+@node List of environment variables detected by libust
+@appendix List of environment variables detected by libust
+
+The behavior of tracing can be influenced by setting special environment
+variables in the environment of the traced application. This section
+describes these variables.
+
+@itemize @bullet
+
+@item
+@env{UST_TRACE}
+
+If set to 1, start tracing as soon as the program starts. Tracing is
+guaranteed to be started by the time the @code{main()} function starts.
+
+@item
+@env{UST_AUTOPROBE}
+
+If set to @code{1}, enable all markers by the time the @code{main()} function starts.
+
+@item
+@env{UST_AUTOCOLLECT}
+
+If set to @code{0}, disable notification of daemon on trace start. Useful for
+performance tests.
+
+@item
+@env{UST_OVERWRITE}
+
+If set to @code{1}, enable overwriting of buffers on overrun.
+
+@item
+@env{UST_SUBBUF_NUM}
+
+If set, defines the default number of subbuffers per buffer.
+
+@item
+@env{UST_SUBBUF_SIZE}
+
+If set, defines the default size of subbuffers, in bytes.
+
+@end itemize
+
+@node GDB integration
+@appendix GDB integration
+
+GDB, the GNU Debugger, can use UST markers as GDB tracepoints (note GDB has its
+own concept of tracepoint). This feature is called GDB Static Tracepoints. When
+a GDB tracepoint is hit, GDB collects the marker arguments, as well as the
+state of the registers.
+
+In UST, support for GDB integration is not compiled in by default because of
+the cost of saving registers when a marker is hit. To enable it, run the
+@command{./configure} script with the @code{-DCONFIG_UST_GDB_INTEGRATION} flag
+in the @env{CFLAGS} environment variable. For example:
+
+@example
+@verbatim
+
+CFLAGS=-DCONFIG_UST_GDB_INTEGRATION ./configure
+
+@end verbatim
+@end example
+
+As of this writing, GDB Static Tracepoints have been submitted
+(@url{http://sourceware.org/ml/gdb-patches/2010-06/msg00592.html}) to the GDB
+mailing list.
+
+GDB integration is currently only supported on x86-32 and x86-64.