{"record":{"id":"ff229e66bb51684b","repo":"go-delve/delve","slug":"failed-to-set-xstate-v","errorCode":null,"errorMessage":"failed to set xstate: %v","messagePattern":"failed to set xstate: (.+?)","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"error","filePath":"pkg/proc/native/ptrace_freebsd_amd64.go","lineNumber":62,"sourceCode":"// ptraceGetXsave gets the X86 XSAVE data for the given tid.\nfunc ptraceGetXsave(tid int) ([]byte, error) {\n\tlen, err := ptraceXsaveLen(tid)\n\tif err != nil {\n\t\treturn nil, err\n\t}\n\txsaveBuf := make([]byte, len)\n\tret, err := C.ptrace(C.PT_GETXSTATE, C.pid_t(tid), C.caddr_t(unsafe.Pointer(&xsaveBuf[0])), C.int(len))\n\tif ret != 0 {\n\t\treturn nil, fmt.Errorf(\"failed to get xstate: %v\", err)\n\t}\n\treturn xsaveBuf, nil\n}\n\n// ptraceSetXsave sets the X86 XSAVE data for the given tid.\nfunc ptraceSetXsave(tid int, xsaveBuf []byte) error {\n\tret, err := C.ptrace(C.PT_SETXSTATE, C.pid_t(tid), C.caddr_t(unsafe.Pointer(&xsaveBuf[0])), C.int(len(xsaveBuf)))\n\tif ret != 0 {\n\t\treturn fmt.Errorf(\"failed to set xstate: %v\", err)\n\t}\n\treturn nil\n}\n\nfunc ptraceGetRegset(id int) (*amd64util.AMD64Xstate, error) {\n\tvar regset amd64util.AMD64Xstate\n\tret, err := C.ptrace(C.PT_GETFPREGS, C.pid_t(id), C.caddr_t(unsafe.Pointer(&regset.AMD64PtraceFpRegs)), C.int(0))\n\tif ret != 0 {\n\t\treturn nil, fmt.Errorf(\"failed to get FP registers: %v\", err)\n\t}\n\tregset.Xsave, err = ptraceGetXsave(id)\n\tif err != nil {\n\t\treturn nil, err\n\t}\n\terr = amd64util.AMD64XstateRead(regset.Xsave, false, &regset, cpuid.AMD64XstateZMMHi256Offset())\n\treturn &regset, err\n}\n","sourceCodeStart":44,"sourceCodeEnd":80,"githubUrl":"https://github.com/go-delve/delve/blob/a23773e6c31361e43246bc43a424ee009679b174/pkg/proc/native/ptrace_freebsd_amd64.go#L44-L80","documentation":"ptraceSetXsave writes the thread's extended XSAVE state back with PT_SETXSTATE on FreeBSD/amd64. A non-zero return from ptrace is wrapped in this error. It means the kernel refused the xstate write (invalid buffer length, unsupported features in the buffer, or dead thread).","triggerScenarios":"ptraceSetRegset -> ptraceSetXsave when the xsave buffer size does not match what the kernel expects for the CPU's enabled xstate features, the tid has exited, or PT_SETXSTATE is unsupported by the running kernel.","commonSituations":"Setting registers after the debuggee thread died; kernel/CPU with different XSAVE feature set than the buffer captured earlier (e.g. after exec of a new binary); running in restricted environments (jails/VMs) lacking xstate write support.","solutions":["Confirm the target thread is alive before calling SetRegs-style register writes","Ensure the xsave buffer length matches the CPU's xstate size (query once via PT_GETXSTATE and reuse that length)","Upgrade/verify the FreeBSD kernel supports PT_SETXSTATE for the running CPU","Capture errno properly if the formatted error is empty to identify the true cause"],"exampleFix":"// before\nif regset.Xsave != nil {\n\treturn ptraceSetXsave(id, regset.Xsave)\n}\n// after\nif regset.Xsave != nil {\n\tif err := ptraceSetXsave(id, regset.Xsave); err != nil {\n\t\treturn fmt.Errorf(\"setxstate tid=%d: %w\", id, err)\n\t}\n}","handlingStrategy":"validation","validationCode":"// before writing xstate\nif !isThreadAlive(dbp, id) {\n\treturn fmt.Errorf(\"thread %d gone; skipping xstate write\", id)\n}\nif len(xsaveBuf) != knownXstateSize {\n\treturn fmt.Errorf(\"xstate buffer %d != expected %d\", len(xsaveBuf), knownXstateSize)\n}","typeGuard":"func isXstateWriteErr(err error) bool {\n\treturn err != nil && strings.Contains(err.Error(), \"failed to set xstate\")\n}","tryCatchPattern":null,"preventionTips":["Re-read the xstate (PT_GETXSTATE) immediately before modifying so buffer size/features match the CPU","Write registers only while the thread is stopped and alive","Test xstate write support once at attach; disable FP register editing if unsupported"],"tags":["freebsd","ptrace","registers","xsave","cgo"],"backgroundTag":"ptrace-xstate-write-failed","analyzedSha":"a23773e6c31361e43246bc43a424ee009679b174","analyzedAt":"2026-08-31T15:12:45.221Z","schemaVersion":2},"datasetVersion":"2026-08-31T19:17:28.585Z"}