From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qv1-xf2d.google.com (mail-qv1-xf2d.google.com [IPv6:2607:f8b0:4864:20::f2d]) by sourceware.org (Postfix) with ESMTPS id 6C8CD389041B for ; Tue, 23 Feb 2021 11:56:26 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 6C8CD389041B Received: by mail-qv1-xf2d.google.com with SMTP id p12so7594538qvv.5 for ; Tue, 23 Feb 2021 03:56:26 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:to:cc:references:from:autocrypt:subject :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=buSaiB4vgTJXOMJ7tMzvZXLkYZepS91K0PnhantCO4s=; b=PvdDQcK7j3f1ONEhBbzkq4upIc3k98dYvfxTyV+dWPeY9cgcuttJ1CJ4EyXfqpous7 i+qw3BUhfylEPJc+s9weUnfh6YBkSfden6NqJv9s4vEOBDq0Y3DJ8zid8UiayB5D3xY2 58J0Dl291xrQ5OHqFsPTvkRJ5660Mq/RdnrZXWp/mnGNBLg3QiTTiSh/Z9g4mxybJ938 TXnwY9RfaLqs0XI0bOiuWu+nJ+uFP9mUpZEI7lvnf4vIUVHJzxDIU1RjPkgfrJPxMuu1 K0oefomxHttgLhoJozQUCIv/G2A3YFAElyufTJqA/xT+dkfBG1RxEOPwu/mBVMtGRAVN cWpQ== X-Gm-Message-State: AOAM533otOMJfDNLq1AdZ/XpbojbPGGUcnI+/O6YTR0ybjOz9T4xMo/e SCWxx5wxtZ/HZX8jLhREy9PegA== X-Google-Smtp-Source: ABdhPJxwf14n1TH/yGXo/yL5Qtx5FPopmxcv/Q8MWwrOk6Qa271Z4eyQ+V4wON79p/zr+PSm0k1U2g== X-Received: by 2002:a0c:c790:: with SMTP id k16mr25756248qvj.31.1614081385960; Tue, 23 Feb 2021 03:56:25 -0800 (PST) Received: from [192.168.1.4] ([177.194.48.209]) by smtp.googlemail.com with ESMTPSA id j67sm14807885qke.85.2021.02.23.03.56.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 23 Feb 2021 03:56:25 -0800 (PST) To: Tulio Magno Quites Machado Filho , Florian Weimer Cc: libc-alpha@sourceware.org, Raoni Fassina Firmino References: <20210212170941.1786380-1-adhemerval.zanella@linaro.org> <878s7ti4m0.fsf@oldenburg.str.redhat.com> <90d1d0e5-a31e-fbac-ead0-7f76f2645cd9@linaro.org> <87sg5n3g04.fsf@linux.ibm.com> From: Adhemerval Zanella Autocrypt: addr=adhemerval.zanella@linaro.org; prefer-encrypt=mutual; keydata= mQINBFcVGkoBEADiQU2x/cBBmAVf5C2d1xgz6zCnlCefbqaflUBw4hB/bEME40QsrVzWZ5Nq 8kxkEczZzAOKkkvv4pRVLlLn/zDtFXhlcvQRJ3yFMGqzBjofucOrmdYkOGo0uCaoJKPT186L NWp53SACXguFJpnw4ODI64ziInzXQs/rUJqrFoVIlrPDmNv/LUv1OVPKz20ETjgfpg8MNwG6 iMizMefCl+RbtXbIEZ3TE/IaDT/jcOirjv96lBKrc/pAL0h/O71Kwbbp43fimW80GhjiaN2y WGByepnkAVP7FyNarhdDpJhoDmUk9yfwNuIuESaCQtfd3vgKKuo6grcKZ8bHy7IXX1XJj2X/ BgRVhVgMHAnDPFIkXtP+SiarkUaLjGzCz7XkUn4XAGDskBNfbizFqYUQCaL2FdbW3DeZqNIa nSzKAZK7Dm9+0VVSRZXP89w71Y7JUV56xL/PlOE+YKKFdEw+gQjQi0e+DZILAtFjJLoCrkEX w4LluMhYX/X8XP6/C3xW0yOZhvHYyn72sV4yJ1uyc/qz3OY32CRy+bwPzAMAkhdwcORA3JPb kPTlimhQqVgvca8m+MQ/JFZ6D+K7QPyvEv7bQ7M+IzFmTkOCwCJ3xqOD6GjX3aphk8Sr0dq3 4Awlf5xFDAG8dn8Uuutb7naGBd/fEv6t8dfkNyzj6yvc4jpVxwARAQABtElBZGhlbWVydmFs IFphbmVsbGEgTmV0dG8gKExpbmFybyBWUE4gS2V5KSA8YWRoZW1lcnZhbC56YW5lbGxhQGxp