libusdt
This is "libusdt", an extraction into a C library of the common parts of ruby-dtrace[1], perl-dtrace[2] and node-dtrace-provider[3].
Those individual language-specific implementations will then become bindings to this library, rather than containing their own implementations of DOF generation and probe creation. Other dynamic language bindings could then easily follow.
The idea here is to allow the specification of a DTrace provider dynamically in code and then create the provider at runtime. This allows providers to be specified in dynamic languages, given suitable bindings.
The general approach is to create two stub functions for each probe, one for the is-enabled check and one for the probe itself. These contain the appropriate instruction sequences to appear to DTrace as compiled-in tracepoints. A minimal DOF document is built describing the provider and indicating these stub functions as the tracepoints, then submitted to the kernel, creating the provider. The API then exposes the stubs, through which the probes may be fired.
Status
The implementation here works as shown in test_usdt.c on Mac OS X, i386 and x86_64, on Solaris-like systems, i386 and x86_64 and on FreeBSD, x86_64 only (so far).
Is-enabled probes are supported and exposed in the API.
There is a "test" target which runs a number of tests of the library, for which perl is required.
OS X builds are Universal by default, and on Solaris, the ARCH variable may be set to either i386 or x86_64 to force a particular build.
FreeBSD builds suffer from broken argument handling; this is a known issue with the current state of DTrace generally on FreeBSD: only the first four arguments work reliably. See:
http://wiki.freebsd.org/DTraceTODO
See Also
There are experimental Lua bindings available, which are a thin layer over this library, and should serve as an example of typical use as a dynamic language extension:
https://github.com/chrisa/lua-usdt
There are also Ruby bindings by Kevin Chan, replacing the provider implementation in ruby-dtrace:
https://github.com/kevinykchan/ruby-usdt
To Do
Platform support:
- add support for FreeBSD 9.0 i386
- add support for Mac OS X PowerPC
- add support for Solaris SPARC
Features:
add a "low level" API, allowing alternative provision of tracepoints for closer integration with language VMs.
support structured types, with close integration with the host DTrace system.
[1] https://github.com/chrisa/ruby-dtrace [2] https://github.com/chrisa/perl-dtrace [3] https://github.com/chrisa/node-dtrace-provider