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Re: [Qemu-devel] [PATCH 2/5] trace: [all] Add "guest_vmem" event
From: |
Peter Maydell |
Subject: |
Re: [Qemu-devel] [PATCH 2/5] trace: [all] Add "guest_vmem" event |
Date: |
Thu, 17 Mar 2016 20:25:31 +0000 |
On 17 March 2016 at 19:22, Lluís Vilanova <address@hidden> wrote:
> Mmmmm, the endianness seems more of a vCPU property than one of the memory
> access. A separate event could be added for that (e.g., at vCPU
> initalization/hot-plug and whenever it is dynamically changed like in ARM).
We've chosen to implement it in QEMU as a property of the memory
access. Consider for instance instructions like x86 movbe --
sometimes an individual instruction will be a BE access even if the
CPU more usually does LE accesses. Equally, CPUs might have different
accesses for data and code, or other complicated things.
I think we're probably better off tracing as part of the memory
access the things we've implemented as memory access properties
or flags; at least that's consistent.
> For the sign extension and memory value, what about adding multiple events?
> What I did for instructions is have a simple event and one with extended
> information, so that we can tweak performance of a tracing QEMU by choosing
> one
> or the other. We could do the same for memory accesses (e.g., also show the
> memory value, sign extension and physical address).
I think the info that's in the memop value is probably worth
just printing always, it won't make much difference.
Trying to trace physaddrs is very tricky -- in the case of
a TLB hit there is no guarantee you can still identify the
physaddr of what you're accessing (the guest might have
changed the page tables and not invalidated the TLB).
thanks
-- PMM
- Re: [Qemu-devel] [PATCH 2/5] trace: [all] Add "guest_vmem" event, Peter Maydell, 2016/03/16
- Re: [Qemu-devel] [PATCH 2/5] trace: [all] Add "guest_vmem" event, Lluís Vilanova, 2016/03/17
- Re: [Qemu-devel] [PATCH 2/5] trace: [all] Add "guest_vmem" event, Richard Henderson, 2016/03/17
- Re: [Qemu-devel] [PATCH 2/5] trace: [all] Add "guest_vmem" event,
Peter Maydell <=
- Re: [Qemu-devel] [PATCH 2/5] trace: [all] Add "guest_vmem" event, Lluís Vilanova, 2016/03/18
- Re: [Qemu-devel] [PATCH 2/5] trace: [all] Add "guest_vmem" event, Peter Maydell, 2016/03/19
- Re: [Qemu-devel] [PATCH 2/5] trace: [all] Add "guest_vmem" event, Lluís Vilanova, 2016/03/20
- Re: [Qemu-devel] [PATCH 2/5] trace: [all] Add "guest_vmem" event, Peter Maydell, 2016/03/20
- Re: [Qemu-devel] [PATCH 2/5] trace: [all] Add "guest_vmem" event, Lluís Vilanova, 2016/03/21