bmFyby5vcmc+iQI3BBMBCAAhBQJXFRpKAhsDBQsJCAcDBRUKCQgLBRYCAwEAAh4BAheAAAoJ EKqx7BSnlIjv0e8P/1YOYoNkvJ+AJcNUaM5a2SA9oAKjSJ/M/EN4Id5Ow41ZJS4lUA0apSXW NjQg3VeVc2RiHab2LIB4MxdJhaWTuzfLkYnBeoy4u6njYcaoSwf3g9dSsvsl3mhtuzm6aXFH /Qsauav77enJh99tI4T+58rp0EuLhDsQbnBic/ukYNv7sQV8dy9KxA54yLnYUFqH6pfH8Lly sTVAMyi5Fg5O5/hVV+Z0Kpr+ZocC1YFJkTsNLAW5EIYSP9ftniqaVsim7MNmodv/zqK0IyDB GLLH1kjhvb5+6ySGlWbMTomt/or/uvMgulz0bRS+LUyOmlfXDdT+t38VPKBBVwFMarNuREU2 69M3a3jdTfScboDd2ck1u7l+QbaGoHZQ8ZNUrzgObltjohiIsazqkgYDQzXIMrD9H19E+8fw kCNUlXxjEgH/Kg8DlpoYJXSJCX0fjMWfXywL6ZXc2xyG/hbl5hvsLNmqDpLpc1CfKcA0BkK+ k8R57fr91mTCppSwwKJYO9T+8J+o4ho/CJnK/jBy1pWKMYJPvvrpdBCWq3MfzVpXYdahRKHI ypk8m4QlRlbOXWJ3TDd/SKNfSSrWgwRSg7XCjSlR7PNzNFXTULLB34sZhjrN6Q8NQZsZnMNs TX8nlGOVrKolnQPjKCLwCyu8PhllU8OwbSMKskcD1PSkG6h3r0AquQINBFcVGkoBEACgAdbR Ck+fsfOVwT8zowMiL3l9a2DP3Eeak23ifdZG+8Avb/SImpv0UMSbRfnw/N81IWwlbjkjbGTu oT37iZHLRwYUFmA8fZX0wNDNKQUUTjN6XalJmvhdz9l71H3WnE0wneEM5ahu5V1L1utUWTyh VUwzX1lwJeV3vyrNgI1kYOaeuNVvq7npNR6t6XxEpqPsNc6O77I12XELic2+36YibyqlTJIQ V1SZEbIy26AbC2zH9WqaKyGyQnr/IPbTJ2Lv0dM3RaXoVf+CeK7gB2B+w1hZummD21c1Laua +VIMPCUQ+EM8W9EtX+0iJXxI+wsztLT6vltQcm+5Q7tY+HFUucizJkAOAz98YFucwKefbkTp eKvCfCwiM1bGatZEFFKIlvJ2QNMQNiUrqJBlW9nZp/k7pbG3oStOjvawD9ZbP9e0fnlWJIsj 6c7pX354Yi7kxIk/6gREidHLLqEb/otuwt1aoMPg97iUgDV5mlNef77lWE8vxmlY0FBWIXuZ yv0XYxf1WF6dRizwFFbxvUZzIJp3spAao7jLsQj1DbD2s5+S1BW09A0mI/1DjB6EhNN+4bDB SJCOv/ReK3tFJXuj/HbyDrOdoMt8aIFbe7YFLEExHpSk+HgN05Lg5TyTro8oW7TSMTk+8a5M kzaH4UGXTTBDP/g5cfL3RFPl79ubXwARAQABiQIfBBgBCAAJBQJXFRpKAhsMAAoJEKqx7BSn lIjvI/8P/jg0jl4Tbvg3B5kT6PxJOXHYu9OoyaHLcay6Cd+ZrOd1VQQCbOcgLFbf4Yr+rE9l mYsY67AUgq2QKmVVbn9pjvGsEaz8UmfDnz5epUhDxC6yRRvY4hreMXZhPZ1pbMa6A0a/WOSt AgFj5V6Z4dXGTM/lNManr0HjXxbUYv2WfbNt3/07Db9T+GZkpUotC6iknsTA4rJi6u2ls0W9 1UIvW4o01vb4nZRCj4rni0g6eWoQCGoVDk/xFfy7ZliR5B+3Z3EWRJcQskip/QAHjbLa3pml xAZ484fVxgeESOoaeC9TiBIp0NfH8akWOI0HpBCiBD5xaCTvR7ujUWMvhsX2n881r/hNlR9g fcE6q00qHSPAEgGr1bnFv74/1vbKtjeXLCcRKk3Ulw0bY1OoDxWQr86T2fZGJ/HIZuVVBf3+ gaYJF92GXFynHnea14nFFuFgOni0Mi1zDxYH/8yGGBXvo14KWd8JOW0NJPaCDFJkdS5hu0VY 7vJwKcyHJGxsCLU+Et0mryX8qZwqibJIzu7kUJQdQDljbRPDFd/xmGUFCQiQAncSilYOcxNU EMVCXPAQTteqkvA+gNqSaK1NM9tY0eQ4iJpo+aoX8HAcn4sZzt2pfUB9vQMTBJ2d4+m/qO6+ cFTAceXmIoFsN8+gFN3i8Is3u12u8xGudcBPvpoy4OoG Subject: Re: [PATCH] powerpc: Remove backtrace implementation Message-ID: Date: Tue, 23 Feb 2021 08:56:22 -0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <87sg5n3g04.fsf@linux.