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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -49 X-Spam_score: -5.0 X-Spam_bar: ----- X-Spam_report: (-5.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-2.907, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 5/27/25 15:42, Markus Armbruster wrote: > Paolo Bonzini writes: > >> Rust makes the current file available as a statically-allocated string, >> but without a NUL terminator. Allow this by storing an optional maximum >> length in the Error. >> >> Note that for portability I am not relying on fprintf's precision >> specifier not accessing memory beyond what will be printed. > > Can you elaborate on the portability problem? I figure ... > >> { >> if (errp == &error_abort) { >> + const char *src = err->src; >> + if (err->src_len >= 0) { >> + /* No need to free it, the program will abort very soon... */ >> + src = g_strndup(err->src, err->src_len); >> + } >> fprintf(stderr, "Unexpected error in %s() at %s:%d:\n", >> - err->func, err->src, err->line); >> + err->func, src, err->line); > > ... you're avoiding the simpler > > fprintf(stderr, "Unexpected error in %s() at %.*s:%d:\n", > err->func, err->src_len, err->src, err->line); > > because of it. I couldn't find anything that says %s is allowed to not be NUL-terminated if a precision is given. That is, whether something like this: char foo[] = {'H', 'e', 'l', 'l', 'o'}; printf("%.5s\n", foo); is guaranteed to work. This is opposed to: 1) strnlen (https://pubs.opengroup.org/onlinepubs/9699919799/functions/strnlen.html), which is guaranteed to examine no more than the number of bytes given by the second character; 2) strndup, for which I found at least a clarification at https://www.austingroupbugs.net/view.php?id=1397. 3) g_strndup, which guarantees that the allocated block is of length n+1 and padded with NULs (though in the case above there will be just one NUL anyway) And also, for strndup/g_strndup it would be quite asinine to implement it using some kind of min(strlen(s), n) but for printf the complexity is greater so you never know. I erred on the side of caution because avoiding an allocation before an abort() isn't particularly interesting. Paolo