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Re: [Qemu-devel] [PATCH] pci: Fix compiler warning (MinGW-w64 gcc 4.9)

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH] pci: Fix compiler warning (MinGW-w64 gcc 4.9)
Date: Thu, 14 May 2015 15:06:28 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0

On 05/14/2015 02:38 PM, Stefan Weil wrote:
> i686-w64-mingw32-gcc 4.9.1 from Debian Jessie complains:
> hw/pci/pci.c:938:29: warning:
>  array subscript is above array bounds [-Warray-bounds]
> Using g_assert instead of assert fixes this warning.

Is that because the mingw headers don't properly mark the expansion of
the failed branch of assert() as noreturn, whereas g_assert() does, and
therefore the compiler has more information about what variables must be
if the rest of the function is reached?

> Signed-off-by: Stefan Weil <address@hidden>
> ---
>  hw/pci/pci.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> index 48f19a3..34f71dc 100644
> --- a/hw/pci/pci.c
> +++ b/hw/pci/pci.c
> @@ -927,8 +927,8 @@ void pci_register_bar(PCIDevice *pci_dev, int region_num,
>      uint64_t wmask;
>      pcibus_t size = memory_region_size(memory);
> -    assert(region_num >= 0);
> -    assert(region_num < PCI_NUM_REGIONS);
> +    g_assert(region_num >= 0);
> +    g_assert(region_num < PCI_NUM_REGIONS);

I must say, this is the strangest way I've ever heard of silencing a
compiler warning.  But if it works and my uneducated guess above about
why is correct,

Reviewed-by: Eric Blake <address@hidden>

Meanwhile, you may want to file a bug to the mingw maintainers that
their header is puny when compared to glibc assert() or to glib's
g_assert, when it comes to giving gcc decent hints.

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

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