1 <html>
2 <head> <title>JVM TI Demonstration Code</title> </head>
3
4 <h1>JVM TI Demonstration Code</h1>
5
6 <p>
7 The
8 Java<sup><font size=-2>TM</font></sup> Virtual Machine Tools Interface (JVM TI)
9 is a native tool interface provided in JDK 5.0 and newer.
10 Native libraries that use JVM TI and are loaded into the
11 Java Virtual Machine
12 via the -agentlib, -agentpath, or -Xrun (deprecated) interfaces, are
13 called Agents.
14 <p>
15 <A HREF="http://java.sun.com/j2se/latest/docs/guide/jvmti">JVM TI</A>
16 was designed to work with the
17 Java Native Interface
18 (<A HREF="http://java.sun.com/j2se/latest/docs/guide/jni">JNI</A>),
19 and eventually displace the
20 Java Virtual Machine Debugging Interface
21 (<A HREF="http://java.sun.com/j2se/1.5.0/docs/guide/jpda/jvmdi-spec.html">JVMDI</A>)
22 and the
23 Java Virtual Machine Profiling Interface
24 (<A HREF="http://java.sun.com/j2se/1.5.0/docs/guide/jvmpi/index.html">JVMPI</A>).
25
26 <p>
27 We have created a set of demonstration agents that should
28 help show many of the features and abilities of the
29 interface. This list of demonstration agents will change over time.
30 They are provided as educational tools and as starting
31 points for Java tool development.
32
33 <p>
34 These agents are built with every JDK build and some basic testing is performed
35 on a regular basis, but no extensive testbases currently
36 exist for these agents.
37 Every JDK installation should include all the pre-built binaries and sources for
38 all these agents, just look in the demo/jvmti directory of your JDK.
39
40
41 <h2>Using or Running These Agents</h2>
42
43 <p>
44 Using these agents will require the VM to locate the shared library file
45 before any actual Java code is run.
46 The JDK installation should contain all the agent libraries in
47 the ${JAVA_HOME}/demo/jvmti/<i>agent-name</i>/lib directories.
48 The Solaris 64bit version would be contained in the sparcv9 or amd64
49 subdirectory.
50 If 'java' complains that it can't find the library,
51 you may need to add the directory containing the library into the
52 LD_LIBRARY_PATH environment variable (Unix), or the PATH environment
53 variable (Windows).
54 This is system and platform specific.
55 If you are using 64bit Solaris (e.g. 'java -d64'),
56 you should use LD_LIBRARY_PATH64.
57 Some agents such as hprof (heap/cpu profiler) and jdwp (debugger backend)
58 are located inside the primary JDK directories and will always be found
59 in those locations.
60
61 <p>
62 The agents that instrument classfiles
63 (i.e. BCI, usually through the java_crw_demo library)
64 such as hprof, heapTracker, mtrace, and minst,
65 also need to have the Java classes they use available in the bootclasspath.
66 The one used by hprof is already in the bootclasspath, and the
67 other agents will make attempts at automatically adding their jar file
68 (e.g. heapTracker.jar, mtrace.jar, or minst.jar) to the bootclasspath
69 with AddToBootstrapClassLoaderSearch from JVM TI at startup
70 (see the agent_util code).
71 This is done by locating this jar file at
72 ${JAVA_HOME}/demo/jvmti/<i>agent-name</i>
73 where JAVA_HOME is obtained by calling GetSystemProperty from JVM TI
74 with "java.home".
75 We recognize that this is not ideal, but felt that as just demonstration
76 code it was acceptable.
77 Ideally the agent could find out the actual directory it came from and
78 locate the jar file relative to that location.
79 Our demonstration agents currently do not do this.
80
81 <p>
82 If you choose to modify or change these agents, the above information
83 is important in making everything is found.
84 It is recommended that you change the name of the agent when you
85 modify it to avoid conflicts with the existing demo agents.
86 Or better yet, go to http://jdk.dev.java.net and submit your
87 changes to the agent as an RFE to the JDK.
