Clang warns: sound/usb/mixer_scarlett_gen2.c:1189:32: warning: expression result unused [-Wunused-value] for (i = 0; i < count; i++, (u16 *)buf++) ^ ~~~~~ 1 warning generated. It appears the intention was to cast the void pointer to a u16 pointer so that the data could be iterated through like an array of u16 values. However, the cast happens after the increment because a cast is an rvalue, whereas the post-increment operator only works on lvalues, so the loop does not iterate as expected. Replace the post-increment shorthand with the full expression so the cast can be added in the right place and the look works as expected. Fixes: ac34df733d2d ("ALSA: usb-audio: scarlett2: Update get_config to do endian conversion") Link: https://github.com/ClangBuiltLinux/linux/issues/1408 Signed-off-by: Nathan Chancellor <nathan@kernel.org> --- sound/usb/mixer_scarlett_gen2.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c index fcba682cd422..c20c7f1ddc50 100644 --- a/sound/usb/mixer_scarlett_gen2.c +++ b/sound/usb/mixer_scarlett_gen2.c @@ -1186,7 +1186,7 @@ static int scarlett2_usb_get_config( if (err < 0) return err; if (size == 2) - for (i = 0; i < count; i++, (u16 *)buf++) + for (i = 0; i < count; i++, buf = (u16 *)buf + 1) *(u16 *)buf = le16_to_cpu(*(__le16 *)buf); return 0; } base-commit: 5c89c2c7fbfa9124dd521c375b9c82b9ed75bc28 -- 2.32.0.93.g670b81a890
On Thu, Jun 24, 2021 at 02:20:48PM -0700, Nathan Chancellor wrote: > Clang warns: > > sound/usb/mixer_scarlett_gen2.c:1189:32: warning: expression result > unused [-Wunused-value] > for (i = 0; i < count; i++, (u16 *)buf++) > ^ ~~~~~ > 1 warning generated. > > It appears the intention was to cast the void pointer to a u16 pointer > so that the data could be iterated through like an array of u16 values. > However, the cast happens after the increment because a cast is an > rvalue, whereas the post-increment operator only works on lvalues, so > the loop does not iterate as expected. > > Replace the post-increment shorthand with the full expression so the > cast can be added in the right place and the look works as expected. look -> loop > Fixes: ac34df733d2d ("ALSA: usb-audio: scarlett2: Update get_config to do endian conversion") > Link: https://github.com/ClangBuiltLinux/linux/issues/1408 > Signed-off-by: Nathan Chancellor <nathan@kernel.org> > --- > sound/usb/mixer_scarlett_gen2.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c > index fcba682cd422..c20c7f1ddc50 100644 > --- a/sound/usb/mixer_scarlett_gen2.c > +++ b/sound/usb/mixer_scarlett_gen2.c > @@ -1186,7 +1186,7 @@ static int scarlett2_usb_get_config( > if (err < 0) > return err; > if (size == 2) > - for (i = 0; i < count; i++, (u16 *)buf++) > + for (i = 0; i < count; i++, buf = (u16 *)buf + 1) > *(u16 *)buf = le16_to_cpu(*(__le16 *)buf); > return 0; > } Thanks Nathan! FYI: although incorrect, this caused no bug as there is not yet any case where count > 1. Acked-by: Geoffrey D. Bennett <g@b4.vu>
On Thu, 24 Jun 2021 23:20:48 +0200,
Nathan Chancellor wrote:
>
> Clang warns:
>
> sound/usb/mixer_scarlett_gen2.c:1189:32: warning: expression result
> unused [-Wunused-value]
> for (i = 0; i < count; i++, (u16 *)buf++)
> ^ ~~~~~
> 1 warning generated.
>
> It appears the intention was to cast the void pointer to a u16 pointer
> so that the data could be iterated through like an array of u16 values.
> However, the cast happens after the increment because a cast is an
> rvalue, whereas the post-increment operator only works on lvalues, so
> the loop does not iterate as expected.
>
> Replace the post-increment shorthand with the full expression so the
> cast can be added in the right place and the look works as expected.
