Re: [Qemu-arm] How to get memroy trace in qemu-system-arm or qemu-arm

[Peter Maydell]

On 29 November 2015 at 08:30, Jimmy Situ <address@hidden> wrote:
> I am trying to capture memory access with qemu-system-arm, and I find there
> is get_phys_addr in target-arm/helper.c
> So I add a qemu trace event in it. It seems this trace can capture some
> memroy access. However, the trace address trace doses not make any sence.
>
> Do anyone know about this get_phys_addr() function. Does it call by every
> memory access?
> If not, how could I capture the memory trace correctly?

No, get_phys_addr is not called for every access:
(1) we cache the results of virtual-to-physical lookups in
a TLB, because they're expensive; subsequent TLB hits won't
call the function again
(2) direct physical address accesses won't go through the
function (for ARM this just means the memory accesses done
as part of the page table walk)

QEMU doesn't currently provide any way of tracing all guest memory
accesses, I'm afraid -- our design is more aimed at running
guest code fast, rather than providing detailed information
on things the guest is doing.

thanks
-- PMM