88
89
90 <h2> Demonstration Agents Available </h2>
91
92 <ul>
93
94 <li>
95 <A HREF="versionCheck">versionCheck</A>
96 <br>
97 This is a extremely small agent that does nothing but check the
98 version string supplied in the jvmti.h file, with the version
99 number supplied by the VM at runtime.
100 </li>
101
102 <li>
103 <A HREF="mtrace">mtrace</A>
104 <br>
105 This is a small agent that does method tracing.
106 It uses Bytecode Instrumentation (BCI) via the java_crw_demo library.
107 </li>
108
109 <li>
110 <A HREF="minst">minst</A>
111 <br>
112 This is an even smaller agent that does just method entry tracing.
113 It also uses Bytecode Instrumentation (BCI) via the java_crw_demo library,
114 but the instrumentation code is pure Java (no Java native methods used).
115 NOTE: Be sure to check out java.lang.instrument for a way to avoid
116 native code agents completely.
117 </li>
118
119 <li>
120 <A HREF="gctest">gctest</A>
121 <br>
122 This is a small agent that does garbage collection counting.
123 </li>
124
125 <li>
126 <A HREF="heapViewer">heapViewer</A>
127 <br>
128 This is a small agent that does some basic heap inspections.
129 </li>
130
131 <li>
132 <A HREF="heapTracker">heapTracker</A>
133 <br>
134 This is a small agent that does BCI to capture object creation
135 and track them.
136 It uses Bytecode Instrumentation (BCI) via the java_crw_demo library.
137 </li>
138
139 <li>
140 <A HREF="waiters">waiters</A>
141 <br>
142 This is a small agent that gets information about threads
143 waiting on monitors.
144 </li>
145
146 <li>
147 <A HREF="hprof">hprof</A>
148 <br>
149 This is a large agent that does heap and cpu profiling.
150 This demo agent is actually built into the
151
152 Java Runtime Environment (JRE).
153 It uses Bytecode Instrumentation (BCI) via the java_crw_demo library.
154 <br>
155 <b>Note:</b> hprof is NOT a small or simple agent, the other smaller demos
156 should be looked at first.
157 </li>
158
159 </ul>
160
161
162
163 <h2>Agent Support</h2>
164
165 <ul>
166
167 <li>
168 <A HREF="java_crw_demo">java_crw_demo</A>
169 <br>
170 This is a demo C library that does class file to class file
171 transformations or BCI (Bytecode Instrumentation).
172 It is used by several of the above agents.
173 </li>
174
175
176 </ul>
177
178
179
180 <h2>Native Library Build Hints</h2>
181
182 <p>
183 All libraries loaded into java are assumed to be MT-safe (Multi-thread safe).
184 This means that multiple threads could be executing the code at the same
185 time, and static or global data may need to be placed in critical
186 sections. See the Raw Monitor interfaces for more information.
187
188 <p>
189 All native libraries loaded into the
190 Java Virtual Machine,
191 including Agent libraries,
192 need to be compiled and built in a compatible way.
193 Certain native compilation options or optimizations should be avoided,
194 and some are required.
195 More information on this options is available in the man pages for
196 the various compilers.
197
198 <p>
199 Some native compiler and linker options can create fatal or
200 erroneous behavior when native agent libraries are operating
201 inside the Java Virtual Machine.
202 It would take too many words to describe all the possible issues with all
203 the native compiler options, optimizations, and settings.
