Re: [PATCH] ASoC: cros_ec_codec: fix uninitialized memory read

[Tzung-Bi Shih]

On Fri, Dec 4, 2020 at 6:55 AM Arnd Bergmann <arnd@xxxxxxxxxx> wrote:
>
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> gcc points out a memory area that is copied to a device
> but not initialized:
>
> sound/soc/codecs/cros_ec_codec.c: In function 'i2s_rx_event':
> arch/x86/include/asm/string_32.h:83:20: error: '*((void *)&p+4)' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>    83 |   *((int *)to + 1) = *((int *)from + 1);
>
> Initialize all the unused fields to zero.
>
> Fixes: 727f1c71c780 ("ASoC: cros_ec_codec: refactor I2S RX")
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>

Acked-by: Tzung-Bi Shih <tzungbi@xxxxxxxxxx>

In the case in i2s_rx_event(), only the "cmd" member is used.  But it
is fine to please the compiler.

struct __ec_align4 ec_param_ec_codec_i2s_rx {
        uint8_t cmd; /* enum ec_codec_i2s_rx_subcmd */
        uint8_t reserved[3];

        union {
            ...
        };
};

I am a bit curious about, in other use cases of
ec_param_ec_codec_i2s_rx, why the compiler doesn't complain about
uninitialization of the "reserved" member?