| Message ID | 20210627051202.1888250-1-nathan@kernel.org (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 9a7b7ec3c6f2aedb99c9f39dd9cb63c2deff3437 |
| Headers | show |
| Series | [v5] ALSA: usb-audio: scarlett2: Fix for loop increment in scarlett2_usb_get_config | expand |
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
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; }
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(-) base-commit: 0cbbeaf370221fc469c95945dd3c1198865c5fe4