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

[Peter Maydell]

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.

-- PMM