>
> Fixes: ac34df733d2d ("ALSA: usb-audio: scarlett2: Update get_config to do endian conversion")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1408
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
> sound/usb/mixer_scarlett_gen2.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c
> index fcba682cd422..c20c7f1ddc50 100644
> --- a/sound/usb/mixer_scarlett_gen2.c
> +++ b/sound/usb/mixer_scarlett_gen2.c
> @@ -1186,7 +1186,7 @@ static int scarlett2_usb_get_config(
> if (err < 0)
> return err;
> if (size == 2)
> - for (i = 0; i < count; i++, (u16 *)buf++)
> + for (i = 0; i < count; i++, buf = (u16 *)buf + 1)
> *(u16 *)buf = le16_to_cpu(*(__le16 *)buf);
That's still too error-prone.
Could you rather introduce another variable of u16 * type, and use it
instead? Ditto for u8 access for the code after that, too.
thanks,
Takashi
Clang warns: sound/usb/mixer_scarlett_gen2.c:1189:32: warning: expression result unused [-Wunused-value] for (i = 0; i < count; i++, (u16 *)buf++) ^ ~~~~~ 1 warning generated. It appears the intention was to cast the void pointer to a u16 pointer so that the data could be iterated through like an array of u16 values. However, the cast happens after the increment because a cast is an rvalue, whereas the post-increment operator only works on lvalues, so the loop does not iterate as expected. This is not a bug in practice because count is not greater than one at the moment but this could change in the future so this should be fixed. Replace the cast with a temporary variable of the proper type, which is less error prone and fixes the iteration. Do the same thing for the 'u8 *' below this if block. Fixes: ac34df733d2d ("ALSA: usb-audio: scarlett2: Update get_config to do endian conversion") Link: https://github.com/ClangBuiltLinux/linux/issues/1408 Signed-off-by: Nathan Chancellor <nathan@kernel.org> --- v1 -> v2: * Use temporary variables of proper type rather than casting, as requested by Takashi. I did not include Geoffrey's ack for this reason. * Mention that there is not a bug at the moment per Geoffrey's comment. sound/usb/mixer_scarlett_gen2.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c index fcba682cd422..b13903bed330 100644 --- a/sound/usb/mixer_scarlett_gen2.c +++ b/sound/usb/mixer_scarlett_gen2.c @@ -1177,17 +1177,22 @@ static int scarlett2_usb_get_config( const struct scarlett2_config *config_item = &scarlett2_config_items[info->has_mixer][config_item_num]; int size, err, i; + u8 *buf_8; u8 value; /* For byte-sized parameters, retrieve directly into buf */ if (config_item->size >= 8) { + u16 *buf_16; + size = config_item->size / 8 * count; err = scarlett2_usb_get(mixer, config_item->offset, buf, size); if (err < 0) return err; - if (size == 2) - for (i = 0; i < count; i++, (u16 *)buf++) - *(u16 *)buf = le16_to_cpu(*(__le16 *)buf); + if (size == 2) { + buf_16 = buf; + for (i = 0; i < count; i++, buf_16++) + *buf_16 = le16_to_cpu(*(__le16 *)buf_16); + } return 0; } @@ -1197,8 +1202,9 @@ static int scarlett2_usb_get_config( return err; /* then unpack from value into buf[] */ + buf_8 = buf; for (i = 0; i < 8 && i < count; i++, value >>= 1) - *(u8 *)buf++ = value & 1; + *buf_8++ = value & 1; return 0; } base-commit: 0cbbeaf370221fc469c95945dd3c1198865c5fe4 -- 2.32.0.93.g670b81a890
