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1 /*
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2 * Copyright 2001-2006 Sun Microsystems, Inc. All Rights Reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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20 * CA 95054 USA or visit www.sun.com if you need additional information or
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21 * have any questions.
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22 *
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23 */
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24
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25 package sun.jvm.hotspot.runtime.x86;
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26
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27 import sun.jvm.hotspot.debugger.*;
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28 import sun.jvm.hotspot.debugger.x86.*;
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29 import sun.jvm.hotspot.code.*;
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30 import sun.jvm.hotspot.interpreter.*;
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31 import sun.jvm.hotspot.runtime.*;
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32
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33 /** <P> Should be able to be used on all x86 platforms we support
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34 (Win32, Solaris/x86, and soon Linux) to implement JavaThread's
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35 "currentFrameGuess()" functionality. Input is an X86ThreadContext;
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36 output is SP, FP, and PC for an X86Frame. Instantiation of the
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37 X86Frame is left to the caller, since we may need to subclass
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38 X86Frame to support signal handler frames on Unix platforms. </P>
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39
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40 <P> Algorithm is to walk up the stack within a given range (say,
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41 512K at most) looking for a plausible PC and SP for a Java frame,
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42 also considering those coming in from the context. If we find a PC
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43 that belongs to the VM (i.e., in generated code like the
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44 interpreter or CodeCache) then we try to find an associated EBP.
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45 We repeat this until we either find a complete frame or run out of
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46 stack to look at. </P> */
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47
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48 public class X86CurrentFrameGuess {
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49 private X86ThreadContext context;
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50 private JavaThread thread;
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51 private Address spFound;
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52 private Address fpFound;
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53 private Address pcFound;
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54
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55 private static final boolean DEBUG = System.getProperty("sun.jvm.hotspot.runtime.x86.X86Frame.DEBUG")
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56 != null;
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57
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58 public X86CurrentFrameGuess(X86ThreadContext context,
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59 JavaThread thread) {
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60 this.context = context;
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61 this.thread = thread;
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62 }
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63
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64 /** Returns false if not able to find a frame within a reasonable range. */
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65 public boolean run(long regionInBytesToSearch) {
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66 Address sp = context.getRegisterAsAddress(X86ThreadContext.SP);
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67 Address pc = context.getRegisterAsAddress(X86ThreadContext.PC);
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68 Address fp = context.getRegisterAsAddress(X86ThreadContext.FP);
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69 if (sp == null) {
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70 // Bail out if no last java frame eithe
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71 if (thread.getLastJavaSP() != null) {
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72 setValues(thread.getLastJavaSP(), thread.getLastJavaFP(), null);
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73 return true;
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74 }
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75 // Bail out
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76 return false;
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77 }
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78 Address end = sp.addOffsetTo(regionInBytesToSearch);
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79 VM vm = VM.getVM();
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80
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81 setValues(null, null, null); // Assume we're not going to find anything
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82
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83 if (vm.isJavaPCDbg(pc)) {
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84 if (vm.isClientCompiler()) {
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85 // If the topmost frame is a Java frame, we are (pretty much)
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86 // guaranteed to have a viable EBP. We should be more robust
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87 // than this (we have the potential for losing entire threads'
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88 // stack traces) but need to see how much work we really have
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89 // to do here. Searching the stack for an (SP, FP) pair is
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90 // hard since it's easy to misinterpret inter-frame stack
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91 // pointers as base-of-frame pointers; we also don't know the
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92 // sizes of C1 frames (not registered in the nmethod) so can't
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93 // derive them from ESP.
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94
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95 setValues(sp, fp, pc);
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96 return true;
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97 } else {
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98 if (vm.getInterpreter().contains(pc)) {
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99 if (DEBUG) {
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100 System.out.println("CurrentFrameGuess: choosing interpreter frame: sp = " +
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101 sp + ", fp = " + fp + ", pc = " + pc);
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102 }
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103 setValues(sp, fp, pc);
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104 return true;
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105 }
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106
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107 // For the server compiler, EBP is not guaranteed to be valid
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108 // for compiled code. In addition, an earlier attempt at a
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109 // non-searching algorithm (see below) failed because the
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110 // stack pointer from the thread context was pointing
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111 // (considerably) beyond the ostensible end of the stack, into
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112 // garbage; walking from the topmost frame back caused a crash.
