Re: [Qemu-devel] qemu log function to print out the registers of the guest

[Max Filippov]

On Tue, Aug 21, 2012 at 9:40 AM, Steven <address@hidden> wrote:
> Hi, Max,
> I wrote a small program to verify your patch could catch all the load
> instructions from the guest. However, I found some problem from the
> results.
>
> The guest OS and the emulated machine are both 32bit x86. My simple
> program in the guest declares an 1048576-element integer array,
> initialize the elements, and load them in a loop. It looks like this
>           int array[1048576];
>           initialize the array;
>
>           /*  region of interests */
>           int temp;
>           for (i=0; i < 1048576; i++) {
>               temp = array[i];
>           }
> So ideally, the path should catch the guest virtual address of in the
> loop, right?
>           In addition, the virtual address for the beginning and end
> of the array is 0xbf68b6e0 and 0xbfa8b6e0.
>           What i got is as follows
>
>           __ldl_mmu, vaddr=bf68b6e0
>           __ldl_mmu, vaddr=bf68b6e4
>           __ldl_mmu, vaddr=bf68b6e8
>           .....
>           These should be the virtual address of the above loop. The
> results look good because the gap between each vaddr is 4 bypte, which
> is the length of each element.
>           However, after certain address, I got
>
>           __ldl_mmu, vaddr=bf68bffc
>           __ldl_mmu, vaddr=bf68c000
>           __ldl_mmu, vaddr=bf68d000
>           __ldl_mmu, vaddr=bf68e000
>           __ldl_mmu, vaddr=bf68f000
>           __ldl_mmu, vaddr=bf690000
>           __ldl_mmu, vaddr=bf691000
>           __ldl_mmu, vaddr=bf692000
>           __ldl_mmu, vaddr=bf693000
>           __ldl_mmu, vaddr=bf694000
>           ...
>           __ldl_mmu, vaddr=bf727000
>           __ldl_mmu, vaddr=bf728000
>           __ldl_mmu, vaddr=bfa89000
>           __ldl_mmu, vaddr=bfa8a000
> So the rest of the vaddr I got has a different of 4096 bytes, instead
> of 4. I repeated the experiment for several times and got the same
> results. Is there anything wrong? or could you explain this? Thanks.

I see two possibilities here:
- maybe there are more fast path shortcuts in the QEMU code?
  in that case output of qemu -d op,out_asm would help.
- maybe your compiler had optimized that sample code?
  could you try to declare array in your sample as 'volatile int'?

-- 
Thanks.
-- Max