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diff --git a/doc/langref.tex b/doc/langref.tex index 2bc9281d..6003890a 100644 --- a/doc/langref.tex +++ b/doc/langref.tex @@ -992,6 +992,39 @@ For more information about marker probes, see \url{http://sourceware.org/systemtap/wiki/UsingMarkers}. +\subsection{Tracepoints} +\label{sec:tracepoints} +\index{tracepoints} + +This family of probe points hooks to static probing tracepoints +inserted into the kernel or kernel modules. As with marker probes, +these tracepoints are special macro calls inserted by kernel +developers to make probing faster and more reliable than with +DWARF-based probes. DWARF debugging information is not required to +probe tracepoints. Tracepoints have more strongly-typed parameters +than marker probes. + +Tracepoint probes begin with \texttt{kernel}. The next part names the +tracepoint itself: \texttt{trace("name")}. The tracepoint +\texttt{name} string, which can contain wildcard characters, is +matched against the names defined by the kernel developers in the +tracepoint header files. + +The handler associated with a tracepoint-based probe can read the +optional parameters specified at the macro call site. These +parameters are named according to the declaration by the tracepoint +author. For example, the tracepoint probe +\texttt{kernel.trace("sched\_switch")} provides the parameters +\texttt{\$rq}, \texttt{\$prev}, and \texttt{\$next}. If the parameter +is a complex type such as a struct pointer, then a script can access +fields with the same syntax as DWARF \texttt{\$target} variables. +Tracepoint parameters cannot be modified; however, in guru mode a +script can modify fields of parameters. + +The name of the tracepoint is available in \texttt{\$\$name}, and a +string of \texttt{name=value} pairs for all parameters of the +tracepoint is available in \texttt{\$\$vars} or \texttt{\$\$parms}. + \subsection{Timer probes} \index{timer probes} |