| 1 | LTTng-UST |
| 2 | ========= |
| 3 | |
| 4 | The LTTng User Space Tracing (LTTng-UST) library allows any C/C++ |
| 5 | application to be instrumented for and traced by |
| 6 | [LTTng](http://lttng.org/). LTTng-UST also includes a logging |
| 7 | back-end for Java applications and various dynamically loadable |
| 8 | user space tracing helpers for any application. |
| 9 | |
| 10 | |
| 11 | Prerequisites |
| 12 | ------------- |
| 13 | |
| 14 | LTTng-UST depends on [liburcu](http://liburcu.org/) v0.7.2 at build and |
| 15 | run times. |
| 16 | |
| 17 | |
| 18 | Building |
| 19 | -------- |
| 20 | |
| 21 | ### Prerequisites |
| 22 | |
| 23 | This source tree is based on the Autotools suite from GNU to simplify |
| 24 | portability. Here are some things you should have on your system in order to |
| 25 | compile the Git repository tree: |
| 26 | |
| 27 | - GNU Autotools (Automake >= 1.10, Autoconf >= 2.50, Autoheader >= 2.50; |
| 28 | make sure your system-wide `automake` points to a recent version!) |
| 29 | - [GNU Libtool](http://www.gnu.org/software/autoconf/) >= 2.2 |
| 30 | - Perl (optional: needed for `make check` and tests) |
| 31 | |
| 32 | If you get the tree from the Git repository, you will need to run |
| 33 | |
| 34 | ./bootstrap |
| 35 | |
| 36 | in its root. It calls all the GNU tools needed to prepare the tree |
| 37 | configuration. |
| 38 | |
| 39 | To build LTTng-UST, do: |
| 40 | |
| 41 | ./configure |
| 42 | make |
| 43 | sudo make install |
| 44 | sudo ldconfig |
| 45 | |
| 46 | **Note:** the `configure` script sets `/usr/local` as the default prefix for |
| 47 | files it installs. However, this path is not part of most distributions' |
| 48 | default library path, which will cause builds depending on `liblttng-ust` |
| 49 | to fail unless `-L/usr/local/lib` is added to `LDFLAGS`. You may provide a |
| 50 | custom prefix to `configure` by using the `--prefix` switch |
| 51 | (e.g., `--prefix=/usr`). LTTng-UST needs to be a shared library, _even if_ |
| 52 | the tracepoint probe provider is statically linked into the application. |
| 53 | |
| 54 | |
| 55 | Using |
| 56 | ----- |
| 57 | |
| 58 | First of all, create an instrumentation header following the |
| 59 | [tracepoint examples](doc/examples). |
| 60 | |
| 61 | There are two ways to compile the tracepoint provider and link it with |
| 62 | your application: statically or dynamically. Please follow carefully one |
| 63 | or the other method. |
| 64 | |
| 65 | |
| 66 | ### Static linking |
| 67 | |
| 68 | This method links the tracepoint provider with the application, |
| 69 | either directly or through a static library (`.a`): |
| 70 | |
| 71 | 1. Into exactly one unit (C/C++ source file) of your _application_, |
| 72 | define `TRACEPOINT_DEFINE` and include the tracepoint provider |
| 73 | header. |
| 74 | 2. Include the tracepoint provider header into all C/C++ files using |
| 75 | the provider and insert tracepoints using the `tracepoint()` macro. |
| 76 | 3. Use `-I.` when compiling the unit defining `TRACEPOINT_DEFINE` |
| 77 | (e.g., `tp.c`). |
| 78 | 4. Link the application with `-ldl` on Linux, or with `-lc` on BSD, |
| 79 | and with `-llttng-ust`. |
| 80 | |
| 81 | Example: |
| 82 | |
| 83 | gcc -c -I. tp.c |
| 84 | gcc -c some-source.c |
| 85 | gcc -c other-source.c |
| 86 | gcc -o my-app tp.o some-source.o other-source.o -ldl -llttng-ust |
| 87 | |
| 88 | Run the application directly: |
| 89 | |
| 90 | ./my-app |
| 91 | |
| 92 | Other relevant examples: |
| 93 | |
| 94 | - [`doc/examples/easy-ust`](doc/examples/easy-ust) |
| 95 | - [`doc/examples/hello-static-lib`](doc/examples/hello-static-lib) |
| 96 | |
| 97 | |
| 98 | ### Dynamic loading |
| 99 | |
| 100 | This method decouples the tracepoint provider from the application, |
| 101 | making it dynamically loadable. |
| 102 | |
| 103 | 1. Into exactly one unit of your _application_, define |
| 104 | `TRACEPOINT_DEFINE` _and_ `TRACEPOINT_PROBE_DYNAMIC_LINKAGE`, |
| 105 | then include the tracepoint provider header. |
| 106 | 2. Include the tracepoint provider header into all C/C++ files using |
| 107 | the provider and insert tracepoints using the `tracepoint()` macro. |
| 108 | 3. Use `-I.` and `-fpic` when compiling the tracepoint provider |
| 109 | (e.g., `tp.c`). |
| 110 | 4. Link the tracepoint provider with `-llttng-ust` and make it a |
| 111 | shared object with `-shared`. |
| 112 | 5. Link the application with `-ldl` on Linux, or with `-lc` on BSD. |
| 113 | |
| 114 | Example: |
| 115 | |
| 116 | gcc -c -I. -fpic tp.c |
| 117 | gcc -o tp.so -shared tp.o -llttng-ust |
| 118 | gcc -o my-app some-source.c other-source.c -ldl |
| 119 | |
