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Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <79f2abd2-fe71-006f-d9b4-a3781f292766@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=thuth@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=thuth@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -32 X-Spam_score: -3.3 X-Spam_bar: --- X-Spam_report: (-3.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.351, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.182, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-s390x@nongnu.org, Richard Henderson , David Hildenbrand Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 05/02/2021 09.18, Thomas Huth wrote: > On 05/02/2021 08.08, Christian Borntraeger wrote: >> >> >> On 05.02.21 07:12, Thomas Huth wrote: >>> On 04/02/2021 18.00, Christian Borntraeger wrote: >>>> On 04.02.21 17:41, Thomas Huth wrote: >>>>> According to the "ELF-64 Object File Format" specification: >>>>> >>>>> "The first word in the entry, namesz, identifies the length, in >>>>>    bytes, of a name identifying the entry’s owner or originator. The >>>>> name field >>>>>    contains a null-terminated string, with padding as necessary to >>>>> ensure 8- >>>>>    byte alignment for the descriptor field. The length does not include >>>>> the >>>>>    terminating null or the padding." >>>>> >>>>> So we should not include the terminating NUL in the length field here. >>>>> >>>>> Also there is a compiler warning with GCC 9.3 when compiling with >>>>> the -fsanitize=thread compiler flag: >>>>> >>>>>    In function 'strncpy', >>>>>       inlined from 's390x_write_elf64_notes' at >>>>> ../target/s390x/arch_dump.c:219:9: >>>>>    /usr/include/x86_64-linux-gnu/bits/string_fortified.h:106:10: error: >>>>>     '__builtin_strncpy' specified bound 8 equals destination size >>>>>     [-Werror=stringop-truncation] >>>>> >>>>> Since the name should always be NUL-terminated, let's use g_strlcpy() to >>>>> silence this warning. And while we're at it, also add an assert() to make >>>>> sure that the provided names always fit the size field (which is fine for >>>>> the current callers, the function is called once with "CORE" and once with >>>>> "LINUX" as a name). >>>>> >>>>> Signed-off-by: Thomas Huth >>>>> --- >>>>>    v2: Use g_strlcpy instead of strncpy >>>> >>>> >>>> With this patch I do get >>>> >>>> WARNING: possibly corrupt Elf64_Nhdr: n_namesz: 0 n_descsz: 4 n_type: 88 >>>> >>>> when running crash on the elf file created by dump-guest-memory. Without >>>> the >>>> patch everything is fine. >>> >>> Drat! Looking at the crash sources: >>> >>>   https://github.com/crash-utility/crash/blob/master/s390x.c#L378 >>> >>> ... it seems like crash is rather rounding up to the next 4 bytes >>> boundary instead of the next 8 bytes boundary. Thus things go wrong now >>> when QEMU writes writes the "CORE" notes section. In the old code we were >>> using 4 + 1 as a lengths, so crash correctly rounded this up to 8. But >>> now with 4 as a length, this does not work right anymore :-( >>> >>> Seems like I either misunderstood the "ELF-64 Object File Format" >>> specification, or this is a bug in the crash utility (it should either >>> add 1 to n_namesz for the trailing NUL or pad to 8 instead of 4)? Anyway, >>> it's maybe better to keep the "+ 1" in QEMU for now to avoid breaking >>> things, I guess? >> >> I guess kdump and friends are also doing the +1 otherwise we would see the >> error with those ELF dumps. >> But yes, as long as crash does not work we must not apply this patch. > > Looking at the other target/*/arch_dump.c files, it also seems like they > include the NUL in the namesz field for their 64-bit flavours ... I've got > the feeling that the "ELF-64 Object File Format" spec simply does not apply > here, or I must have missed something else. After searching for a little bit longer, I guess this is the spec that applies nowadays: http://www.sco.com/developers/gabi/latest/ch5.pheader.html#note_section Citing: "The first namesz bytes in name contain a null-terminated character representation of the entry's owner or originator." So the NUL should be included in the namesz field, indeed. Thomas