LinuxCon + CloudOpen + ELC-E Europe 2014

The QEMU machine emulator is used by projects including KVM, Xen, and Linaro to emulate hardware. Low overhead instrumentation is important both for developers and in production. This talk covers how tracing is used in QEMU. QEMU abstracts tracers using a code-generation tool called 'tracetool'. This allows the cross-platform codebase to work with DTrace, SystemTap, LTTng UST, and others. Although tracetool is part of the QEMU source tree, it could also be reused by other projects. Users often wish to get started without installing a tracer, so QEMU provides a built-in tracer called 'simpletrace'. Although it's features are modest, it offers a Python module for writing custom analysis scripts. This makes it a powerful tracer during development. Tracing has been integrated into the very core of QEMU. Recent patches make it possible to trace just-in-time compiled code.