can optimize out trace events completely. This is the default and imposes no
performance penalty.
+=== Stderr ===
+
+The "stderr" backend sends trace events directly to standard error. This
+effectively turns trace events into debug printfs.
+
+This is the simplest backend and can be used together with existing code that
+uses DPRINTF().
+
=== Simpletrace ===
The "simple" backend supports common use cases and comes as part of the QEMU
trace backends but it is portable. This is the recommended trace backend
unless you have specific needs for more advanced backends.
-=== Stderr ===
-
-The "stderr" backend sends trace events directly to standard error output
-during emulation.
+Warning: the "simple" backend is not thread-safe so only enable trace events
+that are executed while the global mutex is held. Much of QEMU meets this
+requirement but some utility functions like qemu_malloc() or thread-related
+code cannot be safely traced using the "simple" backend.
==== Monitor commands ====
The "ust" backend uses the LTTng Userspace Tracer library. There are no
monitor commands built into QEMU, instead UST utilities should be used to list,
enable/disable, and dump traces.
+
+=== SystemTap ===
+
+The "dtrace" backend uses DTrace sdt probes but has only been tested with
+SystemTap. When SystemTap support is detected a .stp file with wrapper probes
+is generated to make use in scripts more convenient. This step can also be
+performed manually after a build in order to change the binary name in the .stp
+probes:
+
+ scripts/tracetool --dtrace --stap \
+ --binary path/to/qemu-binary \
+ --target-type system \
+ --target-arch x86_64 \
+ <trace-events >qemu.stp