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Tue, 19 Jan 2021 03:23:30 -0800 (PST) Received: from [192.168.1.4] ([177.194.48.209]) by smtp.googlemail.com with ESMTPSA id o5sm12100755qti.47.2021.01.19.03.23.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 19 Jan 2021 03:23:29 -0800 (PST) Subject: Re: Glibc 2.31 - time64 with 64-bit kernel and 32-bit userland From: Adhemerval Zanella To: Florian Weimer Cc: Adhemerval Zanella via Libc-help , "Dr. Todor Dimitrov" References: <5FDBA7C2-79E2-4B21-98EF-800694DEB500@technology.de> <87sg6yknoo.fsf@oldenburg.str.redhat.com> <87im7ukmpr.fsf@oldenburg.str.redhat.com> <27f150dc-d721-ac60-bbdf-bd964a99b983@linaro.org> 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 Message-ID: Date: Tue, 19 Jan 2021 08:23:27 -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: <27f150dc-d721-ac60-bbdf-bd964a99b983@linaro.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-7.7 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, 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-help@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-help mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 19 Jan 2021 11:23:33 -0000 On 18/01/2021 18:22, Adhemerval Zanella wrote: > > > On 18/01/2021 17:35, Florian Weimer wrote: >> * Adhemerval Zanella: >> >>>> Should we just undefined __NR_clock_gettime64 for 64-bit AArch64? >>> >>> No, this is armhf default binaries. This situation is similar to >>> i686 running on x86_64 kernels. >> >> It sure looks like it. I wasn't aware that it's possible to run armhfp >> userspace on an AArch64 kernel. >> >> What kind of hardware is needed for that? >> >> (For some reason, Fedora builds its armhfp distribution in a virtualized >> environment.) > > You need a hardware that supports ARMv8 on EL0, was described by > Armv8-A architecture profile (page D13-3255): > > EL3, bits [15:12] > EL3 Exception level handling. Defined values are: > > 0b0000 EL3 is not implemented. > 0b0001 EL3 can be executed in AArch64 state only. > 0b0010 EL3 can be executed in either AArch64 or AArch32 state. > > All other values are reserved. > > EL2, bits [11:8] > EL2 Exception level handling. Defined values are: > > 0b0000 EL2 is not implemented. > 0b0001 EL2 can be executed in AArch64 state only. > 0b0010 EL2 can be executed in either AArch64 or AArch32 state. > > All other values are reserved. > > EL1, bits [7:4] > EL1 Exception level handling. Defined values are: > > 0b0001 EL1 can be executed in AArch64 state only. > 0b0010 EL1 can be executed in either AArch64 or AArch32 state. > > All other values are reserved. > > EL0, bits [3:0] > EL0 Exception level handling. Defined values are: > > 0b0001 EL0 can be executed in AArch64 state only. > 0b0010 EL0 can be executed in either AArch64 or AArch32 state. > > All other values are reserved. > > And unfortunately there is no way to access this special register without > kernel support [2] even with 'cpuid' support (HWCAP_CPUID from hwcap) [3] > this information is masked away due security issues. > > I don't know a easy way to find out without actually issuing a arm32 binary > to find out if the chip does support A32 and T32 state. > > The kernel also limits the compat syscall mechanism (A32 state running on > arm64 chip): > > arch/arm64/Kconfig > > 1213 menuconfig COMPAT > 1214 bool "Kernel support for 32-bit EL0" > 1215 depends on ARM64_4K_PAGES || EXPERT > 1216 select COMPAT_BINFMT_ELF if BINFMT_ELF > 1217 select HAVE_UID16 > 1218 select OLD_SIGSUSPEND3 > 1219 select COMPAT_OLD_SIGACTION > 1220 help > 1221 This option enables support for a 32-bit EL0 running under a 64-bit > 1222 kernel at EL1. AArch32-specific components such as system calls, > 1223 the user helper functions, VFP support and the ptrace interface are > 1224 handled appropriately by the kernel. > 1225 > 1226 If you use a page size other than 4KB (i.e, 16KB or 64KB), please be aware > 1227 that you will only be able to execute AArch32 binaries that were compiled > 1228 with page size aligned segments. > > [1] https://developer.arm.com/documentation/ddi0487/latest/ > [2] https://stackoverflow.com/questions/60071590/reading-armv8-a-registers-with-devmem-from-gnu-linux-shell > [3] https://www.kernel.org/doc/html/latest/arm64/cpu-feature-registers.html > In fact checking with ARM guys there is a way to find it out on Linux: * if the personality(PER_LINUX32) syscall succeeds from an AArch64 process, then 32-bit process support is present >From the commandline: * run 'lscpu': if its output includes the line CPU op-mode(s): 32-bit, 64-bit then both modes are supported; if it says CPU op-mode(s): 64-bit then only 64-bit is supported. If it says neither then the 'lscpu' binary is too old (lscpu is running "personality(PER_LINUX32)" to find this info.)