From: Larry Finger Date: Thu, 19 May 2011 17:12:25 -0500 Subject: [PATCH] b43: Fix bogus compilation warning for phy_n In-Reply-To: References: <4dd58d39.ev8WALmbdvCfJmAJ%Larry.Finger@lwfinger.net> Message-ID: <4DD595C9.105@lwfinger.net> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= Cc: John W Linville , b43-dev@lists.infradead.org, linux-wireless@vger.kernel.org On 05/19/2011 04:43 PM, Rafa? Mi?ecki wrote: > 2011/5/19 Larry Finger: >> When cross-compiling the 2.6.39 wireless-testing source using GCC version >> (SUSE Linux) 4.3.2 [gcc-4_3-branch revision 141291] on an x86_64 system, >> the following warning is issued: >> >> CC [M] drivers/net/wireless/b43/phy_n.o >> drivers/net/wireless/b43/phy_n.c: In function ?b43_nphy_cal_tx_iq_lo?: >> drivers/net/wireless/b43/phy_n.c:3096: warning: ?last? may be used >> uninitialized in this function >> >> A quick look at the code shows that the warning is bogus and a gcc bug, >> but to ensure clean compilation for all users, mark the offending variable >> as uninitialized. > > Did you check for both "last" usages on this function? From my quick > review it seems "last" is set in case of > 1) mphase_cal_phase_id> 2 > xor > 2) b43_nphy_tx_tone returning success > > I'm not so sure if this patch is correct. My analysis is as follows: "last" is created in line 3096. In line 3256, it is set by the statement "last = (dev->phy.rev < 3) ? 6 : 7;". In line 3258 and 3300, it is tested for equality with "nphy->mphase_cal_phase_id". As there is no path around line 3256, it seems to me that last must be assigned a value at 3256 and the warning is bogus. The call in line 3154 to b43_nphy_tx_tone is "error = b43_nphy_tx_tone(dev, freq, 250, true, false);" and does not access last. If this patch is not correct, then last must be initialized to zero and the older compiler is correct and the newer ones are buggy for not reporting the problem. Larry