xz/git/linux/tools/testing/selftests/kvm/include/evmcs.h:223: first defined here

I think it's because evmcs.h is included both in a test file and a lib file so
the structs have multiple declarations when linking.  After all it's not a good
habit to declare structs in the header files.

Cc: Vitaly Kuznetsov <vkuznets@...hat.com>
Signed-off-by: Peter Xu <peterx@...hat.com>
---

I initially thought it was something about my GCC 10 upgrade that I recently
did to my laptop - gcc10 even fails the build of the latest kernel after
all (though it turns out to be a kernel bug on build system rather than a gcc
bug). but I'm not sure about this one...
---
 tools/testing/selftests/kvm/include/evmcs.h  | 4 ++--
 tools/testing/selftests/kvm/lib/x86_64/vmx.c | 3 +++
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/evmcs.h b/tools/testing/selftests/kvm/include/evmcs.h
index d8f4d6bfe05d..a034438b6266 100644
--- a/tools/testing/selftests/kvm/include/evmcs.h
+++ b/tools/testing/selftests/kvm/include/evmcs.h
@@ -219,8 +219,8 @@ struct hv_enlightened_vmcs {
 #define HV_X64_MSR_VP_ASSIST_PAGE_ADDRESS_MASK	\
 		(~((1ull << HV_X64_MSR_VP_ASSIST_PAGE_ADDRESS_SHIFT) - 1))
 
-struct hv_enlightened_vmcs *current_evmcs;
-struct hv_vp_assist_page *current_vp_assist;
+extern struct hv_enlightened_vmcs *current_evmcs;
+extern struct hv_vp_assist_page *current_vp_assist;
 
 int vcpu_enable_evmcs(struct kvm_vm *vm, int vcpu_id);
 
diff --git a/tools/testing/selftests/kvm/lib/x86_64/vmx.c b/tools/testing/selftests/kvm/lib/x86_64/vmx.c
index 6f17f69394be..4ae104f6ce69 100644
--- a/tools/testing/selftests/kvm/lib/x86_64/vmx.c
+++ b/tools/testing/selftests/kvm/lib/x86_64/vmx.c
@@ -17,6 +17,9 @@
 
 bool enable_evmcs;
 
+struct hv_enlightened_vmcs *current_evmcs;
+struct hv_vp_assist_page *current_vp_assist;
+
 struct eptPageTableEntry {
 	uint64_t readable:1;
 	uint64_t writable:1;
-- 
2.26.2