| Message ID | 20210624212048.1356136-1-nathan@kernel.org (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | ALSA: usb-audio: scarlett2: Fix for loop increment in scarlett2_usb_get_config | expand |
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
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; }
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(-) base-commit: 5c89c2c7fbfa9124dd521c375b9c82b9ed75bc28