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113 //
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114 // This algorithm takes the current PC as a given and tries to
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115 // find the correct corresponding SP by walking up the stack
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116 // and repeatedly performing stackwalks (very inefficient).
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117 //
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118 // FIXME: there is something wrong with stackwalking across
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119 // adapter frames...this is likely to be the root cause of the
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120 // failure with the simpler algorithm below.
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121
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122 for (long offset = 0;
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123 offset < regionInBytesToSearch;
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124 offset += vm.getAddressSize()) {
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125 try {
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126 Address curSP = sp.addOffsetTo(offset);
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127 Frame frame = new X86Frame(curSP, null, pc);
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128 RegisterMap map = thread.newRegisterMap(false);
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129 while (frame != null) {
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130 if (frame.isEntryFrame() && frame.entryFrameIsFirst()) {
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131 // We were able to traverse all the way to the
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132 // bottommost Java frame.
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133 // This sp looks good. Keep it.
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134 if (DEBUG) {
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135 System.out.println("CurrentFrameGuess: Choosing sp = " + curSP + ", pc = " + pc);
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136 }
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137 setValues(curSP, null, pc);
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138 return true;
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139 }
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140 frame = frame.sender(map);
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141 }
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142 } catch (Exception e) {
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143 if (DEBUG) {
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144 System.out.println("CurrentFrameGuess: Exception " + e + " at offset " + offset);
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145 }
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146 // Bad SP. Try another.
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147 }
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148 }
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149
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150 // Were not able to find a plausible SP to go with this PC.
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151 // Bail out.
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152 return false;
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153
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154 /*
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155 // Original algorithm which does not work because SP was
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156 // pointing beyond where it should have:
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157
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158 // For the server compiler, EBP is not guaranteed to be valid
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159 // for compiled code. We see whether the PC is in the
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160 // interpreter and take care of that, otherwise we run code
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161 // (unfortunately) duplicated from X86Frame.senderForCompiledFrame.
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162
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163 CodeCache cc = vm.getCodeCache();
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164 if (cc.contains(pc)) {
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165 CodeBlob cb = cc.findBlob(pc);
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166
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167 // See if we can derive a frame pointer from SP and PC
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168 // NOTE: This is the code duplicated from X86Frame
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169 Address saved_fp = null;
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170 int llink_offset = cb.getLinkOffset();
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171 if (llink_offset >= 0) {
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172 // Restore base-pointer, since next frame might be an interpreter frame.
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173 Address fp_addr = sp.addOffsetTo(VM.getVM().getAddressSize() * llink_offset);
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174 saved_fp = fp_addr.getAddressAt(0);
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175 }
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176
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177 setValues(sp, saved_fp, pc);
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178 return true;
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179 }
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180 */
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181 }
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182 } else {
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183 // If the current program counter was not known to us as a Java
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184 // PC, we currently assume that we are in the run-time system
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185 // and attempt to look to thread-local storage for saved ESP and
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186 // EBP. Note that if these are null (because we were, in fact,
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187 // in Java code, i.e., vtable stubs or similar, and the SA
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188 // didn't have enough insight into the target VM to understand
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189 // that) then we are going to lose the entire stack trace for
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190 // the thread, which is sub-optimal. FIXME.
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191
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192 if (DEBUG) {
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193 System.out.println("CurrentFrameGuess: choosing last Java frame: sp = " +
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194 thread.getLastJavaSP() + ", fp = " + thread.getLastJavaFP());
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195 }
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196 if (thread.getLastJavaSP() == null) {
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197 return false; // No known Java frames on stack
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198 }
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199 setValues(thread.getLastJavaSP(), thread.getLastJavaFP(), null);
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200 return true;
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201 }
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202 }
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203
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204 public Address getSP() { return spFound; }
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205 public Address getFP() { return fpFound; }
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206 /** May be null if getting values from thread-local storage; take
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207 care to call the correct X86Frame constructor to recover this if
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208 necessary */
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209 public Address getPC() { return pcFound; }
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210
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211 private void setValues(Address sp, Address fp, Address pc) {
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212 spFound = sp;
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213 fpFound = fp;
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214 pcFound = pc;
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215 }
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216 }
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