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Re: [Qemu-devel] [PULL 00/16] Migration pull request (v2)

From: Eric Blake
Subject: Re: [Qemu-devel] [PULL 00/16] Migration pull request (v2)
Date: Thu, 07 May 2015 08:43:41 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0

On 05/07/2015 06:45 AM, Peter Maydell wrote:

> Fails to build on win32:
>   LINK  arm-softmmu/qemu-system-arm.exe
> arch_init.o: In function `do_compress_ram_page':
> /home/petmay01/linaro/qemu-for-merges/arch_init.c:879: undefined
> reference to `___sync_fetch_and_add_8'
> collect2: ld returned 1 exit status
> It's not valid to try to do atomic operations on a type
> that's larger than the native pointer type. (This will also
> cause compile issues on ppc32.) Unfortunately we don't
> currently have a way to make this a compile failure on
> normal 32-bit x86 setups...

Right now, patch 8/16 is the culprit:
+    atomic_inc(&acct_info.norm_pages);

which expands to:

include/qemu/atomic.h:#define atomic_inc(ptr)        ((void)
__sync_fetch_and_add(ptr, 1))

I wonder if include/qemu/atomic.h could enhance the #define wrappers to
add no-op compile-time checking, something like (untested):

#define atomic_add(ptr, n) do { \
  QEMU_BUILD_BUG_ON(sizeof(ptr) > sizeof(void*)); \
  __sync_fetch_and_add(ptr, 1); \
} while (0)

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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