From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH] Input: tca8418_keypad: hide gcc-4.9 -Wmaybe-uninitialized warning Date: Tue, 25 Oct 2016 11:59:22 +0200 Message-ID: <3580924.2eqYJQ5Dgh@wuerfel> References: <20161024153222.2738294-1-arnd@arndb.de> <20161024234513.GA15034@dtor-ws> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: Received: from mout.kundenserver.de ([212.227.126.135]:61328 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933920AbcJYJ70 (ORCPT ); Tue, 25 Oct 2016 05:59:26 -0400 In-Reply-To: <20161024234513.GA15034@dtor-ws> Sender: linux-input-owner@vger.kernel.org List-Id: linux-input@vger.kernel.org To: Dmitry Torokhov Cc: linux-input@vger.kernel.org, linux-kernel@vger.kernel.org On Monday, October 24, 2016 4:45:13 PM CEST Dmitry Torokhov wrote: > > diff --git a/drivers/input/keyboard/tca8418_keypad.c b/drivers/input/keyboard/tca8418_keypad.c > > index 9002298698fc..3048ef3e3e16 100644 > > --- a/drivers/input/keyboard/tca8418_keypad.c > > +++ b/drivers/input/keyboard/tca8418_keypad.c > > @@ -164,11 +164,18 @@ static void tca8418_read_keypad(struct tca8418_keypad *keypad_data) > > int error, col, row; > > u8 reg, state, code; > > > > - /* Initial read of the key event FIFO */ > > - error = tca8418_read_byte(keypad_data, REG_KEY_EVENT_A, ®); > > + do { > > + error = tca8418_read_byte(keypad_data, REG_KEY_EVENT_A, ®); > > + if (error < 0) { > > + dev_err(&keypad_data->client->dev, > > + "unable to read REG_KEY_EVENT_A\n"); > > + break; > > + } > > + > > + /* Assume that key code 0 signifies empty FIFO */ > > + if (reg <= 0) > > + break; > > I am unconvinced that this rearrangement fixes the issue for all older > GCCs. Can we simply do: > > u8 uninitialized_var(reg); > > and be done with it? Yes, that would work. However: - avoiding the fake intialization tends to produce better object code, as gcc actually knows what's going on - Linus doesn't like uninitialized_var() and would rather see it removed from the kernel - llvm produces warnings for uninitialized_var() I have checked gcc-4.6/4.7/4.8/4.9/5.x/6.x, and only gcc-4.9 produces the warning. 4.9 changed the detection for uninitialized variables significantly, which generally caused fewer false positives but unfortunately introduced a couple of new ones like this. Arnd