| Message ID | 20210625175418.2019892-1-nathan@kernel.org (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v2] ALSA: usb-audio: scarlett2: Fix for loop increment in scarlett2_usb_get_config | expand |
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 >
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 > >
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; }
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(-) base-commit: 0cbbeaf370221fc469c95945dd3c1198865c5fe4