Restarting macOS actually made this work. I suspect I had previously send pointer to bad data, which may have messed up some kext-related logging until restart. I haven't achieved clarity on when it stops working but sometimes, os_log from a kext reliably stops working.os_log_create also seems to reliably not work from a kext -- no subsystem or cateogry is passed with the associate message:os_log_t general_log = os_log_create("io.myname.test", "general"); os_log(general_log, "hi there"); IOLog("hello from cland v5");but$ log show --predicate 'senderImagePath contains "myname"' --last 5m --info --debug --style json Filtering the log data using "senderImagePath CONTAINS "happy"" [{ "traceID" : 17081085460484, "eventMessage" : "hi there", "eventType" : "logEvent", "source" : null, "formatString" : "hi there", "activityIdentifier" : 0, "subsystem" : "", # <<<<<<< should not be empty "category" : "", # <<<<<<< should not be empty "threadID" : 89482, "senderImageUUID" : "6CE18218-3F80-3215-A933-3F824337FC45", "backtrace" : { "frames" : [ { "imageOffset" : 3883, "imageUUID" : "6CE18218-3F80-3215-A933-3F824337FC45" } ] }, "processImagePath" : "\/kernel", "senderImagePath" : "\/Users\/myname\/kext\/sample.kext\/Contents\/MacOS\/happymeowmeow", "timestamp" : "2019-12-09 20:58:10.361445-0800", "machTimestamp" : 2232376941776, "messageType" : "Default", "processImageUUID" : "DFB5D0E2-3B41-3647-A48B-D704AFCC06B4", "processID" : 0, "senderProgramCounter" : 3883, "parentActivityIdentifier" : 0, "timezoneName" : ""

Hey eksimo,thanks for looking into this. I ran across this same issue today, while working on a fun kext project. Specifically, the code compiles, but I haven't been able to confirm that the log message ends up somewhere retrievable.I'm on:* macOS: 10.14.6 (18G1012)* XCode: Version 11.2.1 (11B500)* kext's macOS Deployment Target: 10.14I compiled a kext that contains:kern_return_t mydemo_start(kmod_info_t * ki, void *d) { const char * cStringVar = "Hello Cruel World!"; os_log(OS_LOG_DEFAULT, "%s", cStringVar); return KERN_SUCCESS; }kext seems to load fine, and it's displayed in kextstat, however log show --predicate 'eventMessage contains "Hello Cruel"' --info doesn't return any messages 😟.Any ideas?