On Fri, Jun 25, 2021 at 10:54:19AM -0700, Nathan Chancellor wrote: > Clang warns: > > sound/usb/mixer_scarlett_gen2.c:1189:32: warning: expression result > unused [-Wunused-value] > for (i = 0; i < count; i++, (u16 *)buf++) > ^ ~~~~~ > 1 warning generated. > > It appears the intention was to cast the void pointer to a u16 pointer > so that the data could be iterated through like an array of u16 values. > However, the cast happens after the increment because a cast is an > rvalue, whereas the post-increment operator only works on lvalues, so > the loop does not iterate as expected. This is not a bug in practice > because count is not greater than one at the moment but this could > change in the future so this should be fixed. > > Replace the cast with a temporary variable of the proper type, which is > less error prone and fixes the iteration. Do the same thing for the > 'u8 *' below this if block. > > Fixes: ac34df733d2d ("ALSA: usb-audio: scarlett2: Update get_config to do endian conversion") > Link: https://github.com/ClangBuiltLinux/linux/issues/1408 > Signed-off-by: Nathan Chancellor <nathan@kernel.org> > --- > > v1 -> v2: > > * Use temporary variables of proper type rather than casting, as > requested by Takashi. I did not include Geoffrey's ack for this > reason. > > * Mention that there is not a bug at the moment per Geoffrey's comment. > > sound/usb/mixer_scarlett_gen2.c | 14 ++++++++++---- > 1 file changed, 10 insertions(+), 4 deletions(-) > > diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c > index fcba682cd422..b13903bed330 100644 > --- a/sound/usb/mixer_scarlett_gen2.c > +++ b/sound/usb/mixer_scarlett_gen2.c > @@ -1177,17 +1177,22 @@ static int scarlett2_usb_get_config( > const struct scarlett2_config *config_item = > &scarlett2_config_items[info->has_mixer][config_item_num]; > int size, err, i; > + u8 *buf_8; > u8 value; > > /* For byte-sized parameters, retrieve directly into buf */ > if (config_item->size >= 8) { > + u16 *buf_16; > + I would prefer that the u16 *buf_16 declaration above be removed from there... > size = config_item->size / 8 * count; > err = scarlett2_usb_get(mixer, config_item->offset, buf, size); > if (err < 0) > return err; > - if (size == 2) > - for (i = 0; i < count; i++, (u16 *)buf++) > - *(u16 *)buf = le16_to_cpu(*(__le16 *)buf); > + if (size == 2) { > + buf_16 = buf; ...and combined with the assignment here, like: u16 *buf_16 = buf; Regardless: Acked-by: Geoffrey D. Bennett <g@b4.vu> And, thanks again! > + for (i = 0; i < count; i++, buf_16++) > + *buf_16 = le16_to_cpu(*(__le16 *)buf_16); > + } > return 0; > } > > @@ -1197,8 +1202,9 @@ static int scarlett2_usb_get_config( > return err; > > /* then unpack from value into buf[] */ > + buf_8 = buf; > for (i = 0; i < 8 && i < count; i++, value >>= 1) > - *(u8 *)buf++ = value & 1; > + *buf_8++ = value & 1; > > return 0; > } > > base-commit: 0cbbeaf370221fc469c95945dd3c1198865c5fe4 > -- > 2.32.0.93.g670b81a890 >
Clang warns: sound/usb/mixer_scarlett_gen2.c:1189:32: warning: expression result unused [-Wunused-value] for (i = 0; i < count; i++, (u16 *)buf++) ^ ~~~~~ 1 warning generated. It appears the intention was to cast the void pointer to a u16 pointer so that the data could be iterated through like an array of u16 values. However, the cast happens after the increment because a cast is an rvalue, whereas the post-increment operator only works on lvalues, so the loop does not iterate as expected. Replace the cast with a temporary variable of the proper type, which is less error prone and fixes the iteration. Do the same thing for the 'u8 *' below this if block. Fixes: ac34df733d2d ("ALSA: usb-audio: scarlett2: Update get_config to do endian conversion") Link: https://github.com/ClangBuiltLinux/linux/issues/1408 Acked-by: Geoffrey D. Bennett <g@b4.vu> Signed-off-by: Nathan Chancellor <nathan@kernel.org> --- v1 -> v2: * Use temporary variables of proper type rather than casting, as requested by Takashi. * Mention that there is not a bug at the moment per Geoffrey's comment. v2 -> v3: * Restrict scope of buf_16 more, as requested by Geoffrey. * Add Geoffrey's ack. sound/usb/mixer_scarlett_gen2.