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

[Stefan Weil]

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 :-)


> 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.

Regards,

Stefan W.