Documentation: document undefined behavior for NULL pointers

[lttng-ust.git] / doc / man / lttng-ust.3

diff --git a/doc/man/lttng-ust.3 b/doc/man/lttng-ust.3
index 88025c0e702727da568f9a99b7dbb70bd248cc2c..8286e568b64ec915280aae67d1c589261fdb7545 100644 (file)
--- a/doc/man/lttng-ust.3
+++ b/doc/man/lttng-ust.3
@@ -1,7 +1,7 @@
 .TH "LTTNG-UST" "3" "February 16, 2012" "" ""
 
 .SH "NAME"
-lttng-ust \(em Linux Trace Toolkit Next Generation User-Space Tracer
+lttng-ust \(em Linux Trace Toolkit Next Generation User-Space Tracer 2.x
 
 .SH "SYNOPSIS"
 
@@ -116,6 +116,7 @@ TRACEPOINT_EVENT(
                 * ctf_array_text: a statically-sized array, printed as
                 * a string. No need to be terminated by a null
                 * character.
+                * Behavior is undefined if "text" field is NULL.
                 */ 
                ctf_array_text(char, arrfield2, text, 10)
 
@@ -123,6 +124,11 @@ TRACEPOINT_EVENT(
                 * ctf_sequence: a dynamically-sized array.
                 * args: (type, field name, argument expression,
                 *      type of length expression, length expression)
+                * The "type of length expression" needs to be an
+                * unsigned type. As a reminder, "unsigned char" should
+                * be preferred to "char", since the signedness of
+                * "char" is implementation-defined.
+                * Behavior is undefined if "text" field is NULL.
                 */ 
                ctf_sequence(char, seqfield1, text,
                             size_t, textlen)
@@ -130,6 +136,7 @@ TRACEPOINT_EVENT(
                /*
                 * ctf_sequence_text: a dynamically-sized array, printed
                 * as string. No need to be null-terminated.
+                * Behavior is undefined if "text" field is NULL.
                 */
                ctf_sequence_text(char, seqfield2, text,
                             size_t, textlen)
@@ -137,6 +144,7 @@ TRACEPOINT_EVENT(
                /*
                 * ctf_string: null-terminated string.
                 * args: (field name, argument expression)
+                * Behavior is undefined if "text" field is NULL.
                 */
                ctf_string(stringfield, text)
 
@@ -238,6 +246,10 @@ For instance, add within a function:
 As a call to the tracepoint. It will only be activated when requested by
 lttng(1) through lttng-sessiond(8).
 
+Even though LTTng-UST supports tracepoint() call site duplicates having
+the same provider and event name, it is recommended to use a
+provider event name pair only once within the source code to help
+mapping events back to their call sites when analyzing the trace.
 .fi
 
 .SH "BUILDING/LINKING THE TRACEPOINT PROVIDER"
@@ -257,11 +269,11 @@ carefully:
     - If building the provider directly into the application,
       link the application with "\-llttng-ust".
     - If building a static library for the provider, link the static
-      library with "\-lllttng-ust".
+      library with "\-llttng-ust".
     - Include the tracepoint provider header into all C files using
       the provider.
     - Example:
-        tests/hello/  hello.c tp.c ust_tests_hello.h Makefile.example
+      - tests/hello/  hello.c tp.c ust_tests_hello.h Makefile.example
 
   2) Compile the Tracepoint Provider separately from the application,
      using dynamic linking:
@@ -276,15 +288,15 @@ carefully:
     - Link application with "\-ldl".
     - Set a LD_PRELOAD environment to preload the tracepoint provider
       shared object before starting the application when tracing is
-      needed.
+      needed. Another way is to dlopen the tracepoint probe when needed
+      by the application.
     - Example:
-      - tests/demo/   demo.c  tp*.c ust_tests_demo*.h demo-trace
+      - doc/examples/demo   demo.c  tp*.c ust_tests_demo*.h demo-trace
 
-  - Note about dlopen() usage: due to locking side-effects due to the
-    way libc lazily resolves Thread-Local Storage (TLS) symbols when a
-    library is dlopen'd, linking the tracepoint probe or liblttng-ust
-    with dlopen() is discouraged. They should be linked with the
-    application using "\-llibname" or loaded with LD_PRELOAD.
+  - Note about dlclose() usage: it is not safe to use dlclose on a
+    provider shared object that is being actively used for tracing due
+    to a lack of reference counting from lttng-ust to the used shared
+    object.
   - Enable instrumentation and control tracing with the "lttng" command
     from lttng-tools. See lttng-tools doc/quickstart.txt.
   - Note for C++ support: although an application instrumented with
@@ -304,6 +316,38 @@ LD_PRELOAD=liblttng-ust-fork.so appname).
 
 .fi
 
+.SH "CONTEXT"
+
+.PP
+Context information can be prepended by the tracer before each, or some,
+events. The following context information is supported by LTTng-UST:
+.PP
+
+.PP
+.IP "vtid"
+Virtual thread ID: thread ID as seen from the point of view of the
+process namespace.
+.PP
+
+.PP
+.IP "vpid"
+Virtual process ID: process ID as seen from the point of view of the
+process namespace.
+.PP
+
+.PP
+.IP "procname"
+Thread name, as set by exec() or prctl(). It is recommended that
+programs set their thread name with prctl() before hitting the first
+tracepoint for that thread.
+.PP
+
+.PP
+.IP "pthread_id"
+Pthread identifier. Can be used on architectures where pthread_t maps
+nicely to an unsigned long type.
+.PP
+
 .SH "ENVIRONMENT VARIABLES"
 
 .PP
@@ -324,12 +368,13 @@ startup time.
 .SH "SEE ALSO"
 
 .PP
-lttng-gen-tp(1), lttng(1), babeltrace(1), lttng-sessiond(8)
+lttng-gen-tp(1), lttng(1), babeltrace(1), lttng-ust-cyg-profile(3),
+lttng-sessiond(8)
 .PP
 .SH "BUGS"
 
 .PP
-No knows bugs at this point.
+No known bugs at this point.
 
 If you encounter any issues or usability problem, please report it on
 our mailing list <lttng-dev@lists.lttng.org> to help improve this