First of all, I'd strongly suggest you trim your emails when you reply -
that would be much appreciated.
On Wed, Apr 07, 2021 at 07:24:54AM +0200, Christophe Leroy wrote:
> > @@ -258,7 +240,7 @@ static int sev_issue_cmd(struct kvm *kvm, int id, void *data, int *error)
> > static int sev_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
> > {
> > struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> > - struct sev_data_launch_start *start;
> > + struct sev_data_launch_start start;
>
> struct sev_data_launch_start start = {0, 0, 0, 0, 0, 0, 0};
I don't know how this is any better than using memset...
Also, you can do
... start = { };
which is certainly the only other alternative to memset, AFAIK.
But whatever you do, you need to look at the resulting asm the compiler
generates. So let's do that:
Your version:
# arch/x86/kvm/svm/sev.c:261: struct sev_data_launch_start _tmp = {0, 0, 0, 0, 0, 0, 0};
movq $0, 104(%rsp) #, MEM[(struct sev_data_launch_start *)_561]
movq $0, 112(%rsp) #, MEM[(struct sev_data_launch_start *)_561]
movq $0, 120(%rsp) #, MEM[(struct sev_data_launch_start *)_561]
movq $0, 128(%rsp) #, MEM[(struct sev_data_launch_start *)_561]
movl $0, 136(%rsp) #, MEM[(struct sev_data_launch_start *)_561]
my version:
# arch/x86/kvm/svm/sev.c:261: struct sev_data_launch_start _tmp = {};
movq $0, 104(%rsp) #, MEM[(struct sev_data_launch_start *)_561]
movq $0, 112(%rsp) #, MEM[(struct sev_data_launch_start *)_561]
movq $0, 120(%rsp) #, MEM[(struct sev_data_launch_start *)_561]
movq $0, 128(%rsp) #, MEM[(struct sev_data_launch_start *)_561]
movl $0, 136(%rsp) #, MEM[(struct sev_data_launch_start *)_561]
the memset version:
# arch/x86/kvm/svm/sev.c:269: memset(&_tmp, 0, sizeof(_tmp));
#NO_APP
movq $0, 104(%rsp) #, MEM <char[1:36]> [(void *)_561]
movq $0, 112(%rsp) #, MEM <char[1:36]> [(void *)_561]
movq $0, 120(%rsp) #, MEM <char[1:36]> [(void *)_561]
movq $0, 128(%rsp) #, MEM <char[1:36]> [(void *)_561]
movl $0, 136(%rsp) #, MEM <char[1:36]> [(void *)_561]
Ok?
--
Regards/Gruss,
Boris.
SUSE Software Solutions Germany GmbH, GF: Felix Imendörffer, HRB 36809, AG Nürnberg
