Re: Porting to Darwin

I'm only able to work on this in spurts, which makes for rather slow
going.  Hyungyip Kim is right: according to the apple docs and other
webpages I've found, the 16-byte stack alignment is necessary for SSE.

What I've done right now is hack MacroAssembler::call_C to align the
stack before the call like the following:

 void MacroAssembler::call_C(Register entry) {
   set_last_Delta_frame_before_call();
-  call(entry);
+#ifdef ALIGN_STACK
+  // align stack to N-byte boundary; assumes esp grows down
+  // which is true on intel.  Assumes ebx is preserved across
+  // the call
+  pushl(ebx);
+  movl(ebx,esp);	// remember unaligned esp
+  subl(esp,4);		// add space for unaligned esp
+  andl(esp, -ALIGN_STACK); // with the subl, we have at least 4 bytes
avail
+  addl(esp,4);
+  pushl(ebx);
+  call(entry);
+  popl(ebx);
+  movl(esp,ebx);	// restore stack pointer prior to alignment
+  popl(ebx);
+#else
+  call(entry);
+#endif
   reset_last_Delta_frame();
 }

This allows execution to progress a bit further, but the VM crashes as
the program counter (PC) obtained from the last_frame (that is
frame::_pc) of the delta process is out of range.  This frame is being
spoofed up from the following constructor (vm/runtime/frame.hpp lines
72--76):

  frame(oop* sp, int* fp) {
    _sp = sp;
    _fp = fp;
    _pc = (char*) sp[-1];
  }

That last line is returning a pointer with address 0x89, which I
suspect indicates that the stack layout assumed of the delta processes
is different from the reality.

(gdb) down
#0  frame::frame (this=0xb0102da4, sp=0xb0102e60, fp=0xb0102e6c) at
frame.hpp:76
76	    _pc = (char*) sp[-1];
(gdb) p sp[-1]
$7 = (oopDesc *) 0x89
(gdb) p sp[0]
$8 = (oopDesc *) 0x10a1b29

Those sp and fp values don't match the values I see for the frames in
gdb though.

I need to figure out more about the delta processes and what they're
recording on the stack.

Brian.
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