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SubjectRe: [PATCH] [v3] x86: kvm: avoid -Wsometimes-uninitized warning
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On 12/07/19 16:13, Arnd Bergmann wrote:
> Clang notices a code path in which some variables are never
> initialized, but fails to figure out that this can never happen
> on i386 because is_64_bit_mode() always returns false.
>
> 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]
>
> Flip the condition around to avoid the conditional execution on i386.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> v3: reword commit log, simplify patch again
> v2: make the change inside of is_64_bit_mode().
> ---
> arch/x86/kvm/hyperv.c | 20 +++++++++-----------
> 1 file changed, 9 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index a39e38f13029..c10a8b10b203 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 +1605,14 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
> return 1;
> }
>
> - longmode = is_64_bit_mode(vcpu);
> -
> - if (!longmode) {
> +#ifdef CONFIG_X86_64
> + if (is_64_bit_mode(vcpu)) {
> + param = kvm_rcx_read(vcpu);
> + ingpa = kvm_rdx_read(vcpu);
> + outgpa = kvm_r8_read(vcpu);
> + } else
> +#endif
> + {
> param = ((u64)kvm_rdx_read(vcpu) << 32) |
> (kvm_rax_read(vcpu) & 0xffffffff);
> ingpa = ((u64)kvm_rbx_read(vcpu) << 32) |
> @@ -1615,13 +1620,6 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
> outgpa = ((u64)kvm_rdi_read(vcpu) << 32) |
> (kvm_rsi_read(vcpu) & 0xffffffff);
> }
> -#ifdef CONFIG_X86_64
> - else {
> - param = kvm_rcx_read(vcpu);
> - ingpa = kvm_rdx_read(vcpu);
> - outgpa = kvm_r8_read(vcpu);
> - }
> -#endif
>
> code = param & 0xffff;
> fast = !!(param & HV_HYPERCALL_FAST_BIT);
>

Queued, thanks.

Paolo

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