where the trace file  "trace-*"  

I compile qemu-system-aarch64 with  --enable-trace-backends=simple  option, then start qemu with -trace nvme*  , qemu start successful but I cann't find the trace file  "trace-*" at qemu started  directory.

I tested qemu.git/master on Linux x86_64 to confirm that the simple trace backend works. trace-$pid files are written to the current working directory.

If QEMU prints a warning that the trace event name does not exist, try escaping the asterisk on your command-line: -trace nvme\*

You can find the trace-event files in the source tree, if you were talking about those. Anyway, this does not really sound like a bug, so I'm closing this ticket now. If you need general help, please use the qemu-discuss mailing list or the #qemu channel on OFTC IRC instead.