| 120 | To run _without_ LTTng-UST support: |
| 121 | |
| 122 | ./my-app |
| 123 | |
| 124 | To run with LTTng-UST support (register your tracepoint provider, |
| 125 | `tp.so`): |
| 126 | |
| 127 | LD_PRELOAD=./tp.so ./my-app |
| 128 | |
| 129 | You could also use `libdl` directly in your application and `dlopen()` |
| 130 | your tracepoint provider shared object (`tp.so`) to make LTTng-UST |
| 131 | tracing possible. |
| 132 | |
| 133 | Other relevant examples: |
| 134 | |
| 135 | - [`doc/examples/demo`](doc/examples/demo) |
| 136 | |
| 137 | |
| 138 | ### Controlling tracing and viewing traces |
| 139 | |
| 140 | Use [LTTng-tools](https://lttng.org/download) to control the tracer. |
| 141 | Use [Babeltrace](https://lttng.org/babeltrace) to print traces as a |
| 142 | human-readable text log. |
| 143 | |
| 144 | |
| 145 | ### Environment variables and compile flags |
| 146 | |
| 147 | - `liblttng-ust` debug can be activated by setting the environment |
| 148 | variable `LTTNG_UST_DEBUG` when launching the user application. It |
| 149 | can also be enabled at build time by compiling LTTng-UST with |
| 150 | `-DLTTNG_UST_DEBUG`. |
| 151 | - The environment variable `LTTNG_UST_REGISTER_TIMEOUT` can be used to |
| 152 | specify how long the applications should wait for the session |
| 153 | daemon _registration done_ command before proceeding to execute the |
| 154 | main program. The default is 3000 ms (3 seconds). The timeout value |
| 155 | is specified in milliseconds. The value 0 means _don't wait_. The |
| 156 | value -1 means _wait forever_. Setting this environment variable to 0 |
| 157 | is recommended for applications with time constraints on the process |
| 158 | startup time. |
| 159 | - The compilation flag `-DLTTNG_UST_DEBUG_VALGRIND` should be enabled |
| 160 | at build time to allow `liblttng-ust` to be used with Valgrind |
| 161 | (side-effect: disables per-CPU buffering). |
| 162 | |
| 163 | |
| 164 | ### Notes |
| 165 | |
| 166 | #### C++ support |
| 167 | |
| 168 | Since LTTng-UST 2.3, both tracepoints and tracepoint providers can be |
| 169 | compiled in C++. To compile tracepoint probes in C++, you need |
| 170 | G++ >= 4.7 or Clang. |
| 171 | |
| 172 | |
| 173 | Contact |
| 174 | ------- |
| 175 | |
| 176 | Maintainer: [Mathieu Desnoyers](mailto:mathieu.desnoyers@efficios.com) |
| 177 | |
| 178 | Mailing list: [`lttng-dev@lists.lttng.org`](https://lttng.org/cgi-bin/mailman/listinfo/lttng-dev) |
| 179 | |
| 180 | |
| 181 | Package contents |
| 182 | ---------------- |
| 183 | |
| 184 | This package contains the following elements: |
| 185 | |
| 186 | - `doc`: LTTng-UST documentation and examples. |
| 187 | - `include`: the public header files that will be installed on the |
| 188 | system. |
| 189 | - `liblttng-ust`: the actual userspace tracing library that must be |
| 190 | linked to the instrumented programs. |
| 191 | - `liblttng-ust-comm`: a static library shared between `liblttng-ust` |
| 192 | and LTTng-tools, that provides functions that allow these components |
| 193 | to communicate together. |
| 194 | - `liblttng-ust-ctl`: a library to control tracing in other processes; |
| 195 | used by LTTng-tools. |
| 196 | - `liblttng-ust-cyg-profile`: a library that can be preloaded (using |
| 197 | `LD_PRELOAD`) to instrument function entries and exits when the target |
| 198 | application is built with the GCC flag `-finstrument-functions`. |
| 199 | - `liblttng-ust-dl`: a library that can be preloaded to instrument |
| 200 | calls to `dlopen()` and `dlclose()`. |
| 201 | - `liblttng-ust-fork`: a library that is preloaded and that hijacks |
| 202 | calls to several system calls in order to trace across these calls. |
| 203 | It _has_ to be preloaded in order to hijack calls. In contrast, |
| 204 | `liblttng-ust` may be linked at build time. |
| 205 | - `liblttng-ust-java`: a simple library that uses JNI to allow tracing |
| 206 | in Java programs. |
| 207 | - `liblttng-ust-jul`: a package that includes a JNI library and a JAR |
| 208 | library to provide an LTTng-UST logging back-end for Java application |
| 209 | using Java Util Logging. |
| 210 | - `liblttng-ust-libc-wrapper`: an example library that can be |
| 211 | preloaded to instrument some calls to libc (currently `malloc()` and |
| 212 | `free()`) and to POSIX threads (mutexes currently instrumented) in |
| 213 | any program without need to recompile it. |
| 214 | - `libringbuffer`: the ring buffer implementation used within LTTng-UST. |
| 215 | - `snprintf`: an asynchronous signal-safe version of `snprintf()`. |
| 216 | - `tests`: various test programs. |
| 217 | - `tools`: home of `lttng-gen-tp`. |