204 Here are some recommendations on the basic compiler and linker options
205 we recommend:
206
207 <ul>
208
209 <h3> Solaris </h3>
210
211 <li>
212 On Solaris, using the Sun Studio 11 C compiler,
213 the typical compile and link command lines might look something like:
214 <br>
215 For 32bit SPARC:
216 <br>
217 <code><ul>
218 cc -xO2 -mt -xregs=no%appl -xmemalign=4s -xarch=v8 -KPIC -c <i>*.c</i>
219 <br>
220 cc -mt -xarch=v8 -z defs -ztext -G -o <i>libXXX.so *.o</i> -lc
221 </code></ul>
222 <br>
223 For 64bit SPARC:
224 <br>
225 <code><ul>
226 cc -xO2 -mt -xregs=no%appl -xarch=v9 -KPIC -c <i>*.c</i>
227 <br>
228 cc -mt -xarch=v9 -z defs -ztext -G -o <i>libXXX.so *.o</i> -lc
229 </code></ul>
230 <br>
231 For X86:
232 <br>
233 <code><ul>
234 cc -xO2 -mt -xregs=no%frameptr -KPIC -c <i>*.c</i>
235 <br>
236 cc -mt -z defs -ztext -G -o <i>libXXX.so *.o</i> -lc
237 </code></ul>
238 <br>
239 For AMD64:
240 <br>
241 <code><ul>
242 cc -xO2 -mt -xregs=no%frameptr -xarch=amd64 -KPIC -c <i>*.c</i>
243 <br>
244 cc -mt -xarch=amd64 -z defs -ztext -G -o <i>libXXX.so *.o</i> -lc
245 </code></ul>
246 <br>
247 </li>
248
249 <li>
250 Architecture/File Format:
251 For SPARC 32bit use <code>-xarch=v8</code>,
252 for SPARC 64bit use <code>-xarch=v9</code>,
253 for X86 (32-bit)
254 <i>
255 leave the option off or use <code>-xarch=generic</code>
256 </i>,
257 and for AMD64 (64bit) use <code>-xarch=amd64</code>
258 with both C and C++.
259 <br>
260 This is to be specific as to the architecture and the file format
261 of the .o files (and ultimately of the .so).
262 </li>
263
264 <li>
265 MT-Safe, Position Independent: Use <code>-KPIC -mt</code>
266 with both C and C++.
267 </li>
268
269 <li>
270 Register usage: For SPARC (both 32bit and 64bit) use
271 <code>-xregs=no%appl</code> and for X86 and AMD64 use <code>-xregs=no%frameptr</code>
272 with both C and C++.
273 </li>
274
275 <li>
276 Alignment: For SPARC 32bit use -xmemalign=4s and for SPARC 64bit do NOT use <code>-xmemalign=4</code>
277 with both C and C++.
278 </li>
279
280 <li>
281 Dependencies: Use <code>ldd -r <i>LibraryName</i></code>.
282 <br>
283 After the shared library has been built, the utility
284 <code>ldd</code> can be used to verify that all dependent libraries
285 have been satisfied, and all externs can be found.
286 If <code>ldd</code> says anything is missing, it is very likely that the JVM will also
287 be unable to load this library.
288 This usually means that you missed some <code>-l<i>name</i></code>
289 options when building the library, or perhaps forgot a <code>-R path</code>
290 option that tells the library where to look for libraries at runtime.
291 </li>
292
293 <h3> Linux </h3>
294
295 <li>
296 On Linux, using the gcc version 3.2,
297 the typical compile and link command lines might look something like:
298 <br>
299 For X86:
300 <br>
301 <code><ul>
302 gcc -O2 -fPIC -pthread -DLINUX -c <i>*.c</i>
303 <br>
304 gcc -z defs -static-libgcc -shared -mimpure-text -o <i>libXXX.so *.o</i> -lc
305 </code></ul>
306 <br>
307 For AMD64:
308 <br>
309 <code><ul>
310 gcc -O2 -fPIC -pthread -DLINUX -D_LP64=1 -c <i>*.c</i>
311 <br>
312 gcc -z defs -static-libgcc -shared -mimpure-text -o <i>libXXX.so *.o</i> -lc
313 </code></ul>
314 <br>
315 </li>
316
317 <li>
318 MT-Safe, Position Independent:
319 Use <code>-fPIC -pthread</code>.
320 </li>
321
322 <li>
323 Agent Demo Code: Needs -DLINUX
324 </li>
325
326 <li>
327 Register Usage: Use <code>-fno-omit-frame-pointer</code>.
328 <br>
329 It is important that these libraries have frame pointer register usage, see the above comments on the Solaris
330 <code>-xregs=no%frameptr</code>
331 option.
