On Fri, Jul 12, 2019 at 03:32:43PM +0200, Arnd Bergmann wrote:
> 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@xxxxxxxx>
> ---
> 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(-)
Reviewed-by: Roman Kagan <rkagan@xxxxxxxxxxxxx>
However I still think the log message could state it more explicitly
that it was the compiler's fault, and the patch is a workaround for it.
Otherwise later on someone may decide to restore the similarity of
is_64_bit_mode() to other inlines in this file, and will be extremely
unlikely to test clang 32-bit build...
Roman.
