/**
 * Should be able to be used on all amd64 platforms we support (Linux/amd64) to implement
 * JavaThread's "currentFrameGuess()" functionality. Input is an AMD64ThreadContext; output is SP,
 * FP, and PC for an AMD64Frame. Instantiation of the AMD64Frame is left to the caller, since we may
 * need to subclass AMD64Frame to support signal handler frames on Unix platforms.
 *
 * <p>Algorithm is to walk up the stack within a given range (say, 512K at most) looking for a
 * plausible PC and SP for a Java frame, also considering those coming in from the context. If we
 * find a PC that belongs to the VM (i.e., in generated code like the interpreter or CodeCache) then
 * we try to find an associated EBP. We repeat this until we either find a complete frame or run out
 * of stack to look at.
 */
public class AMD64CurrentFrameGuess {
  private AMD64ThreadContext context;
  private JavaThread thread;
  private Address spFound;
  private Address fpFound;
  private Address pcFound;

  private static final boolean DEBUG =
      System.getProperty("sun.jvm.hotspot.runtime.amd64.AMD64Frame.DEBUG") != null;

  public AMD64CurrentFrameGuess(AMD64ThreadContext context, JavaThread thread) {
    this.context = context;
    this.thread = thread;
  }

  /** Returns false if not able to find a frame within a reasonable range. */
  public boolean run(long regionInBytesToSearch) {
    Address sp = context.getRegisterAsAddress(AMD64ThreadContext.RSP);
    Address pc = context.getRegisterAsAddress(AMD64ThreadContext.RIP);
    Address fp = context.getRegisterAsAddress(AMD64ThreadContext.RBP);
    if (sp == null) {
      // Bail out if no last java frame either
      if (thread.getLastJavaSP() != null) {
        setValues(thread.getLastJavaSP(), thread.getLastJavaFP(), null);
        return true;
      }
      return false;
    }
    Address end = sp.addOffsetTo(regionInBytesToSearch);
    VM vm = VM.getVM();

    setValues(null, null, null); // Assume we're not going to find anything

    if (vm.isJavaPCDbg(pc)) {
      if (vm.isClientCompiler()) {
        // If the topmost frame is a Java frame, we are (pretty much)
        // guaranteed to have a viable EBP. We should be more robust
        // than this (we have the potential for losing entire threads'
        // stack traces) but need to see how much work we really have
        // to do here. Searching the stack for an (SP, FP) pair is
        // hard since it's easy to misinterpret inter-frame stack
        // pointers as base-of-frame pointers; we also don't know the
        // sizes of C1 frames (not registered in the nmethod) so can't
        // derive them from ESP.

        setValues(sp, fp, pc);
        return true;
      } else {
        if (vm.getInterpreter().contains(pc)) {
          if (DEBUG) {
            System.out.println(
                "CurrentFrameGuess: choosing interpreter frame: sp = "
                    + sp
                    + ", fp = "
                    + fp
                    + ", pc = "
                    + pc);
          }
          setValues(sp, fp, pc);
          return true;
        }

        // For the server compiler, EBP is not guaranteed to be valid
        // for compiled code. In addition, an earlier attempt at a
        // non-searching algorithm (see below) failed because the
        // stack pointer from the thread context was pointing
        // (considerably) beyond the ostensible end of the stack, into
        // garbage; walking from the topmost frame back caused a crash.
        //
        // This algorithm takes the current PC as a given and tries to
        // find the correct corresponding SP by walking up the stack
        // and repeatedly performing stackwalks (very inefficient).
        //
        // FIXME: there is something wrong with stackwalking across
        // adapter frames...this is likely to be the root cause of the
        // failure with the simpler algorithm below.

        for (long offset = 0; offset < regionInBytesToSearch; offset += vm.getAddressSize()) {
          try {
            Address curSP = sp.addOffsetTo(offset);
            Frame frame = new X86Frame(curSP, null, pc);
            RegisterMap map = thread.newRegisterMap(false);
            while (frame != null) {
              if (frame.isEntryFrame() && frame.entryFrameIsFirst()) {
                // We were able to traverse all the way to the
                // bottommost Java frame.
                // This sp looks good. Keep it.
                if (DEBUG) {
                  System.out.println("CurrentFrameGuess: Choosing sp = " + curSP + ", pc = " + pc);
                }
                setValues(curSP, null, pc);
                return true;
              }
              frame = frame.sender(map);
            }
          } catch (Exception e) {
            if (DEBUG) {
              System.out.println("CurrentFrameGuess: Exception " + e + " at offset " + offset);
            }
            // Bad SP. Try another.
          }
        }

        // Were not able to find a plausible SP to go with this PC.
        // Bail out.
        return false;

        /*
        // Original algorithm which does not work because SP was
        // pointing beyond where it should have:

        // For the server compiler, EBP is not guaranteed to be valid
        // for compiled code. We see whether the PC is in the
        // interpreter and take care of that, otherwise we run code
        // (unfortunately) duplicated from AMD64Frame.senderForCompiledFrame.

        CodeCache cc = vm.getCodeCache();
        if (cc.contains(pc)) {
          CodeBlob cb = cc.findBlob(pc);

          // See if we can derive a frame pointer from SP and PC
          // NOTE: This is the code duplicated from AMD64Frame
          Address saved_fp = null;
          int llink_offset = cb.getLinkOffset();
          if (llink_offset >= 0) {
            // Restore base-pointer, since next frame might be an interpreter frame.
            Address fp_addr = sp.addOffsetTo(VM.getVM().getAddressSize() * llink_offset);
            saved_fp = fp_addr.getAddressAt(0);
          }

          setValues(sp, saved_fp, pc);
          return true;
        }
        */
      }
    } else {
      // If the current program counter was not known to us as a Java
      // PC, we currently assume that we are in the run-time system
      // and attempt to look to thread-local storage for saved ESP and
      // EBP. Note that if these are null (because we were, in fact,
      // in Java code, i.e., vtable stubs or similar, and the SA
      // didn't have enough insight into the target VM to understand
      // that) then we are going to lose the entire stack trace for
      // the thread, which is sub-optimal. FIXME.

      if (DEBUG) {
        System.out.println(
            "CurrentFrameGuess: choosing last Java frame: sp = "
                + thread.getLastJavaSP()
                + ", fp = "
                + thread.getLastJavaFP());
      }
      if (thread.getLastJavaSP() == null) {
        return false; // No known Java frames on stack
      }
      setValues(thread.getLastJavaSP(), thread.getLastJavaFP(), null);
      return true;
    }
  }

  public Address getSP() {
    return spFound;
  }

  public Address getFP() {
    return fpFound;
  }
  /**
   * May be null if getting values from thread-local storage; take care to call the correct
   * AMD64Frame constructor to recover this if necessary
   */
  public Address getPC() {
    return pcFound;
  }

  private void setValues(Address sp, Address fp, Address pc) {
    spFound = sp;
    fpFound = fp;
    pcFound = pc;
  }
}
Exemplo n.º 2
0
 static {
   debug = System.getProperty("sun.jvm.hotspot.utilities.soql.SOQLEngine.debug") != null;
 }