332 </li>
333
334 <li>
335 Library: Use -static-libgcc -mimpure-text.
336 <br>
337 When building the shared library (-shared option), this option
338 allows for maximum portability of the library between different
339 flavors of Linux.
340 The problem we have seen with Linux is that we cannot depend
341 on a compatible shared gcc library existing on all the versions of
342 Linux we can run on.
343 By doing this static link, the version script becomes more
344 important, making sure you don't expose any extern symbols
345 you didn't intend to.
346 </li>
347
348 <li>
349 Dependencies: Use <code>ldd -r <i>LibraryName</i></code>.
350 <br>
351 Provides the same checking as Solaris (see above).
352 </li>
353
354 <h3> Windows </h3>
355
356 <li>
357 On Windows and using the Microsoft C++ Compiler Visual Studio .NET 2003,
358 the typical compile and link command lines might look something like:
359 <br>
360 For X86:
361 <br>
362 <code><ul>
363 cl /O1 /MD /D _STATIC_CPPLIB /c <i>*.c</i>
364 <br>
365 link /dll /opt:REF /out:<i>XXX.dll *.obj</i>
366 </code></ul>
367 <br>
368 For AMD64:
369 <br>
370 <code><ul>
371 cl /O1 /MD /D _STATIC_CPPLIB /c <i>*.c</i>
372 <br>
373 link /dll /opt:REF /out:<i>XXX.dll *.obj</i>
374 </code></ul>
375 <br>
376 </li>
377
378 <li>
379 Library: Use <code>/opt:REF </code> when building the dll.
380 </li>
381
382 <li>
383 MS DLL Runtime: Use the <code>/MD /D _STATIC_CPPLIB</code> option.
384 <br>
385 This causes your dll to become dependent on MSVCRT.DLL and/or
386 the newer C++ runtime MSVCR71.DLL.
387 The option /D _STATIC_CPPLIB prevents you from becoming dependent on the
388 C++ library MSVCP71.DLL.
389 This is what we use in the JDK, but there are probably many combinations
390 that you could safely use, unfortunately there are many combinations
391 of runtimes that will not work.
392 Check the Microsoft site on proper use of runtimes.
393 </li>
394
395 <li>
396 Dependencies: Use VC++ <code>dumpbin /exports</code> and the VC++ "Dependency Walker".
397 <br>
398 Provides dependency information similar to <code>ldd</code>.
399 </li>
400
401 </ul>
402
403
404 <h2>For More Information</h2>
405
406 <p>
407 Remember, the complete source to all these agents is contained in the JDK
408 installations at demo/jvmti.
409
410 <p>
411 For more detailed information on JVM TI, refer to
412 <A HREF="http://java.sun.com/j2se/latest/docs/guide/jvmti">
413 http://java.sun.com/j2se/latest/docs/guide/jvmti.</A>
414
415 <p>
416 More information on using JNI and building native libraries refer to:
417 <A HREF="http://java.sun.com/j2se/latest/docs/guide/jni">
418 http://java.sun.com/j2se/latest/docs/guide/jni</A>.
419
420 <p>
421 Additional information can also be found by doing a search on "jvmti" at
422 <A HREF="http://java.sun.com/j2se">http://java.sun.com/j2se</A>.
423 Various technical articles are also available through this website.
424 And don't forget the
425 Java Tutorials at
426 <A HREF="http://java.sun.com/docs/books/tutorial">http://java.sun.com/docs/books/tutorial</A>
427 for getting a quick start on all the various interfaces.
428
429 <h2>Comments and Feedback</h2>
430
431 <p>
432 Comments regarding JVM TI or on any of these demonstrations should be
433 sent through
434 <A HREF="http://java.sun.com/mail">http://java.sun.com/mail/</A>
435
436
437
438 </html>