/**
* 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;
}
}
static {
debug = System.getProperty("sun.jvm.hotspot.utilities.soql.SOQLEngine.debug") != null;
}