linux-kernel - Re: [PATCH kernel] vfio-pci/nvlink2: Fix ancient gcc warnings

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Date:   Tue, 22 Jan 2019 21:30:43 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Alexey Kardashevskiy <aik@...abs.ru>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     linuxppc-dev@...ts.ozlabs.org, kvm@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH kernel] vfio-pci/nvlink2: Fix ancient gcc warnings

Hi Geert,

The below patch comes about from the build regressions and improvements
list you've sent out, but something doesn't add up that we'd be testing
with an old compiler where initialization with { 0 } generates a
"missing braces around initialization" warning.  Is this really the
case or are we missing something here?  There's no harm that I can see
with Alexey's fix, but are these really just false positives from a
compiler bug that we should selectively ignore if the "fix" is less
clean?  Thanks,

Alex

On Wed, 23 Jan 2019 15:07:11 +1100
Alexey Kardashevskiy <aik@...abs.ru> wrote:

> Using the {0} construct as a generic initializer is perfectly fine in C,
> however due to a bug in old gcc there is a warning:
> 
>   + /kisskb/src/drivers/vfio/pci/vfio_pci_nvlink2.c: warning: (near
> initialization for 'cap.header') [-Wmissing-braces]:  => 181:9
> 
> Since for whatever reason we still want to compile the modern kernel
> with such an old gcc without warnings, this changes the capabilities
> initialization.
> 
> The gcc bugzilla: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53119
> 
> Signed-off-by: Alexey Kardashevskiy <aik@...abs.ru>
> ---
>  drivers/vfio/pci/vfio_pci_nvlink2.c | 30 ++++++++++++++---------------
>  1 file changed, 15 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_nvlink2.c b/drivers/vfio/pci/vfio_pci_nvlink2.c
> index 054a2cf..91d945b 100644
> --- a/drivers/vfio/pci/vfio_pci_nvlink2.c
> +++ b/drivers/vfio/pci/vfio_pci_nvlink2.c
> @@ -178,11 +178,11 @@ static int vfio_pci_nvgpu_add_capability(struct vfio_pci_device *vdev,
>  		struct vfio_pci_region *region, struct vfio_info_cap *caps)
>  {
>  	struct vfio_pci_nvgpu_data *data = region->data;
> -	struct vfio_region_info_cap_nvlink2_ssatgt cap = { 0 };
> -
> -	cap.header.id = VFIO_REGION_INFO_CAP_NVLINK2_SSATGT;
> -	cap.header.version = 1;
> -	cap.tgt = data->gpu_tgt;
> +	struct vfio_region_info_cap_nvlink2_ssatgt cap = {
> +		.header.id = VFIO_REGION_INFO_CAP_NVLINK2_SSATGT,
> +		.header.version = 1,
> +		.tgt = data->gpu_tgt
> +	};
>  
>  	return vfio_info_add_capability(caps, &cap.header, sizeof(cap));
>  }
> @@ -365,18 +365,18 @@ static int vfio_pci_npu2_add_capability(struct vfio_pci_device *vdev,
>  		struct vfio_pci_region *region, struct vfio_info_cap *caps)
>  {
>  	struct vfio_pci_npu2_data *data = region->data;
> -	struct vfio_region_info_cap_nvlink2_ssatgt captgt = { 0 };
> -	struct vfio_region_info_cap_nvlink2_lnkspd capspd = { 0 };
> +	struct vfio_region_info_cap_nvlink2_ssatgt captgt = {
> +		.header.id = VFIO_REGION_INFO_CAP_NVLINK2_SSATGT,
> +		.header.version = 1,
> +		.tgt = data->gpu_tgt
> +	};
> +	struct vfio_region_info_cap_nvlink2_lnkspd capspd = {
> +		.header.id = VFIO_REGION_INFO_CAP_NVLINK2_LNKSPD,
> +		.header.version = 1,
> +		.link_speed = data->link_speed
> +	};
>  	int ret;
>  
> -	captgt.header.id = VFIO_REGION_INFO_CAP_NVLINK2_SSATGT;
> -	captgt.header.version = 1;
> -	captgt.tgt = data->gpu_tgt;
> -
> -	capspd.header.id = VFIO_REGION_INFO_CAP_NVLINK2_LNKSPD;
> -	capspd.header.version = 1;
> -	capspd.link_speed = data->link_speed;
> -
>  	ret = vfio_info_add_capability(caps, &captgt.header, sizeof(captgt));
>  	if (ret)
>  		return ret;