fbt
Provider
This section describes the Function Boundary Tracing (FBT) provider, which
provides probes associated with the entry to and return from most functions
in the Oracle Solaris kernel. A function is the fundamental unit of program
text. In a well-designed system, each function performs a discrete and
well-defined operation on a specified object or series of like objects.
Therefore, even on the smallest Oracle Solaris systems,
fbt
provides 20,000 probes.
Similar to other DTrace providers, fbt
has no probe effect
when it is not explicitly enabled. When enabled, fbt
only
induces a probe effect in probed functions. While the fbt
implementation is highly specific to the instruction set architecture,
fbt
has been implemented on both SPARC and x86
platforms. For each instruction set, there are a small number of functions
that do not call other functions and are highly optimized by the compiler,
called leaf functions, that cannot be instrumented by
fbt
. Probes for these functions are not present in
DTrace.
Effective use of fbt
probes requires knowledge of the
operating system implementation. Therefore, it is recommended that you use
fbt
only when developing kernel software or when
other providers are not sufficient. Other DTrace providers, including
syscall
, sched
,
proc
, and io
, can be used to
answer most system analysis questions without requiring operating system
implementation knowledge.