0
|
1 <HTML>
|
|
2
|
|
3
|
|
4 <HEAD>
|
|
5 <TITLE>
|
|
6 Using The HotSpot Serviceability Agent
|
|
7 </TITLE>
|
|
8 </HEAD>
|
|
9
|
|
10 <BODY TEXT="#000000" BGCOLOR="#FFFFFF">
|
|
11 <H1>
|
|
12 Using The HotSpot Serviceability Agent
|
|
13 </H1>
|
|
14
|
|
15 <P>
|
|
16 <H2>
|
|
17 Contents
|
|
18 </H2>
|
|
19 </P>
|
|
20
|
|
21 <UL>
|
|
22 <LI> <A HREF = "#INTRODUCTION">Introduction</A>
|
|
23 <LI> <A HREF = "#SOURCES">Organization of the sources</A>
|
|
24 <LI> <A HREF = "#RUNNING">Running HSDB</A>
|
|
25 <LI> <A HREF = "#NOTES">Notes</A>
|
|
26 </UL>
|
|
27
|
|
28 <H2>
|
|
29 <A NAME="INTRODUCTION">
|
|
30 Introduction
|
|
31 </A>
|
|
32 </H2>
|
|
33
|
|
34 <P>
|
|
35 The HotSpot Serviceability Agent (SA) is a set of Java APIs which
|
|
36 mirror the internal APIs of the HotSpot VM and which can be used to
|
|
37 examine the state of a HotSpot VM.
|
|
38 </P>
|
|
39
|
|
40 <P>
|
|
41 The system understands the layout of certain VM data structures and is
|
|
42 able to traverse these structures in an examination-only fashion; that
|
|
43 is, it does not rely on being able to run code in the target VM. For
|
|
44 this reason it transparently works with either a running VM or a core
|
|
45 file.
|
|
46 </P>
|
|
47
|
|
48 <P>
|
|
49 The system can reconstruct information about Java frames on the stack
|
|
50 and objects in the heap. Many of the important data structures in the
|
|
51 VM like the CodeCache, Universe, StubQueue, Frames, and VFrames have
|
|
52 been exposed and have relatively complete (or at least useful)
|
|
53 implementations.
|
|
54 </P>
|
|
55
|
|
56 <P>
|
|
57 A small graphical debugger called HSDB (the "HotSpot Debugger") has
|
|
58 been written using these APIs. It provides stack memory dumps
|
|
59 annotated with method invocations, compiled-code inlining (if
|
|
60 present), interpreted vs. compiled code, interpreter codelets (if
|
|
61 interpreted), and live oops from oop-map information. It also provides
|
|
62 a tree-based oop inspector. More information will be added as
|
|
63 necessary; please <A HREF = "mailto:kenneth.russell@eng">send
|
|
64 email</A> with suggestions on what would be useful.
|
|
65 </P>
|
|
66
|
|
67 <P>
|
|
68 The SA currently only works on Solaris. It uses dbx to connect to the
|
|
69 remote process or core file and communicates with a small piece of
|
|
70 code (an "import module") loaded into the debugger.
|
|
71 </P>
|
|
72
|
|
73 <H2>
|
|
74 <A NAME="SOURCES">
|
|
75 Organization of the sources
|
|
76 </A>
|
|
77 </H2>
|
|
78
|
|
79 <P>
|
|
80 The Java-side source code, which is the bulk of the SA, is in
|
|
81 src/share/vm/agent. The organization of the sun.jvm.hotspot package
|
|
82 hierarchy mirrors the organization in the VM. This should allow
|
|
83 engineers familiar with the HotSpot sources to quickly understand how
|
|
84 the SA works and to make modifications if necessary. To build these
|
|
85 sources, cd to src/share/vm/agent and type "make".
|
|
86 </P>
|
|
87
|
|
88 <P>
|
|
89
|
|
90 The SA on Solaris works by communicating with a small piece of code
|
|
91 (an "import module") loaded into dbx. The source code for this import
|
|
92 module is in src/os/solaris/agent. To build this library, cd to
|
|
93 src/os/solaris/agent and type "make 32bit" or "make 64bit". The
|
|
94 distinction is necessary because the SPARC version of dbx ships with
|
|
95 two versions of its executable, and depending on which architecture
|
|
96 (v8 or v9) the debugger is running on selects the appropriate
|
|
97 executable. The SA tries the v8 version first, but if you are running
|
|
98 on a v9 machine you must provide both versions to the SA.
|
|
99 </P>
|
|
100
|
|
101 <P>
|
|
102
|
|
103 The system is currently hardwired to look on jano for its dbx
|
|
104 executable and import module. The relevant directory structure looks
|
|
105 like this:
|
|
106
|
|
107 <UL>
|
|
108 <LI> .../hotspot/sa/
|
|
109 <UL>
|
|
110 <LI> solaris/
|
|
111 <UL>
|
|
112 <LI> sparc/
|
|
113 <UL>
|
|
114 <LI> bin/
|
|
115 <UL>
|
|
116 <LI> dbx: symlink to (v8) dbx 7.0 executable
|
|
117 </UL>
|
|
118 </UL>
|
|
119 <UL>
|
|
120 <LI> lib/
|
|
121 <UL>
|
|
122 <LI> libsvc_agent_dbx.so: 32-bit version of import module
|
|
123 </UL>
|
|
124 </UL>
|
|
125 <LI> sparcv9/
|
|
126 <UL>
|
|
127 <LI> lib/
|
|
128 <UL>
|
|
129 <LI> libsvc_agent_dbx.so: 32-bit version of import module
|
|
130 </UL>
|
|
131 </UL>
|
|
132 </UL>
|
|
133 </UL>
|
|
134 </UL>
|
|
135 </P>
|
|
136
|
|
137 <P>
|
|
138 The code which builds up path names to these executables is contained
|
|
139 in sun.jvm.hotspot.HotSpotAgent.java. There are hardcoded paths in
|
|
140 this file to jano, but the rest of the system is isolated from this.
