[PATCH] drm/vmwgfx: Zero initialize handle in vmw_execbuf_process

[PATCH] drm/vmwgfx: Zero initialize handle in vmw_execbuf_process

[Nathan Chancellor]

When building with -Wsometimes-uninitialized, Clang warns:

drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c:3964:7: warning: variable
'handle' is used uninitialized whenever '?:' condition is false
[-Wsometimes-uninitialized]

It's not wrong; however, in practice, this is never an issue because
the value of handle isn't used when user_fence_rep is NULL because
vmw_execbuf_copy_fence_user returns immediately when that is the case.
Just zero initialize this variable so that Clang no longer warns.

Link: https://github.com/ClangBuiltLinux/linux/issues/397
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
 drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
index 88b8178d4687..4ba06c2828a1 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
@@ -3829,7 +3829,7 @@ int vmw_execbuf_process(struct drm_file *file_priv,
 	struct vmw_sw_context *sw_context = &dev_priv->ctx;
 	struct vmw_fence_obj *fence = NULL;
 	struct vmw_cmdbuf_header *header;
-	uint32_t handle;
+	uint32_t handle = 0;
 	int ret;
 	int32_t out_fence_fd = -1;
 	struct sync_file *sync_file = NULL;
-- 
2.21.0

Re: [PATCH] drm/vmwgfx: Zero initialize handle in vmw_execbuf_process

[Nick Desaulniers]

On Thu, Mar 7, 2019 at 2:26 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> When building with -Wsometimes-uninitialized, Clang warns:
>
> drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c:3964:7: warning: variable
> 'handle' is used uninitialized whenever '?:' condition is false
> [-Wsometimes-uninitialized]
>
> It's not wrong; however, in practice, this is never an issue because
> the value of handle isn't used when user_fence_rep is NULL because
> vmw_execbuf_copy_fence_user returns immediately when that is the case.

Still, it's better not to conditionally pass unitialized memory to
functions.  Invariants like "don't touch this possibly unitialized
memory in THIS case" don't always pass from maintainer to maintainer.
Thanks for the patch.
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> Just zero initialize this variable so that Clang no longer warns.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/397
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> ---
>  drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
> index 88b8178d4687..4ba06c2828a1 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
> @@ -3829,7 +3829,7 @@ int vmw_execbuf_process(struct drm_file *file_priv,
>         struct vmw_sw_context *sw_context = &dev_priv->ctx;
>         struct vmw_fence_obj *fence = NULL;
>         struct vmw_cmdbuf_header *header;
> -       uint32_t handle;
> +       uint32_t handle = 0;
>         int ret;
>         int32_t out_fence_fd = -1;
>         struct sync_file *sync_file = NULL;
> --
> 2.21.0
>
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-- 
Thanks,
~Nick Desaulniers

Re: [PATCH] drm/vmwgfx: Zero initialize handle in vmw_execbuf_process

[Deepak Singh Rawat]

Hi Nathan,

Thanks for doing this. I will include this in vmwgfx-next.

Reviewed-by: Deepak Rawat <drawat@vmware.com>

On Thu, 2019-03-07 at 15:26 -0700, Nathan Chancellor wrote:
> When building with -Wsometimes-uninitialized, Clang warns:
> 
> drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c:3964:7: warning: variable
> 'handle' is used uninitialized whenever '?:' condition is false
> [-Wsometimes-uninitialized]
> 
> It's not wrong; however, in practice, this is never an issue because
> the value of handle isn't used when user_fence_rep is NULL because
> vmw_execbuf_copy_fence_user returns immediately when that is the
> case.
> Just zero initialize this variable so that Clang no longer warns.
> 
> Link: 
> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FClangBuiltLinux%2Flinux%2Fissues%2F397&amp;data=02%7C01%7Cdrawat%40vmware.com%7C6b9c429d16d844a5740c08d6a34bedb4%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C636875943916412703&amp;sdata=Yf7%2BzrbZS96yNJQewYQQ7YsHUDtJSvPaomyTJFZjsDk%3D&amp;reserved=0
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> ---
>  drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
> b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
> index 88b8178d4687..4ba06c2828a1 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
> @@ -3829,7 +3829,7 @@ int vmw_execbuf_process(struct drm_file
> *file_priv,
>  	struct vmw_sw_context *sw_context = &dev_priv->ctx;
>  	struct vmw_fence_obj *fence = NULL;
>  	struct vmw_cmdbuf_header *header;
> -	uint32_t handle;
> +	uint32_t handle = 0;
>  	int ret;
>  	int32_t out_fence_fd = -1;
>  	struct sync_file *sync_file = NULL;