From: Arnd Bergmann <arnd@arndb.de> To: Sergey Kozlov <serjk@netup.ru>, Abylay Ospan <aospan@netup.ru>, Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Jason Baron <jbaron@akamai.com>, Arnd Bergmann <arnd@arndb.de>, linux-media@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] [media] cxd2841er: avoid misleading gcc warning Date: Wed, 13 Jul 2016 22:42:33 +0200 Message-ID: <20160713204342.1221511-1-arnd@arndb.de> (raw) The addition of jump label support in dynamic_debug caused an unexpected warning in exactly one file in the kernel: drivers/media/dvb-frontends/cxd2841er.c: In function 'cxd2841er_tune_tc': include/linux/dynamic_debug.h:134:3: error: 'carrier_offset' may be used uninitialized in this function [-Werror=maybe-uninitialized] __dynamic_dev_dbg(&descriptor, dev, fmt, \ ^~~~~~~~~~~~~~~~~ drivers/media/dvb-frontends/cxd2841er.c:3177:11: note: 'carrier_offset' was declared here int ret, carrier_offset; ^~~~~~~~~~~~~~ The problem seems to be that the compiler gets confused by the extra conditionals in static_branch_unlikely, to the point where it can no longer keep track of which branches have already been taken, and it doesn't realize that this variable is now always initialized when it gets used. I have done lots of randconfig kernel builds and could not find any other file with this behavior, so I assume it's a rare enough glitch that we don't need to change the jump label support but instead just work around the warning in the driver. To achieve that, I'm moving the check for the return value into the switch() statement, which is an obvious transformation, but is enough to un-confuse the compiler here. The resulting code is not as nice to read, but at least we retain the behavior of warning if it gets changed to actually access an uninitialized carrier offset value in the future. Signed-off-by: Arnd Bergmann <arnd@arndb.de> Fixes: (in linux-mm) "dynamic_debug: add jump label support" --- drivers/media/dvb-frontends/cxd2841er.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/drivers/media/dvb-frontends/cxd2841er.c b/drivers/media/dvb-frontends/cxd2841er.c index 721fb074da7c..0639ca281a2c 100644 --- a/drivers/media/dvb-frontends/cxd2841er.c +++ b/drivers/media/dvb-frontends/cxd2841er.c @@ -3223,20 +3223,28 @@ static int cxd2841er_tune_tc(struct dvb_frontend *fe, ret = cxd2841er_get_carrier_offset_i( priv, p->bandwidth_hz, &carrier_offset); + if (ret) + return ret; break; case SYS_DVBT: ret = cxd2841er_get_carrier_offset_t( priv, p->bandwidth_hz, &carrier_offset); + if (ret) + return ret; break; case SYS_DVBT2: ret = cxd2841er_get_carrier_offset_t2( priv, p->bandwidth_hz, &carrier_offset); + if (ret) + return ret; break; case SYS_DVBC_ANNEX_A: ret = cxd2841er_get_carrier_offset_c( priv, &carrier_offset); + if (ret) + return ret; break; default: dev_dbg(&priv->i2c->dev, @@ -3244,8 +3252,6 @@ static int cxd2841er_tune_tc(struct dvb_frontend *fe, __func__, priv->system); return -EINVAL; } - if (ret) - return ret; dev_dbg(&priv->i2c->dev, "%s(): carrier offset %d\n", __func__, carrier_offset); p->frequency += carrier_offset; -- 2.9.0
next reply index Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-07-13 20:42 Arnd Bergmann [this message] 2016-07-25 4:24 ` Abylay Ospan
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20160713204342.1221511-1-arnd@arndb.de \ --to=arnd@arndb.de \ --cc=aospan@netup.ru \ --cc=jbaron@akamai.com \ --cc=linux-kernel@vger.kernel.org \ --cc=linux-media@vger.kernel.org \ --cc=mchehab@kernel.org \ --cc=serjk@netup.ru \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
Linux-Media Archive on lore.kernel.org Archives are clonable: git clone --mirror https://lore.kernel.org/linux-media/0 linux-media/git/0.git # If you have public-inbox 1.1+ installed, you may # initialize and index your mirror using the following commands: public-inbox-init -V2 linux-media linux-media/ https://lore.kernel.org/linux-media \ linux-media@vger.kernel.org public-inbox-index linux-media Example config snippet for mirrors Newsgroup available over NNTP: nntp://nntp.lore.kernel.org/org.kernel.vger.linux-media AGPL code for this site: git clone https://public-inbox.org/public-inbox.git