Re: [PATCH v2 11/16] media: sur40: Remove uninitialized_var() usage

Nick Desaulniers
2020-06-22T18:39:17Z

On Fri, Jun 19, 2020 at 8:30 PM Kees Cook <keescook@chromium.org> wrote:
>
> Using uninitialized_var() is dangerous as it papers over real bugs[1]
> (or can in the future), and suppresses unrelated compiler warnings (e.g.
> "unused variable"). If the compiler thinks it is uninitialized, either
> simply initialize the variable or make compiler changes. As a precursor
> to removing[2] this[3] macro[4], just remove this variable since it was
> actually unused:
>
> drivers/input/touchscreen/sur40.c:459:6: warning: variable 'packet_id' set but not used [-Wunused-but-set-variable]
> 459 | u32 packet_id;
> | ^~~~~~~~~
>
> However, in keeping with the documentation desires outlined in commit
> 335abaea7a27 ("Input: sur40 - silence unnecessary noisy debug output"),
> comment out the assignment instead of removing it.
>
> [1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/
> [2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/
> [3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/
> [4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/
>
> Fixes: 335abaea7a27 ("Input: sur40 - silence unnecessary noisy debug output")

Probably should comment out `/* u32 packet_id */` rather than removing
it then, but that doesn't really matter. Either way,
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> drivers/input/touchscreen/sur40.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/drivers/input/touchscreen/sur40.c b/drivers/input/touchscreen/sur40.c
> index 34d31c7ec8ba..620cdd7d214a 100644
> --- a/drivers/input/touchscreen/sur40.c
> +++ b/drivers/input/touchscreen/sur40.c
> @@ -456,8 +456,6 @@ static void sur40_poll(struct input_dev *input)
> {
> struct sur40_state *sur40 = input_get_drvdata(input);
> int result, bulk_read, need_blobs, packet_blobs, i;
> - u32 uninitialized_var(packet_id);
> -
> struct sur40_header *header = &sur40->bulk_in_buffer->header;
> struct sur40_blob *inblob = &sur40->bulk_in_buffer->blobs[0];
>
> @@ -491,7 +489,7 @@ static void sur40_poll(struct input_dev *input)
> if (need_blobs == -1) {
> need_blobs = le16_to_cpu(header->count);
> dev_dbg(sur40->dev, "need %d blobs\n", need_blobs);
> - packet_id = le32_to_cpu(header->packet_id);
> + /* packet_id = le32_to_cpu(header->packet_id); */
> }
>
> /*
> --
> 2.25.1
>
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--
Thanks,
~Nick Desaulniers