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-7.6 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, KAM_SHORT, NICE_REPLY_A, 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 X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 23 Feb 2021 11:56:28 -0000 On 22/02/2021 19:16, Tulio Magno Quites Machado Filho wrote: > Adhemerval Zanella writes: > >> On 12/02/2021 14:21, Florian Weimer wrote: >>> * Adhemerval Zanella: >>> >>> Does this really work well (enough) on systems which do not build >>> everything with asynchronous unwind tables? If I recall correctly, GCC >>> enabled them by default only quite recently. >> >> This should work as well any other architecture since it uses the libgcc_s >> routines. Afaik the powerpc implementation was done as optimization, not >> for correctness. > > I think Florian is correct. > > GCC enabled -fasynchronous-unwind-tables by default on ppc* ELF targets on > version 8 [1]. > So if you take a Debian 10 ppc64le, build the backtrace example from > linux-manpages [2] with gcc-7 or with a newer GCC using > 'gcc-9 -g0 -fno-asynchronous-unwind-tables', this executable won't be able to > print the correct backtrace, e.g.: > > $ ./testrun.sh ./tst-no-asynchronous-unwind-tables 3 > backtrace() returned 1 addresses > ./tst-no-asynchronous-unwind-tables(+0xb48) [0x7fff99a00b48] > > 8 addresses were expected in the previous test. > > With that said, I don't think the powerpc files are just an optimization and > removing them may cause old binaries to stop getting the right backtrace. > > [1] https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=0359465c703a > [2] https://www.man7.org/linux/man-pages/man3/backtrace.3.html > Afaik this is true for every other architecture that uses libgcc for backtrace implementation, currently *everything* but powerpc and microblaze: This is on aarch64 with gcc 5.4: $ gcc -g0 -fno-asynchronous-unwind-tables backtrace.c -o backtrace $ ./backtrace 3 backtrace() returned 1 addresses ./backtrace() [0x4009dc] And this is sparc64 with gcc-10: $ gcc -g0 -fno-asynchronous-unwind-tables backtrace.c -o backtrace $ ./backtrace 3 backtrace() returned 1 addresses ./backtrace(+0xa74) [0x10000000a74] So for all other architectures we require -fasynchronous-unwind-tables to get backtrace work and I plan to remove microblaze implementation so powerpc will be only outlier. The question is: should we fix all other architectures to provide a non-libgcc way to get around this issue? What about architectures that backtrace through frame layout is not really possible or require hackish ways (-fomit-frame-pointer for some architecture or thumb mode with gcc and clang objects)? I really don't think we should keep this fast-unwinders (sanitizers has a hard time maintaining for some architectures) so I still think we should move to use *just* libgcc as backend and document the flags required to get a meaningful stacktrace