Need some help: 8133646: x86/vm/macroAssembler_x86.cpp:886 DEBUG MESSAGE: StubRoutines::call_stub: threads must correspond

[David Holmes]

Hi Compiler and x86_64 code experts, :)

Bug: https://bugs.openjdk.java.net/browse/JDK-8133646

There's a chance this failure is related to my recent changes under 
8130212:

http://hg.openjdk.java.net/jdk9/hs-rt/hotspot/rev/d5b328043c10

Given the failing debug code:

    367 #ifdef ASSERT
    368 // verify that threads correspond
    369 {
    370 Label L, S;
    371 __ cmpptr(r15_thread, thread);
    372 __ jcc(Assembler::notEqual, S);
    373 __ get_thread(rbx);
    374 __ cmpptr(r15_thread, rbx);
    375 __ jcc(Assembler::equal, L);
    376 __ bind(S);
    377 __ jcc(Assembler::equal, L);
    378 __ stop("StubRoutines::call_stub: threads must correspond");
    379 __ bind(L);
    380 }
    381 #endif

and given the definition of get_thread:

// This is simply a call to ThreadLocalStorage::thread()
void MacroAssembler::get_thread(Register thread) {
   if (thread != rax) {
     push(rax);
   }
   push(rdi);
   push(rsi);
   push(rdx);
   push(rcx);
   push(r8);
   push(r9);
   push(r10);
   push(r11);

   call(RuntimeAddress(CAST_FROM_FN_PTR(address, 
ThreadLocalStorage::thread)));

   pop(r11);
   pop(r10);
   pop(r9);
   pop(r8);
   pop(rcx);
   pop(rdx);
   pop(rsi);
   pop(rdi);

   if (thread != rax) {
     movl(thread, rax);
     pop(rax);
   }
}

where ThreadLocalStorage::thread() is simply:

inline Thread* ThreadLocalStorage::thread()  {
   return _thr_current;
}

and _thr_current is a compiler-defined thread-local variable:

static __thread Thread * _thr_current;

Can anyone see anything that might cause an issue? I was wondering 
whether I have to verify that r15 is preserved by the actual 
thread-local access? IIUC normally the get_thread slow-path would be 
used to set r15_thread and so we wouldn't notice if it got trashed under 
some circumstances. It obviously doesn't always get trashed because the 
bug has only been seen to occur once. And of course the failure could be 
completely incidental to my changes. :)

Thanks,
David