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c index fcba682cd422..07ba0ef884a2 100644 --- a/sound/usb/mixer_scarlett_gen2.c +++ b/sound/usb/mixer_scarlett_gen2.c @@ -1177,17 +1177,22 @@ static int scarlett2_usb_get_config( const struct scarlett2_config *config_item = &scarlett2_config_items[info->has_mixer][config_item_num]; int size, err, i; + u8 *buf_8; u8 value; /* For byte-sized parameters, retrieve directly into buf */ if (config_item->size >= 8) { + size = config_item->size / 8 * count; err = scarlett2_usb_get(mixer, config_item->offset, buf, size); if (err < 0) return err; - if (size == 2) - for (i = 0; i < count; i++, (u16 *)buf++) - *(u16 *)buf = le16_to_cpu(*(__le16 *)buf); + if (size == 2) { + u16 *buf_16 = buf; + + for (i = 0; i < count; i++, buf_16++) + *buf_16 = le16_to_cpu(*(__le16 *)buf_16); + } return 0; } @@ -1197,8 +1202,9 @@ static int scarlett2_usb_get_config( return err; /* then unpack from value into buf[] */ + buf_8 = buf; for (i = 0; i < 8 && i < count; i++, value >>= 1) - *(u8 *)buf++ = value & 1; + *buf_8++ = value & 1; return 0; } base-commit: 0cbbeaf370221fc469c95945dd3c1198865c5fe4 -- 2.32.0.93.g670b81a890
On Sat, Jun 26, 2021 at 04:13:42AM +0930, Geoffrey D. Bennett wrote: > On Fri, Jun 25, 2021 at 10:54:19AM -0700, Nathan Chancellor wrote: > > Clang warns: > > > > sound/usb/mixer_scarlett_gen2.c:1189:32: warning: expression result > > unused [-Wunused-value] > > for (i = 0; i < count; i++, (u16 *)buf++) > > ^ ~~~~~ > > 1 warning generated. > > > > It appears the intention was to cast the void pointer to a u16 pointer > > so that the data could be iterated through like an array of u16 values. > > However, the cast happens after the increment because a cast is an > > rvalue, whereas the post-increment operator only works on lvalues, so > > the loop does not iterate as expected. This is not a bug in practice > > because count is not greater than one at the moment but this could > > change in the future so this should be fixed. > > > > Replace the cast with a temporary variable of the proper type, which is > > less error prone and fixes the iteration. Do the same thing for the > > 'u8 *' below this if block. > > > > Fixes: ac34df733d2d ("ALSA: usb-audio: scarlett2: Update get_config to do endian conversion") > > Link: https://github.com/ClangBuiltLinux/linux/issues/1408 > > Signed-off-by: Nathan Chancellor <nathan@kernel.org> > > --- > > > > v1 -> v2: > > > > * Use temporary variables of proper type rather than casting, as > > requested by Takashi. I did not include Geoffrey's ack for this > > reason. > > > > * Mention that there is not a bug at the moment per Geoffrey's comment. > > > > sound/usb/mixer_scarlett_gen2.c | 14 ++++++++++---- > > 1 file changed, 10 insertions(+), 4 deletions(-) > > > > diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c > > index fcba682cd422..b13903bed330 100644 > > --- a/sound/usb/mixer_scarlett_gen2.c > > +++ b/sound/usb/mixer_scarlett_gen2.c > > @@ -1177,17 +1177,22 @@ static int scarlett2_usb_get_config( > > const struct scarlett2_config *config_item = > > &scarlett2_config_items[info->has_mixer][config_item_num]; > > int size, err, i; > > + u8 *buf_8; > > u8 value; > > > > /* For byte-sized parameters, retrieve directly into buf */ > > if (config_item->size >= 8) { > > + u16 *buf_16; > > + > > I would prefer that the u16 *buf_16 declaration above be removed from > there... > > > size = config_item->size / 8 * count; > > err = scarlett2_usb_get(mixer, config_item->offset, buf, size); > > if (err < 0) > > return err; > > - if (size == 2) > > - for (i = 0; i < count; i++, (u16 *)buf++) > > - *(u16 *)buf = le16_to_cpu(*(__le16 *)buf); > > + if (size == 2) { > > + buf_16 = buf; > > ...and combined with the assignment here, like: u16 *buf_16 = buf; Thanks for pointing it out, I was not paying enough attention to realize that the scope could be reduced. v3 sent with your Ack added, thank you for taking a look in a quick manner! Cheers, Nathan > Regardless: > > Acked-by: Geoffrey D. Bennett <g@b4.vu> > > And, thanks again! > > > + for (i = 0; i < count; i++, buf_16++) > > + *buf_16 = le16_to_cpu(*(__le16 *)buf_16); > > + } > > return 0; > > } > > > > @@ -1197,8 +1202,9 @@ static int scarlett2_usb_get_config( > > return err; > > > > /* then unpack from value into buf[] */ > > + buf_8 = buf; > > for (i = 0; i < 8 && i < count; i++, value >>= 1) > > - *(u8 *)buf++ = value & 1; > > + *buf_8++ = value & 1; > > > > return 0; > > } > > > > base-commit: 0cbbeaf370221fc469c95945dd3c1198865c5fe4 > > -- > > 2.32.0.93.g670b81a890 > >
Clang warns: sound/usb/mixer_scarlett_gen2.c:1189:32: warning: expression result unused [-Wunused-value] for (i = 0; i < count; i++, (u16 *)buf++) ^ ~~~~~ 1 warning generated. It appears the intention was to cast the void pointer to a u16 pointer so that the data could be iterated through like an array of u16 values. However, the cast happens after the increment because a cast is an rvalue, whereas the post-increment operator only works on lvalues, so the loop does not iterate as expected. Replace the cast with a temporary variable of the proper type, which is less error prone and fixes the iteration. Do the same thing for the 'u8 *' below this if block. Fixes: ac34df733d2d ("ALSA: usb-audio: scarlett2: Update get_config to do endian conversion") Link: https://github.com/ClangBuiltLinux/linux/issues/1408 Acked-by: Geoffrey D. Bennett <g@b4.vu> Signed-off-by: Nathan Chancellor <nathan@kernel.org> --- v1 -> v2: * Use temporary variables of proper type rather than casting, as requested by Takashi. * Mention that there is not a bug at the moment per Geoffrey's comment. v2 -> v3: * Restrict scope of buf_16 more, as requested by Geoffrey. * Add Geoffrey's ack. v3 -> v4: * Fix stray newline added below if (config_item->size >= 8) { leftover from buf_16's declaration. sound/usb/mixer_scarlett_gen2.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c index fcba682cd422..161d832cafef 100644 --- a/sound/usb/mixer_scarlett_gen2.c +++ b/sound/usb/mixer_scarlett_gen2.c @@ -1177,6 +1177,7 @@ static int scarlett2_usb_get_config( const struct scarlett2_config *config_item = &scarlett2_config_items[info->has_mixer][config_item_num]; int size, err, i; + u8 *buf_8; u8 value; /* For byte-sized parameters, retrieve directly into buf */ @@ -1185,9 +1186,12 @@ static int scarlett2_usb_get_config( err = scarlett2_usb_get(mixer, config_item->offset, buf, size); if (err < 0) return err; - if (size == 2) - for (i = 0; i < count; i++, (u16 *)buf++) - *(u16 *)buf = le16_to_cpu(*(__le16 *)buf); + if (size == 2) { + u16 *buf_16 = buf; + + for (i = 0; i < count; i++, buf_16++) + *buf_16 = le16_to_cpu(*(__le16 *)buf_16); + } return 0; } @@ -1197,8 +1201,9 @@ static int scarlett2_usb_get_config( return err; /* then unpack from value into buf[] */ + buf_8 = buf; for (i = 0; i < 8 && i < count; i++, value >>= 1) - *(u8 *)buf++ = value & 1; + *buf_8++ = value & 1; return 0; } base-commit: 0cbbeaf370221fc469c95945dd3c1198865c5fe4 -- 2.32.0.93.g670b81a890
