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Subject[PATCH] [v2] x86: kvm: avoid -Wsometimes-uninitized warning
Date
clang points out that running a 64-bit guest on a 32-bit host
would lead to uninitialized variables:

arch/x86/kvm/hyperv.c:1610:6: error: variable 'ingpa' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
if (!longmode) {
^~~~~~~~~
arch/x86/kvm/hyperv.c:1632:55: note: uninitialized use occurs here
trace_kvm_hv_hypercall(code, fast, rep_cnt, rep_idx, ingpa, outgpa);
^~~~~
arch/x86/kvm/hyperv.c:1610:2: note: remove the 'if' if its condition is always true
if (!longmode) {
^~~~~~~~~~~~~~~
arch/x86/kvm/hyperv.c:1595:18: note: initialize the variable 'ingpa' to silence this warning
u64 param, ingpa, outgpa, ret = HV_STATUS_SUCCESS;
^
= 0
arch/x86/kvm/hyperv.c:1610:6: error: variable 'outgpa' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
arch/x86/kvm/hyperv.c:1610:6: error: variable 'param' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]

Since that combination is not supported anyway, change the condition
to tell the compiler how the code is actually executed.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
v2: make the change inside of is_64_bit_mode().
---
arch/x86/kvm/hyperv.c | 6 ++----
arch/x86/kvm/x86.h | 4 ++++
2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index a39e38f13029..4c1c423a3d08 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -1594,7 +1594,7 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
{
u64 param, ingpa, outgpa, ret = HV_STATUS_SUCCESS;
uint16_t code, rep_idx, rep_cnt;
- bool fast, longmode, rep;
+ bool fast, rep;

/*
* hypercall generates UD from non zero cpl and real mode
@@ -1605,9 +1605,7 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
return 1;
}

- longmode = is_64_bit_mode(vcpu);
-
- if (!longmode) {
+ if (!is_64_bit_mode(vcpu)) {
param = ((u64)kvm_rdx_read(vcpu) << 32) |
(kvm_rax_read(vcpu) & 0xffffffff);
ingpa = ((u64)kvm_rbx_read(vcpu) << 32) |
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index e08a12892e8b..b457b3267296 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -90,6 +90,7 @@ static inline int is_long_mode(struct kvm_vcpu *vcpu)
#endif
}

+#ifdef CONFIG_X86_64
static inline bool is_64_bit_mode(struct kvm_vcpu *vcpu)
{
int cs_db, cs_l;
@@ -99,6 +100,9 @@ static inline bool is_64_bit_mode(struct kvm_vcpu *vcpu)
kvm_x86_ops->get_cs_db_l_bits(vcpu, &cs_db, &cs_l);
return cs_l;
}
+#else
+#define is_64_bit_mode(vcpu) false
+#endif

static inline bool is_la57_mode(struct kvm_vcpu *vcpu)
{
--
2.20.0
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