<div dir="ltr"><div class="gmail_quote"><div dir="ltr">On Wed, Sep 12, 2018 at 10:38 AM Nick Desaulniers <<a href="mailto:ndesaulniers@google.com">ndesaulniers@google.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">On Tue, Sep 11, 2018 at 5:26 PM Nathan Chancellor<br>
<<a href="mailto:natechancellor@gmail.com" target="_blank">natechancellor@gmail.com</a>> wrote:<br>
><br>
> Clang warns if there are missing braces around a subobject<br>
> initializer.<br>
><br>
> drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c:1447:41: warning: suggest braces<br>
> around initialization of subobject [-Wmissing-braces]<br>
>                 struct amdgpu_task_info task_info = { 0 };<br>
>                                                       ^<br>
>                                                       {}<br>
> 1 warning generated.<br>
><br>
> drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c:262:41: warning: suggest braces<br>
> around initialization of subobject [-Wmissing-braces]<br>
>                 struct amdgpu_task_info task_info = { 0 };<br>
>                                                       ^<br>
>                                                       {}<br>
> 1 warning generated.<br>
><br>
> Reported-by: Nick Desaulniers <<a href="mailto:ndesaulniers@google.com" target="_blank">ndesaulniers@google.com</a>><br>
> Signed-off-by: Nathan Chancellor <<a href="mailto:natechancellor@gmail.com" target="_blank">natechancellor@gmail.com</a>><br>
> ---<br>
>  drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c | 2 +-<br>
>  drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c | 2 +-<br>
>  2 files changed, 2 insertions(+), 2 deletions(-)<br>
><br>
> diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c b/drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c<br>
> index 9333109b210d..968cc1b8cdff 100644<br>
> --- a/drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c<br>
> +++ b/drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c<br>
> @@ -1444,7 +1444,7 @@ static int gmc_v8_0_process_interrupt(struct amdgpu_device *adev,<br>
>                 gmc_v8_0_set_fault_enable_default(adev, false);<br>
><br>
>         if (printk_ratelimit()) {<br>
> -               struct amdgpu_task_info task_info = { 0 };<br>
> +               struct amdgpu_task_info task_info = { { 0 } };<br>
<br>
Hi Nathan,<br>
Thanks for this patch.  I discussed this syntax with our language<br>
lawyers.  Turns out, this is not quite correct, as you're now saying<br>
"initialize the first subobject to zero, but not the rest of the<br>
object."  -Wmissing-field-initializers would highlight this, but it's<br>
not part of -Wall.  It would be more correct to zero initialize the<br>
full struct, including all of its subobjects with `= {};`.<br></blockquote><div><br></div><div>Sorry, I think I've caused some confusion here.</div><div><br></div><div>Elements with an omitted initializer get implicitly zero-initialized. In C++, it's idiomatic to write `= {}` to perform aggregate zero-initialization, but in C, that's invalid because at least one initializer is syntactically required within the braces. As a result, `= {0}` is an idiomatic way to perform zero-initialization of an aggregate in C. Clang intends to suppress the -Wmissing-braces in that case; if the warning is still being produced in a recent version of Clang, that's a bug. However, the warning suppression was added between Clang 5 and Clang 6, so it's very plausible that the compiler being used here is simply older than the warning fix.<br></div><div><br></div><div>(Long story short: the change here seems fine, but should be unnecessary as of Clang 6.)</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
>                 amdgpu_vm_get_task_info(adev, entry->pasid, &task_info);<br>
><br>
> diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c b/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c<br>
> index 72f8018fa2a8..a781a5027212 100644<br>
> --- a/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c<br>
> +++ b/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c<br>
> @@ -259,7 +259,7 @@ static int gmc_v9_0_process_interrupt(struct amdgpu_device *adev,<br>
>         }<br>
><br>
>         if (printk_ratelimit()) {<br>
> -               struct amdgpu_task_info task_info = { 0 };<br>
> +               struct amdgpu_task_info task_info = { { 0 } };<br>
><br>
>                 amdgpu_vm_get_task_info(adev, entry->pasid, &task_info);<br>
><br>
> --<br>
> 2.18.0<br>
><br>
<br>
<br>
-- <br>
Thanks,<br>
~Nick Desaulniers<br>
</blockquote></div></div>