On Fri, Jun 25, 2021 at 01:11:51PM -0700, Nathan Chancellor wrote: > Clang warns: > > sound/usb/mixer_scarlett_gen2.c:1189:32: warning: expression result > unused [-Wunused-value] > for (i = 0; i < count; i++, (u16 *)buf++) > ^ ~~~~~ > 1 warning generated. > > It appears the intention was to cast the void pointer to a u16 pointer > so that the data could be iterated through like an array of u16 values. > However, the cast happens after the increment because a cast is an > rvalue, whereas the post-increment operator only works on lvalues, so > the loop does not iterate as expected. Your note about no bug which was added in v2 went missing in v3: > > the loop does not iterate as expected. This is not a bug in practice > > because count is not greater than one at the moment but this could > > change in the future so this should be fixed. > Replace the cast with a temporary variable of the proper type, which is > less error prone and fixes the iteration. Do the same thing for the > 'u8 *' below this if block. > > Fixes: ac34df733d2d ("ALSA: usb-audio: scarlett2: Update get_config to do endian conversion") > Link: https://github.com/ClangBuiltLinux/linux/issues/1408 > Acked-by: Geoffrey D. Bennett <g@b4.vu> > Signed-off-by: Nathan Chancellor <nathan@kernel.org> > --- > > v1 -> v2: > > * Use temporary variables of proper type rather than casting, as > requested by Takashi. > > * Mention that there is not a bug at the moment per Geoffrey's comment. > > v2 -> v3: > > * Restrict scope of buf_16 more, as requested by Geoffrey. > > * Add Geoffrey's ack. > > v3 -> v4: > > * Fix stray newline added below > > if (config_item->size >= 8) { > > leftover from buf_16's declaration. > > sound/usb/mixer_scarlett_gen2.c | 13 +++++++++---- > 1 file changed, 9 insertions(+), 4 deletions(-) > > diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c > index fcba682cd422..161d832cafef 100644 > --- a/sound/usb/mixer_scarlett_gen2.c > +++ b/sound/usb/mixer_scarlett_gen2.c > @@ -1177,6 +1177,7 @@ static int scarlett2_usb_get_config( > const struct scarlett2_config *config_item = > &scarlett2_config_items[info->has_mixer][config_item_num]; > int size, err, i; > + u8 *buf_8; > u8 value; > > /* For byte-sized parameters, retrieve directly into buf */ > @@ -1185,9 +1186,12 @@ static int scarlett2_usb_get_config( > err = scarlett2_usb_get(mixer, config_item->offset, buf, size); > if (err < 0) > return err; > - if (size == 2) > - for (i = 0; i < count; i++, (u16 *)buf++) > - *(u16 *)buf = le16_to_cpu(*(__le16 *)buf); > + if (size == 2) { > + u16 *buf_16 = buf; > + > + for (i = 0; i < count; i++, buf_16++) > + *buf_16 = le16_to_cpu(*(__le16 *)buf_16); > + } > return 0; > } > > @@ -1197,8 +1201,9 @@ static int scarlett2_usb_get_config( > return err; > > /* then unpack from value into buf[] */ > + buf_8 = buf; > for (i = 0; i < 8 && i < count; i++, value >>= 1) > - *(u8 *)buf++ = value & 1; > + *buf_8++ = value & 1; > > return 0; > } > > base-commit: 0cbbeaf370221fc469c95945dd3c1198865c5fe4 > -- > 2.32.0.93.g670b81a890 >
Clang warns: sound/usb/mixer_scarlett_gen2.c:1189:32: warning: expression result unused [-Wunused-value] for (i = 0; i < count; i++, (u16 *)buf++) ^ ~~~~~ 1 warning generated. It appears the intention was to cast the void pointer to a u16 pointer so that the data could be iterated through like an array of u16 values. However, the cast happens after the increment because a cast is an rvalue, whereas the post-increment operator only works on lvalues, so the loop does not iterate as expected. This is not a bug in practice because count is not greater than one at the moment but this could change in the future so this should be fixed. Replace the cast with a temporary variable of the proper type, which is less error prone and fixes the iteration. Do the same thing for the 'u8 *' below this if block. Fixes: ac34df733d2d ("ALSA: usb-audio: scarlett2: Update get_config to do endian conversion") Link: