Re: [PATCH 1 of 3] Remove use of bit fields in kvm trace structure

Hollis Blanchard
2008-06-20T16:59:32Z

Slightly unconventional coding style, but Acked-by: Hollis Blanchard
<hollisb@us.ibm.com>

Eric, as I mentioned previously, bitfields cannot be used in portable
binary formats.

Avi, would you apply please?
﻿
--
Hollis Blanchard
IBM Linux Technology Center

On Thu, 2008-06-19 at 23:19 -0500, Jerone Young wrote:
> 2 files changed, 21 insertions(+), 11 deletions(-)
> include/linux/kvm.h | 10 +++++++---
> virt/kvm/kvm_trace.c | 22 ++++++++++++++--------
>
>
> This patch fixes kvmtrace use on big endian systems. When using bit fields the compiler will lay data out in the wrong order expected when laid down into a file. This fixes it by using one variable instead of using bit fields.
>
> Signed-off-by: Jerone Young <jyoung5@us.ibm.com>
>
> diff --git a/include/linux/kvm.h b/include/linux/kvm.h
> --- a/include/linux/kvm.h
> +++ b/include/linux/kvm.h
> @@ -311,9 +311,13 @@ struct kvm_s390_interrupt {
>
> /* This structure represents a single trace buffer record. */
> struct kvm_trace_rec {
> - __u32 event:28;
> - __u32 extra_u32:3;
> - __u32 cycle_in:1;
> + /* variable rec_val
> + * is split into:
> + * bits 0 - 27 -> event id
> + * bits 28 -30 -> number of extra data args of size u32
> + * bits 31 -> binary indicator for if tsc is in record
> + */
> + __u32 rec_val;
> __u32 pid;
> __u32 vcpu_id;
> union {
> diff --git a/virt/kvm/kvm_trace.c b/virt/kvm/kvm_trace.c
> --- a/virt/kvm/kvm_trace.c
> +++ b/virt/kvm/kvm_trace.c
> @@ -54,12 +54,15 @@ static void kvm_add_trace(void *probe_pr
> struct kvm_trace *kt = kvm_trace;
> struct kvm_trace_rec rec;
> struct kvm_vcpu *vcpu;
> - int i, extra, size;
> + int i, size;
> + u32 extra;
>
> if (unlikely(kt->trace_state != KVM_TRACE_STATE_RUNNING))
> return;
> +
> + /* set event id */
> + rec.rec_val = 0x0fffffff & va_arg(*args, u32);
>
> - rec.event = va_arg(*args, u32);
> vcpu = va_arg(*args, struct kvm_vcpu *);
> rec.pid = current->tgid;
> rec.vcpu_id = vcpu->vcpu_id;
> @@ -67,21 +70,24 @@ static void kvm_add_trace(void *probe_pr
> extra = va_arg(*args, u32);
> WARN_ON(!(extra <= KVM_TRC_EXTRA_MAX));
> extra = min_t(u32, extra, KVM_TRC_EXTRA_MAX);
> - rec.extra_u32 = extra;
>
> - rec.cycle_in = p->cycle_in;
> + /* set inidicator for tcs record */
> + rec.rec_val |= 0x80000000 & (p->cycle_in << 31);
> +
> + /* set extra data num */
> + rec.rec_val |= 0x70000000 & (extra << 28);
>
> - if (rec.cycle_in) {
> + if (p->cycle_in) {
> rec.u.cycle.cycle_u64 = get_cycles();
>
> - for (i = 0; i < rec.extra_u32; i++)
> + for (i = 0; i < extra; i++)
> rec.u.cycle.extra_u32[i] = va_arg(*args, u32);
> } else {
> - for (i = 0; i < rec.extra_u32; i++)
> + for (i = 0; i < extra; i++)
> rec.u.nocycle.extra_u32[i] = va_arg(*args, u32);
> }
>
> - size = calc_rec_size(rec.cycle_in, rec.extra_u32 * sizeof(u32));
> + size = calc_rec_size(p->cycle_in, extra * sizeof(u32));
> relay_write(kt->rchan, &rec, size);
> }
>
> --
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