Backtrace from crashing target program

[Gabor Greif]

It appears that I ended up with the threaded runtime. While not
optimal for debugging, I see this:

Breakpoint 1, schedule (initialCapability=0x1032b680, task=0x10336ec8)
    at rts/Schedule.c:486
486             r = StgRun((StgFunPtr) stg_returnToStackTop, &cap->r);
(gdb) p cap->r
$6 = {rR1 = {w = 0, a = 0x0, c = 0, f = 0, i = 0, p = 0x0}, rR2 = {w =
0, a = 0x0,
    c = 0, f = 0, i = 0, p = 0x0}, rR3 = {w = 0, a = 0x0, c = 0, f = 0, i = 0,
    p = 0x0}, rR4 = {w = 0, a = 0x0, c = 0, f = 0, i = 0, p = 0x0},
rR5 = {w = 0,
    a = 0x0, c = 0, f = 0, i = 0, p = 0x0}, rR6 = {w = 0, a = 0x0, c =
0, f = 0,
    i = 0, p = 0x0}, rR7 = {w = 0, a = 0x0, c = 0, f = 0, i = 0, p =
0x0}, rR8 = {
    w = 0, a = 0x0, c = 0, f = 0, i = 0, p = 0x0}, rR9 = {w = 0, a =
0x0, c = 0,
    f = 0, i = 0, p = 0x0}, rR10 = {w = 0, a = 0x0, c = 0, f = 0, i =
0, p = 0x0},
  rF1 = 0, rF2 = 0, rF3 = 0, rF4 = 0, rD1 = 0, rD2 = 0, rL1 = 0, rSp = 0x0,
  rSpLim = 0x0, rHp = 0x0, rHpLim = 0x0, rCCCS = 0x0, rCurrentTSO = 0x301033c0,
  rNursery = 0x1032f178, rCurrentNursery = 0x30100040, rCurrentAlloc =
0x30100060,
  rHpAlloc = 0, rRet = 0}


After loading the thread state,

stg_returnToStackTop
{
  LOAD_THREAD_STATE();
  CHECK_SENSIBLE_REGS();
  jump %ENTRY_CODE(Sp(0));
}

rightly barfs that registers are zero. Which function sets up those?