Re: [Qemu-devel] passing translated address out in QEMU

[Xin Tong]

On Thu, Aug 23, 2012 at 8:52 AM, Peter Maydell <address@hidden> wrote:
> On 23 August 2012 16:34, Xin Tong <address@hidden> wrote:
>> I am emulating arm on x86. i want to track the virt and physical
>> address of last memory operation. so i put 2 fields in the CPUState
>> and make tcg_global_mem_new_i32 on them Therefore, before every
>> translation i generate code to save the virtual address as follow:
>>
>> static inline void gen_st32(TCGv val, TCGv addr, int index)
>> {
>>     tcg_gen_mov_i32(cpu_last_vaddr, addr);
>>     tcg_gen_qemu_st32(val, addr, index);
>>    // tcg_gen_mov_i32(cpu_last_paddr, addr);
>>     tcg_temp_free_i32(val);
>> }
>>
>> But i do not know how to save the physical, as the physical address is
>> never passed out of tcg_gen_qemu_st32. what would be the best way to
>> get the physical address here ? i want to pass it out by the "TCGv
>> addr here" but it did not work ...
>
> This is quite difficult because our fast-path code doesn't actually
> deal with the guest physical address at all: we create a TLB which
> maps directly from guest virtual address to host virtual address
> and use that most of the time.
>
> In general you are running into the problem that QEMU is designed
> to run code fast, not to be easy to instrument.

even that. is it possible to pass host virtual out. the fast path add
the addend to get host virtual ? so it must be in a register, most
likely eax in i386. what do you think would be the best way to get
that out ?

Xin

>
> -- PMM