slackspot [ options ]


slackspot is a utility to decode the trace data collected by the Cobalt core when CONFIG_XENO_OPT_DEBUG_TRACE_RELAX is enabled in the kernel configuration.

This data describes each call hierarchy causing migration to secondary mode (i.e. relaxes) within the application. slackspot presents such data in a human-readable format as symbolic stack backtraces, for helping in debugging spurious relaxes.


slackspot accepts the following options:

--file <trace-file>

Read the trace information to decode from trace-file. By default, trace data is read from /proc/xenomai/debug/relax unless the standard input stream was redirected, in which case stdin is read. In addition, the dash character "-" is interpreted as a placeholder for stdin.

--path <dir[:dir…]>

Search directory list for executables and dynamic libraries. Directories are separatared by a semi-colon within the list. Each directory may be scanned for binary executables when resolving symbols found in stack backtraces.

--filter-in <name=exp[,name=…]>

Only retain backtraces matching the given filters in the output. Each filter is specified by a name=<expr> pair, where name identifies the information field to be matched in the backtrace, and expr is a regular expression which should match such data. Filters are separated by a comma within the list. The available filters are as follows:

  • thread matches the thread name.

  • pid matches the kernel task identifier, i.e. per-task pid.

  • exe matches the name of the main executable being traced.

  • function matches the name of the function being traced.

  • file matches the path of the source file being traced.

  • map matches the path of the mapped executable being traced.

--filter <name=exp[,name=…]>

A shorthand for --filter-in.

--filter-out <name=exp[,name=…]>

Only retain backtraces NOT matching the given filters in the output. This option inverts the sense of matching defined by --filter-in.


A cross-compilation toolchain prefix should be specified for decoding the data obtained from a target system, on a build/development machine. When present, the value of CROSS_COMPILE will be prepended to gcc and addr2line for running the corresponding utilities on the development system.


slackspot appeared in Xenomai 3.0 for the Cobalt real-time core.


In the following scenario, the target system built with the CONFIG_XENO_OPT_DEBUG_TRACE_RELAX feature enabled in the kernel configuration, just ran the /bin/relax program.

This program caused a transition to secondary mode switch of the current task (Task 2) as a result of calling putchar(). The Cobalt core saved the corresponding backtrace information, which is now available from /proc/xenomai/debug/relax on the target system.

Since the target system has limited horsepower, and doesn’t have access to the binary utilities required for decoding the trace data, we will send such data over the network to the host system, in order for the latter to do the decoding and display the call stacks.

We use the standard netcat utility to send and receive the contents of /proc/xenomai/debug/relax over the wire between the target and host systems. The host will also have to mention where the cross-compilation toolchain can be found, by setting the CROSS_COMPILE variable appropriately. The example assumes that /opt/rootfs/MPC5200/lib is the host-based location of the system libraries mounted over NFS onto the target file hierarchy.

On the target system:
target> netcat -l -p 67676 -c < /proc/xenomai/debug/relax
On the host system:
host> netcat target 67676 | CROSS_COMPILE=ppc_6xx- slackspot
      --path=/opt/rootfs/MPC5200/lib:$HOME/frags/relax --filter thread=Task*
Thread[828] "Task 2" started by /bin/relax:
   #0  0xfff00000 ???
   #1  0x000001bb ???
   #2  0x00064393 _IO_file_doallocate() in ??:?
   #3  0x00073d6f _IO_doallocbuf() in ??:?
   #4  0x00072d87 _IO_file_overflow() in ??:?
   #5  0x00075f83 __overflow() in ??:?
   #6  0x0006997b putchar() in ??:?
   #7  0x100017db task2_func() in /home/rpm/frags/relax/relax.c:23
   #8  0x000078d7 task_entry() in /home/rpm/git/xenomai-forge/lib/alchemy/task.c:235
   #9  0x00005a6b start_thread() in pthread_create.c:?
   #10 0x000d389f __clone() in ??:?


slackspot was written by Philippe Gerum <rpm@xenomai.org>.