DESCRIPTION

For many symbolic probing operations, systemtap needs DWARF debuginfo for the relevant binaries. This often includes resolving function/statement probes, or $context variables in related handlers. DWARF debuginfo may be found in the original binaries built during compilation, or may have been split into separate files. The SYSTEMTAP_DEBUGINFO_PATH environment variable affects where systemtap looks for these files.

If your operating system came from a distributor, check with them if debuginfo packages or variants are available. If your distributor does not have debuginfo-equipped binaries at all, you may need to rebuild it.

Systemtap uses the elfutils library to process ELF/DWARF files. The version of elfutils used by systemtap is the number after the slash in the -V output:

% stap -V
Systemtap translator/driver (version 2.3/0.156, rpm 2.3-1.fc19)
Copyright (C) 2005-2014 Red Hat, Inc. and others
[...]

This indicates systemtap version 2.3 with elfutils version 0.156.

kernel debuginfo

For scripts that target the kernel, systemtap may search for the vmlinux file created during its original build. This is distinct from the boot-loader's compressed/stripped vmlinuz file, and much larger. If you have a hand-built kernel, make sure it was built with the CONFIG_DEBUG_INFO=y option. Some Linux distributions may include several kernel variants, including a confusingly named kernel-debug (an alternative kernel, with its own kernel-debug-debuginfo package), which is not the same thing as the kernel-debuginfo (DWARF data for the base kernel). The stap-prep program can help install the right set.

process debuginfo

For scripts that target user-space, systemtap may search for debuginfo. If you have hand-built binaries, use CFLAGS=-g -O2 to compile them.

minidebuginfo

On some systems, binaries may be compiled with a subset of debuginfo useful for function tracing and backtraces. This 'Minidebuginfo' is a xz compressed section labeled .gnu_debugdata. Support for minidebuginfo relies on elfutils version 0.156 or later.

compressed debuginfo

On some systems, debuginfo may be available, but compressed into .zdebug_* sections. Support for compressed debuginfo relies on elfutils version 0.153 or later.

unnecessary debuginfo

In some cases, a script may be altered to avoid requiring debuginfo. For example, as script that uses probe syscall.* probes could try instead probe nd_syscall.* (for non-DWARF syscall): these work similarly, and use more intricate (fragile) tapset functions to extract system call arguments. Another option is use of compiled-in instrumentation such as kernel tracepoints or user-space <sys/sdt.h> markers in libraries or executables, which do not require debuginfo. If debuginfo was required for resolving a complicated $var->foo->bar expression, it may be possible to use @cast(var,foo,foo.h)->foo->bar to synthesize debuginfo for that type from a header file.

AUTOMATION

On some platforms, systemtap may advise what commands to run, in order to download needed debuginfo. Another possibility is to invoke systemtap with the --download-debuginfo flag. The stap-prep script included with systemtap may be able to download the appropriate kernel debuginfo. Another possibility is to install and use a stap-server remote-compilation instance on a machine on your network, where debuginfo and compilation resources can be centralized. Try the stap --use-server option, in case such a server is already running.