From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id 0E938385AC12 for ; Mon, 22 Aug 2022 02:39:54 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 0E938385AC12 Received: from mail-yw1-f198.google.com (mail-yw1-f198.google.com [209.85.128.198]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_128_GCM_SHA256) id us-mta-208-g3uB2g9QP_igZx6OCop5dQ-1; Sun, 21 Aug 2022 22:39:52 -0400 X-MC-Unique: g3uB2g9QP_igZx6OCop5dQ-1 Received: by mail-yw1-f198.google.com with SMTP id 00721157ae682-33580e26058so165680807b3.4 for ; Sun, 21 Aug 2022 19:39:52 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=to:subject:message-id:date:from:in-reply-to:references:mime-version :x-gm-message-state:from:to:cc; bh=jFc7Byx6zMU8D57atRq6Xcd6JVnQXIUimVzSlM9IqQ0=; b=Aa94VBI2nHdzoNRR46UHNZle9y0hAL/552YHZ2UQ0UC6fgjnW616tEohj6DYrokdne DUGECPZDBMe7/IB5plrNrmwIVtqq857t/SwOwsA84V7HyYjzJ8CYUz4+5QlbgrCmYUBe UXr6NQ0QtLirCSo1XFCJZKTKU/wvJ6IVHgDkx0fDSLgJwMRsIOAIeh7W2tielrCd0BOs pCyNMzZ0jM7d9JtiOCuXClwcgdpqSXUqa26LC1GqMJvOSBE4H/JXVIhxRDffvL/fZiRz 1XBdQANWHqTFaWrSAs2H7ICoYQGhlYHh+dASmRfKz7s4nWr94zXiMoZpRVV/BL6Nj8uC tBVg== X-Gm-Message-State: ACgBeo35z8Sr7XRiDhbGrB97y1/xmBE3oZ0S8Pu0C0tFs0avHBoyDG/t onIuAC4BOmswgcoR892rCLa+v6AtEYTt/i22RrQsaP9pHeg+yS+gMkXJQg0qX3vG3rW/HUzz77M Y/ObV0kIT37hNpAm2695BkiR5ic03hQ== X-Received: by 2002:a0d:cad1:0:b0:335:8273:e9fd with SMTP id m200-20020a0dcad1000000b003358273e9fdmr18624592ywd.154.1661135991727; Sun, 21 Aug 2022 19:39:51 -0700 (PDT) X-Google-Smtp-Source: AA6agR7H2BpEK1OM8WfnN+SxQ5EJria49Tz6cElquvrNAEsqnLWQC7uVdKvpg5GMNXCyA9nK3uVHHjRPQ12KxkgQz1k= X-Received: by 2002:a0d:cad1:0:b0:335:8273:e9fd with SMTP id m200-20020a0dcad1000000b003358273e9fdmr18624577ywd.154.1661135991443; Sun, 21 Aug 2022 19:39:51 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Reid Wahl Date: Sun, 21 Aug 2022 19:39:40 -0700 Message-ID: Subject: Re: -fno-builtin not preventing __builtin___snprintf_chk in gcc 11.2.0-19ubuntu1 To: gcc-help@gcc.gnu.org X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-3.0 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, KAM_NUMSUBJECT, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: gcc-help@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-help mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 22 Aug 2022 02:39:55 -0000 On Sun, Aug 21, 2022 at 5:53 PM Reid Wahl wrote: > > Hello, > > I'm hitting a strange issue with GCC while trying to wrap and mock > snprintf() for unit testing purposes. > > I'm setting -fno-builtin and -fno-inline, but > __builtin___snprintf_chk() is getting called instead of snprintf(). > The net effect is that my __wrap__snprintf() never gets called. Do you > have any advice on how to prevent object size checking builtins from > being used, without setting a lower optimization level? I expected > -fno-builtin to take care of it. > > Note that out of my whole multi-distro test bed, I've only observed > this issue on Ubuntu 22.04, Ubuntu 20.04, and Fedora 36 Power 9. I > don't have direct access to the test machines, but I spun up an Ubuntu > 22.04 reproducer. It uses gcc version 11.2.0-19ubuntu1. > > A known working Fedora 36 x86_64 system uses gcc version 12.1.1 > 20220507. On that system, snprintf() (or more accurately > __wrap_snprintf()) gets called as expected, instead of the builtin. > There are also RHEL 7 machines in the testbed, so it works fine on > older versions as well. > > Minimal reproducer: > ``` > # cat test.c > #include > void func(const char *s) > { > char buf[16]; > snprintf(buf, 16, "%s", s); > printf("%s\n", buf); > } > int main(void) > { > func("hello world"); > } > > # gcc -g -O2 -fno-builtin -fno-inline test.c -o test > # gdb -q ./test > Reading symbols from ./test... > (gdb) b 5 > Breakpoint 1 at 0x10a0: file test.c, line 9. > (gdb) r > Starting program: /root/git/pacemaker/test > [Thread debugging using libthread_db enabled] > Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1". > > Breakpoint 1, main () at test.c:9 > 9 { > (gdb) s > 10 func("hello world"); > (gdb) > func (s=s@entry=0x55555555600b "hello world") at test.c:3 > 3 { > (gdb) > 5 snprintf(buf, 16, "%s", s); > (gdb) > 0x00005555555551b9 in snprintf (__fmt=, __n= out>, __s=) at > /usr/include/x86_64-linux-gnu/bits/stdio2.h:71 > 71 return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1, > ``` > > Thank you. > > -- > Regards, > > Reid Wahl (He/Him) > Senior Software Engineer, Red Hat > RHEL High Availability - Pacemaker I figured out the Ubuntu issue. `man gcc` under `-O2`: NOTE: In Ubuntu 8.10 and later versions, -D_FORTIFY_SOURCE=2 is set by default, and is activated when -O is set to 2 or higher. This enables additional compile-time and run-time checks for several libc functions. To disable, specify either -U_FORTIFY_SOURCE or -D_FORTIFY_SOURCE=0. I have no idea what's causing the unit test to fail on Fedora 36 Power 9 LE (the only system in the test bed that's still failing), but I don't have a reproducer or enough information to ask a question. I'll try to get one set up this week and go from there. -- Regards, Reid Wahl (He/Him) Senior Software Engineer, Red Hat RHEL High Availability - Pacemaker