5.3.2. Call Graph Tracing

This section describes how to trace incoming and outgoing function calls.

para-callgraph.stp

#! /usr/bin/env stapfunction trace(entry_p, extra) { %( $# > 1 %? if (tid() in trace) %) printf("%s%s%s %s\n", thread_indent (entry_p), (entry_p>0?"->":"<-"), probefunc (), extra)}%( $# > 1 %?global traceprobe $2.call { trace[tid()] = 1}probe $2.return { delete trace[tid()]}%)probe $1.call { trace(1, $$parms) }probe $1.return { trace(-1, $$return) }

para-callgraph.stp takes two command-line arguments:

The function/s whose entry/exit call you'd like to trace ($1).
A second optional trigger function ($2), which enables or disables tracing on a per-thread basis. Tracing in each thread will continue as long as the trigger function has not exited yet.

para-callgraph.stp uses thread_indent(); as such, its output contains the timestamp, process name, and thread ID of $1 (i.e. the probe function you are tracing). For more information about thread_indent(), refer to its entry in SystemTap Functions.

The following example contains an excerpt from the output for stap para-callgraph.stp 'kernel.function("*@fs/*.c")' 'kernel.function("sys_read")':

Example 5.14. para-callgraph.stp Sample Output

[...] 267 gnome-terminal(2921): <-do_sync_read return=0xfffffffffffffff5 269 gnome-terminal(2921):<-vfs_read return=0xfffffffffffffff5 0 gnome-terminal(2921):->fput file=0xffff880111eebbc0 2 gnome-terminal(2921):<-fput 0 gnome-terminal(2921):->fget_light fd=0x3 fput_needed=0xffff88010544df54 3 gnome-terminal(2921):<-fget_light return=0xffff8801116ce980 0 gnome-terminal(2921):->vfs_read file=0xffff8801116ce980 buf=0xc86504 count=0x1000 pos=0xffff88010544df48 4 gnome-terminal(2921): ->rw_verify_area read_write=0x0 file=0xffff8801116ce980 ppos=0xffff88010544df48 count=0x1000 7 gnome-terminal(2921): <-rw_verify_area return=0x1000 12 gnome-terminal(2921): ->do_sync_read filp=0xffff8801116ce980 buf=0xc86504 len=0x1000 ppos=0xffff88010544df48 15 gnome-terminal(2921): <-do_sync_read return=0xfffffffffffffff5 18 gnome-terminal(2921):<-vfs_read return=0xfffffffffffffff5 0 gnome-terminal(2921):->fput file=0xffff8801116ce980