https://github.com/ClangBuiltLinux/linux/issues/1408 Acked-by: Geoffrey D. Bennett <g@b4.vu> Signed-off-by: Nathan Chancellor <nathan@kernel.org> --- v1 -> v2: * Use temporary variables of proper type rather than casting, as requested by Takashi. * Mention that there is not a bug at the moment per Geoffrey's comment. v2 -> v3: * Restrict scope of buf_16 more, as requested by Geoffrey. * Add Geoffrey's ack. v3 -> v4: * Fix stray newline added below if (config_item->size >= 8) { leftover from buf_16's declaration. v4 -> v5 (or how many times does it take Nathan to get a patch right): * Re-add note about no bug that was dropped in v3 by accident, as noticed by Geoffrey. My apologies for the multiple revisions. sound/usb/mixer_scarlett_gen2.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c index fcba682cd422..161d832cafef 100644 --- a/sound/usb/mixer_scarlett_gen2.c +++ b/sound/usb/mixer_scarlett_gen2.c @@ -1177,6 +1177,7 @@ static int scarlett2_usb_get_config( const struct scarlett2_config *config_item = &scarlett2_config_items[info->has_mixer][config_item_num]; int size, err, i; + u8 *buf_8; u8 value; /* For byte-sized parameters, retrieve directly into buf */ @@ -1185,9 +1186,12 @@ static int scarlett2_usb_get_config( err = scarlett2_usb_get(mixer, config_item->offset, buf, size); if (err < 0) return err; - if (size == 2) - for (i = 0; i < count; i++, (u16 *)buf++) - *(u16 *)buf = le16_to_cpu(*(__le16 *)buf); + if (size == 2) { + u16 *buf_16 = buf; + + for (i = 0; i < count; i++, buf_16++) + *buf_16 = le16_to_cpu(*(__le16 *)buf_16); + } return 0; } @@ -1197,8 +1201,9 @@ static int scarlett2_usb_get_config( return err; /* then unpack from value into buf[] */ + buf_8 = buf; for (i = 0; i < 8 && i < count; i++, value >>= 1) - *(u8 *)buf++ = value & 1; + *buf_8++ = value & 1; return 0; } base-commit: 0cbbeaf370221fc469c95945dd3c1198865c5fe4 -- 2.32.0.93.g670b81a890
On Sun, 27 Jun 2021 07:12:03 +0200,
Nathan Chancellor wrote:
>
> Clang warns:
>
> sound/usb/mixer_scarlett_gen2.c:1189:32: warning: expression result
> unused [-Wunused-value]
> for (i = 0; i < count; i++, (u16 *)buf++)
> ^ ~~~~~
> 1 warning generated.
>
> It appears the intention was to cast the void pointer to a u16 pointer
> so that the data could be iterated through like an array of u16 values.
> However, the cast happens after the increment because a cast is an
> rvalue, whereas the post-increment operator only works on lvalues, so
> the loop does not iterate as expected. This is not a bug in practice
> because count is not greater than one at the moment but this could
> change in the future so this should be fixed.
>
> Replace the cast with a temporary variable of the proper type, which is
> less error prone and fixes the iteration. Do the same thing for the
> 'u8 *' below this if block.
>
> Fixes: ac34df733d2d ("ALSA: usb-audio: scarlett2: Update get_config to do endian conversion")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1408
> Acked-by: Geoffrey D. Bennett <g@b4.vu>
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
>
> v1 -> v2:
>
> * Use temporary variables of proper type rather than casting, as
> requested by Takashi.
>
> * Mention that there is not a bug at the moment per Geoffrey's comment.
>
> v2 -> v3:
>
> * Restrict scope of buf_16 more, as requested by Geoffrey.
>
> * Add Geoffrey's ack.
>
> v3 -> v4:
>
> * Fix stray newline added below
>
> if (config_item->size >= 8) {
>
> leftover from buf_16's declaration.
>
> v4 -> v5 (or how many times does it take Nathan to get a patch right):
>
> * Re-add note about no bug that was dropped in v3 by accident, as
> noticed by Geoffrey. My apologies for the multiple revisions.
Thanks, applied now.
Takashi