From: "Geoffrey D. Bennett" <g@b4.vu> To: Nathan Chancellor <nathan@kernel.org> Cc: Jaroslav Kysela <perex@perex.cz>, Takashi Iwai <tiwai@suse.com>, Nick Desaulniers <ndesaulniers@google.com>, alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com Subject: Re: [PATCH] ALSA: usb-audio: scarlett2: Fix for loop increment in scarlett2_usb_get_config Date: Fri, 25 Jun 2021 11:37:48 +0930 [thread overview] Message-ID: <20210625020748.GA21766@m.b4.vu> (raw) In-Reply-To: <20210624212048.1356136-1-nathan@kernel.org> 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>
WARNING: multiple messages have this Message-ID (diff)
From: "Geoffrey D. Bennett" <g@b4.vu> To: Nathan Chancellor <nathan@kernel.org> Cc: alsa-devel@alsa-project.org, Nick Desaulniers <ndesaulniers@google.com>, linux-kernel@vger.kernel.org, Takashi Iwai <tiwai@suse.com>, clang-built-linux@googlegroups.com Subject: Re: [PATCH] ALSA: usb-audio: scarlett2: Fix for loop increment in scarlett2_usb_get_config Date: Fri, 25 Jun 2021 11:37:48 +0930 [thread overview] Message-ID: <20210625020748.GA21766@m.b4.vu> (raw) In-Reply-To: <20210624212048.1356136-1-nathan@kernel.org> 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>
next prev parent reply other threads:[~2021-06-25 2:14 UTC|newest] Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-06-24 21:20 [PATCH] ALSA: usb-audio: scarlett2: Fix for loop increment in scarlett2_usb_get_config Nathan Chancellor 2021-06-24 21:20 ` Nathan Chancellor 2021-06-25 2:07 ` Geoffrey D. Bennett [this message] 2021-06-25 2:07 ` Geoffrey D. Bennett 2021-06-25 7:45 ` Takashi Iwai 2021-06-25 7:45 ` Takashi Iwai 2021-06-25 17:54 ` [PATCH v2] " Nathan Chancellor 2021-06-25 17:54 ` Nathan Chancellor 2021-06-25 18:43 ` Geoffrey D. Bennett 2021-06-25 18:43 ` Geoffrey D. Bennett 2021-06-25 20:05 ` [PATCH v3] " Nathan Chancellor 2021-06-25 20:05 ` Nathan Chancellor 2021-06-25 20:11 ` [PATCH v4] " Nathan Chancellor 2021-06-25 20:11 ` Nathan Chancellor 2021-06-25 20:26 ` Geoffrey D. Bennett 2021-06-25 20:26 ` Geoffrey D. Bennett 2021-06-27 5:12 ` [PATCH v5] " Nathan Chancellor 2021-06-27 5:12 ` Nathan Chancellor 2021-07-01 17:12 ` Takashi Iwai 2021-07-01 17:12 ` Takashi Iwai 2021-06-25 20:08 ` [PATCH v2] " Nathan Chancellor 2021-06-25 20:08 ` Nathan Chancellor
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