Re: [Qemu-devel] qemu in full emulation on win32

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 19/07/12 02:35, Stefan Weil wrote:
> Am 18.07.2012 08:30, schrieb Alexey Kardashevskiy:
>> Hi!
>>
>> Found 2 problems while I was debugging qemu/ppc64-softmmu/qemu-system-ppc64.exe
>> WindowsXP SP3 Pro, 32bit, i686-pc-mingw32-gcc (GCC) 4.5.2.
>>
>>
>> 1. The size of the following is 7 bytes on linux and 8 bytes on Windows:
>> struct {
>>      uint32_t hi;
>>      uint64_t child;
>>      uint64_t parent;
>>      uint64_t size;
>> } __attribute__((packed)) ranges[];
>>
>> The structure is used between QEMU and Open Firmware (powerpc bios) so it is important.
>>
>> The Feature is described here:
>> http://stackoverflow.com/questions/7789668/why-would-the-size-of-a-packed-structure-be-different-on-linux-and-windows-when
>> Shortly there is packing and ms-packing and they are different :)
>>
>> The solutions are:
>> 1. Add MS-specific #pragma pack(push,1) and #pragma pack(pop).
>> 2. Add -mno-ms-bitfields (gcc >= 4.7.0)
>> 3. Change the structure above to use only uint32_t.
>>
>> What is the common way of solving such problems in QEMU?
> 
> Problem 1 is solved with solution 4 (your own patch) although
> that patch does not change the structure size to 7 bytes :-)


The weblink here is just for explanation :)
My struct is 7 32bit values but on Windows it was 8 32bit values, 32->28 bytes.



>> 2. QEMU cannot allocate 1024MB for the guest RAM. Literally, VirtualAlloc() fails on 1024MB BUT it does not if I allocate 1023MB and 64MB by 2 subsequent calls. We allocate RAM via memory_region_init_ram(). I am pretty sure this is not happening on 64bit Windows and I suspect that it is happening with qemu-system-x86.exe, is not it?
>>
>> Do we care that there is actually enough RAM and we could allocate it in several chunks?
> 
> 
> Please try the patch which I'm going to send.
> 
> On w64, VirtualAlloc() _can_ allocate large quantities of contiguous 
> virtual memory.
> 
> On w32, it is normally restricted to the lower 2 GiB which are already 
> fragmented
> by the code (executable, shared libraries) and data. Larger quantities 
> are available
> when the executable is allowed to use the upper 2 GiB, too. That's what 
> my patch does.


Looking forward, thanks. I am surprised nobody hit it before.



-- 
Alexey