error::dwarf(7stap) [centos man page]
ERROR::DWARF(7stap) ERROR::DWARF(7stap) NAME
error::dwarf - dwarf debuginfo quality problems DESCRIPTION
Systemtap sometimes relies on ELF/DWARF debuginfo for programs being instrumented to locate places to probe, or context variables to read/write, just like a symbolic debugger does. Even though examination of the program's source code may show variables or lines where probes may be desired, the compiler must preserve information about them for systemtap (or a debugger such as gdb) to get pinpoint access to the desired information. If a script requires such data, but the compiler did not preserve enough of it, pass-2 errors may result. Common conditions that trigger these problems include; compiler version Prior to GCC version 4.5, debuginfo quality was fairly limited. Often developers were advised to build their programs with -O0 -g flags to disable optimization. GCC version 4.5 introduced a facility called "variable-tracking assignments" that allows it to gen- erate high-quality debuginfo under full -O2 -g optimization. It is not perfect, but much better than before. Note that, due to another gcc bug (PR51358) -O0 -g can actually sometimes make debuginfo quality worse than for -O2 -g. function inlining Even modern gcc sometimes has problems with parameters for inlined functions. It may be necessary to change the script to probe at a slightly different place (try a .statement() probe, instead of a .function() probe, somewhere a few source lines into the body of the inlined function. Or try putting a probe at the call site of the inlined function. Or use the if @defined($var) { ... } script language construct to test for the resolvability of the context variable before using it. instruction reordering Heavily optimized code often smears the instructions from multiple source statements together. This can leave systemtap with no place to choose to place a probe, especially a statement probe specified by line number. Systemtap may advise to try a nearby line number, but these may not work well either. Consider placing a probe by a statement wildcard or line number range. ALTERNATIVES
In order to reduce reliance on ELF/DWARF debuginfo, consider the use of statically compiled-in instrumentation, such as kernel tracepoints, or <sys/sdt.h> userspace markers. Such instrumentation hook sites are relatively low cost (just one NOP instruction for sdt.h), and nearly guarantee the availability of parameter data and a reliable probe site, all without reliance on debuginfo. SEE ALSO
stap(1), http://dwarfstd.org/, http://sourceware.org/systemtap/wiki/TipContextVariables, http://gcc.gnu.org/wiki/Var_Tracking_Assignments, warning::debuginfo(7stap), error::reporting(7stap) ERROR::DWARF(7stap)
Check Out this Related Man Page
STAP(7) Miscellaneous Information Manual STAP(7) NAME
stappaths - systemtap configurable file paths DESCRIPTION
This manual page was generated on 2014-06-09 for systemtap 2.4. The following section will list the main paths in systemtap that are important to know and may be required to reference. /usr/share/systemtap/tapset/ The directory for the standard probe-alias / function tapset library, unless overridden by the SYSTEMTAP_TAPSET environment variable or the XDG_DATA_DIRS environment variable. These are described in the stapprobes(3stap), probe::*(3stap), and function::*(3stap) manual pages. /usr/share/systemtap/runtime/ The runtime sources, unless overridden by the SYSTEMTAP_RUNTIME environment variable. /usr/bin/staprun The auxiliary program supervising module loading, interaction, and unloading. /usr/libexec/systemtap/stapio The auxiliary program for module input and output handling. /usr/include/sys/sdt.h Location of the <sys/sdt.h> headers. Kernel debuginfo Path: /usr/lib/debug/lib/modules/$(uname -r)/ The location of kernel debugging information when packaged into the kernel-debuginfo RPM, unless overridden by the SYSTEMTAP_DEBUG- INFO_PATH environment variable. The default value for this variable is +:.debug:/usr/lib/debug:build. elfutils searches vmlinux in this path and it interprets the path as a base directory of which various subdirectories will be searched for finding debuginfo for the kernel, kernel modules, and user-space binaries. By default, systemtap will also look for vmlinux in these locations: /boot/vmlinux-`uname -r` /lib/modules/`uname -r`/vmlinux /lib/modules/`uname -r`/vmlinux.debug /lib/modules/`uname -r`/build/vmlinux /lib/modules/`uname -r`/.debug/vmlinux.debug /usr/lib/debug/lib/modules/`uname -r`/vmlinux.debug /var/cache/abrt-di/usr/debug/lib/modules/`uname -r`/ /var/cache/abrt-di/usr/lib/debug/lib/modules/`uname -r`/vmlinux.debug Corresponding source files are usually located under /usr/src/debug/. Further file information on user-space applications can be determined per-basis using rpm -ql <package>-debuginfo. For supported user-space applications information please visit the systemtap wiki. $HOME/.systemtap Systemtap data directory for cached systemtap files, unless overridden by the SYSTEMTAP_DIR environment variable. /tmp/stapXXXXXX Temporary directory for systemtap files, including translated C code and kernel object. /lib/modules/VERSION/build The location of kernel module building infrastructure. /usr/share/doc/systemtap*/examples Examples with greater detail can be found here. Each example comes with a .txt or .meta file explaining what the example, sample or demo does and how it is ordinarily run. $SYSTEMTAP_DIR/ssl/server User's server-side SSL certificate database. If SYSTEMTAP_DIR is not set, the default is $HOME/.systemtap. $SYSTEMTAP_DIR/ssl/client User's private client-side SSL certificate database. If SYSTEMTAP_DIR is not set, the default is $HOME/.systemtap. /etc/systemtap/ssl/client Global client-side SSL certificate database. /etc/systemtap/staprun/ staprun's trusted signer certificate database. /etc/sysconfig/stap-server/ stap-server service global configuration file. /etc/stap-server/conf.d/*.conf stap-server service configuration files for default servers. /var/run/stap-server/ stap-server service default location of status files for running servers. /var/log/stap-server/log stap-server service default log file. FILES
/usr/share/systemtap/tapset SEE ALSO
stapprobes(3stap), staprun(8), stapvars(3stap), stapex(3stap), stap-server(8), awk(1), gdb(1) BUGS
Use the Bugzilla link of the project web page or our mailing list. http://sourceware.org/systemtap/,<systemtap@sourceware.org>. Systemtap Team STAP(7)