From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <nightstrike@gmail.com>
Received: from mail-io1-xd35.google.com (mail-io1-xd35.google.com
 [IPv6:2607:f8b0:4864:20::d35])
 by sourceware.org (Postfix) with ESMTPS id BD634385DC00
 for <gcc-help@gcc.gnu.org>; Sun, 31 May 2020 18:32:44 +0000 (GMT)
DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org BD634385DC00
Received: by mail-io1-xd35.google.com with SMTP id h4so1408260iob.10
 for <gcc-help@gcc.gnu.org>; Sun, 31 May 2020 11:32:44 -0700 (PDT)
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
 d=1e100.net; s=20161025;
 h=x-gm-message-state:mime-version:from:date:message-id:subject:to;
 bh=B5iTgy3OCSyFzYV0x/elrStCOlGM6HNgFjigTmQy8io=;
 b=TBixorK+1bM0diOvfwrlmDVN0a6gSeVExxPofUuZ7KDDLO+/yl8xkU/IESAlauHg0y
 +4+wtO7i7al2ViJUXhkgjthYPKt1zS5LSvoZi9BY3+s2zybQxADfnJyCipu7WgYd/yX5
 pASIAxtnhyH+k72pzG/GaMJc8Vg3A4ibX6TH6yLXAOrRvxK0qCjZHw5eZnLiYo0hgoKK
 QyyXAzEanbEQPQpTqCbPHf3tftnU5esIpTVeOKQZVHNpG7PXwoAMLLTwcw4fYIKdHa/o
 Bf6zGBHLJvp4ieQYX7A9bdtWEGVzY7eJ7gWaxitRc+fdfZzix2meuIJpZ4GnlnfiAQ27
 7HkQ==
X-Gm-Message-State: AOAM531WkaQ7ACQT0K67CHSmLcqqt8yftBUC8P4bN90t/QgFanVKUK0O
 gObm98zv5SJZgDD9RBF++lAhihscvDxYqRafx91UMCX2
X-Google-Smtp-Source: ABdhPJxVc9b9wLCr2X0jE4xoZjcWyejF+nMGaMPdmIiMghX7JXMPVbzX++TsLL5Guke03tFUVHQ1qYZyxHnf/cPdPsw=
X-Received: by 2002:a5e:8e47:: with SMTP id r7mr15787101ioo.204.1590949963942; 
 Sun, 31 May 2020 11:32:43 -0700 (PDT)
MIME-Version: 1.0
From: NightStrike <nightstrike@gmail.com>
Date: Sun, 31 May 2020 14:32:33 -0400
Message-ID: <CAF1jjLtT6FezTsdZ5EU0+eH5pyR9m1zWT6-Ebv91PvxX-0tw-A@mail.gmail.com>
Subject: Strange warning on printf checks
To: gcc-help <gcc-help@gcc.gnu.org>
X-Spam-Status: No, score=-3.1 required=5.0 tests=BAYES_00, DKIM_SIGNED,
 DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, HTML_MESSAGE,
 RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS,
 TXREP autolearn=ham autolearn_force=no version=3.4.2
X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on
 server2.sourceware.org
Content-Type: text/plain; charset="UTF-8"
X-Content-Filtered-By: Mailman/MimeDel 2.1.29
X-BeenThere: gcc-help@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-help mailing list <gcc-help.gcc.gnu.org>
List-Unsubscribe: <http://gcc.gnu.org/mailman/options/gcc-help>,
 <mailto:gcc-help-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-help/>
List-Post: <mailto:gcc-help@gcc.gnu.org>
List-Help: <mailto:gcc-help-request@gcc.gnu.org?subject=help>
List-Subscribe: <http://gcc.gnu.org/mailman/listinfo/gcc-help>,
 <mailto:gcc-help-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Sun, 31 May 2020 18:32:45 -0000

I'm curious if this is a gcc bug or not.  The warning I get is trying to
highlight a real problem, but it's referring to a string literal as a
directive, which I thought was just for the %XX printf commands.  Given the
following:

#include <stdio.h>

void f() {
    char x[4];
    char y[5];
    sprintf(x, "%s_%s", y, y);
}

$ gcc a.c -c -Wall
a.c: In function 'f':
a.c:6:16: warning: '_' directive writing 1 byte into a region of size
between 0 and 4 [-Wformat-overflow=]
    6 |  sprintf(x, "%s_%s", y, y);
      |                ^
a.c:6:2: note: 'sprintf' output between 2 and 10 bytes into a destination
of size 4
    6 |  sprintf(x, "%s_%s", y, y);
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~


I hope the fixed width display shows this correctly.  The point is that the
^ points to the underscore, which is right, but the message calls the
underscore a printf directive.

Maybe I'm splitting hairs, but this confused me for a good half hour before
I realized what was wrong.