|
|
141 </P>
|
|
142
|
|
143 <P>
|
|
144 (It would be nice to have a panel in the debugger allowing
|
|
145 configuration of all of the known operating systems' options; right
|
|
146 now Solaris is the only supported OS, making that easier.)
|
|
147 </P>
|
|
148
|
|
149 <H2>
|
|
150 <A NAME="RUNNING">
|
|
151 Running HSDB
|
|
152 </A>
|
|
153 </H2>
|
|
154
|
|
155 <P>
|
|
156 An installation of HSDB has been placed on jano. To access it, add the
|
|
157 following directory to your PATH:
|
|
158 </P>
|
|
159
|
|
160 <P>
|
|
161 <PRE>
|
|
162 /net/jano/export/disk05/hotspot/sa/bin/common
|
|
163 </PRE>
|
|
164 </P>
|
|
165
|
|
166 <P>
|
|
167 To start the debugger, type "hsdb".
|
|
168 </P>
|
|
169
|
|
170 <P>
|
|
171 Alternatively, you can start a local build of the debugger by building
|
|
172 the sources in src/share/vm/agent, cd'ing to that directory, and
|
|
173 typing "java sun.jvm.hotspot.HSDB".
|
|
174 </P>
|
|
175
|
|
176 <P>
|
|
177 There are three modes for the debugger: attaching to a local process,
|
|
178 opening a core file, and attaching to a remote "debug server". The
|
|
179 remote case requires two programs to be running on the remote machine:
|
|
180 the rmiregistry (see the script "start-rmiregistry" in this directory;
|
|
181 run this in the background) and the debug server (see the script
|
|
182 "start-debug-server"), in that order. start-rmiregistry takes no
|
|
183 arguments; start-debug-server takes as argument the process ID or the
|
|
184 executable and core file names to allow remote debugging of. Make sure
|
|
185 you do NOT have a CLASSPATH environment variable set when you run
|
|
186 these scripts. (The classes put into the rmiregistry are in sun.*, and
|
|
187 there are permissions problems if they aren't placed on the boot
|
|
188 classpath.)
|
|
189 </P>
|
|
190
|
|
191 <P>
|
|
192 NOTE that the SA currently only works against VMs on Solaris/SPARC.
|
|
193 Remote debugging of Solaris/SPARC VMs on arbitrary platforms is
|
|
194 possible using the debug server; select "Connect to debug server..."
|
|
195 in HSDB.
|
|
196 </P>
|
|
197
|
|
198 <P>
|
|
199 Once the debugger has been launched, the threads list is displayed.
|
|
200 The current set of functionality allows:
|
|
201 </P>
|
|
202
|
|
203 <UL>
|
|
204 <LI> Browsing of the annotated stack memory ("Stack Memory" button). It
|
|
205 is currently annotated with the following information:
|
|
206 <UL>
|
|
207 <LI> Method names of the Java frames and their extents (supporting
|
|
208 inlined compiled methods)
|
|
209 <LI> Locations and types of oops, found using the oop map information
|
|
210 from compiled methods (interpreter oop maps coming soon)
|
|
211 <LI> If a Java frame was interrupted by a signal (e.g., because of a
|
|
212 crash), annotates the frame with the signal name and number
|
|
213 <LI> Interpreter codelet descriptions for interpreted frames
|
|
214 </UL>
|
|
215 <LI> Finding which thread or threads caused a crash (currently
|
|
216 identified by the presence of a signal handler frame)
|
|
217 <LI> Browsing of oops using the Oop Inspector.
|
|
218 <LI> Browsing of the java.lang.Thread object's oop.
|
|
219 <LI> Object histogram and inspection of objects therein.
|
|
220 </UL>
|
|
221 </P>
|
|
222
|
|
223 <P>
|
|
224 More functionality is planned. Please <A HREF =
|
|
225 "mailto:kenneth.russell@eng">send email</A> with suggestions on what
|
|
226 would be useful, with any questions or comments, or if the debugger
|
|
227 crashes.
|
|
228 </P>
|
|
229
|
|
230 <H2>
|
|
231 <A NAME="NOTES">
|
|
232 Notes
|
|
233 </A>
|
|
234 </H2>
|
|
235
|
|
236 <P>
|
|
237 HSDB does not suspend the system at a safepoint, but at an arbitrary
|
|
238 point. This means that many of the invariants in the VM's code are not
|
|
239 followed.
|
|
240 </P>
|
|
241
|
|
242 <P>
|
|
243 As it happens, most of the places where the code ported over from the
|
|
244 VM has failed involve the topmost frame on the stack. Some
|
|
245 modifications have been made to allow the system to recognize
|
|
246 problematic situations.
|
|
247 </P>
|
|
248
|
|
249 <P>
|
|
250 Certainly, not all of the failure modes of the debugger have been
|
|
251 found. Please <A HREF = "mailto:kenneth.russell@eng">send email</A> if
|
|
252 HSDB throws an exception. The best debugging aid in these situations
|
|
253 is a core file since it is a static view of the VM to which we can
|
|
254 then adapt the debugger code, as opposed to having to try to suspend
|
|
255 the VM over and over to reproduce the failure. gcore (1) is a useful
|
|
256 tool. (NOTE: do not try gcore with any application using the DGA X
|
|
257 server extension (example: Java2Demo); the kernel will panic. See bug
|
|
258 4343237.)
|
|
259 </P>
|
|
260
|
|
261 </BODY>
|
|
262 </HTML>
|