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