TCA emitCallToExit(CodeBlock& cb) {
Asm a { cb };
// Emit a byte of padding. This is a kind of hacky way to avoid
// hitting an assert in recordGdbStub when we call it with stub - 1
// as the start address.
a.emitNop(1);
auto const start = a.frontier();
if (RuntimeOption::EvalHHIRGenerateAsserts) {
Label ok;
a.emitImmReg(uintptr_t(enterTCExit), rax);
a.cmpq(rax, *rsp());
a.je8 (ok);
a.ud2();
asm_label(a, ok);
}
// Emulate a ret to enterTCExit without actually doing one to avoid
// unbalancing the return stack buffer. The call from enterTCHelper() that
// got us into the TC was popped off the RSB by the ret that got us to this
// stub.
a.addq(8, rsp());
a.jmp(TCA(enterTCExit));
// On a backtrace, gdb tries to locate the calling frame at address
// returnRIP-1. However, for the first VM frame, there is no code at
// returnRIP-1, since the AR was set up manually. For this frame,
// record the tracelet address as starting from this callToExit-1,
// so gdb does not barf.
return start;
}
TCA emitFreeLocalsHelpers(CodeBlock& cb, UniqueStubs& us) {
Label doRelease;
Label release;
Label loopHead;
auto const rData = rarg(0); // not live coming in, but used
// for destructor calls
auto const rIter = rarg(1); // live coming in
auto const rFinished = rdx;
auto const rType = ecx;
int const tvSize = sizeof(TypedValue);
Asm a { cb };
align(cb, Alignment::CacheLine, AlignContext::Dead);
auto const start = a.frontier();
asm_label(a, release);
a. loadq (rIter[TVOFF(m_data)], rData);
a. cmpl (1, rData[FAST_REFCOUNT_OFFSET]);
jccBlock<CC_L>(a, [&] {
a. jz8 (doRelease);
a. decl (rData[FAST_REFCOUNT_OFFSET]);
});
a. ret ();
asm_label(a, doRelease);
a. push (rIter);
a. push (rFinished);
a. call (lookupDestructor(a, PhysReg(rType)));
// Three quads between where %rsp is now and the saved RIP of the call into
// the stub: two from the pushes above, and one for the saved RIP of the call
// to `release' done below (e.g., in emitDecLocal).
mcg->fixupMap().recordFixup(a.frontier(), makeIndirectFixup(3));
a. pop (rFinished);
a. pop (rIter);
a. ret ();
auto emitDecLocal = [&]() {
Label skipDecRef;
// Zero-extend the type while loading so it can be used as an array index
// to lookupDestructor() above.
emitLoadTVType(a, rIter[TVOFF(m_type)], rType);
emitCmpTVType(a, KindOfRefCountThreshold, rbyte(rType));
a. jle8 (skipDecRef);
a. call (release);
asm_label(a, skipDecRef);
};
alignJmpTarget(cb);
us.freeManyLocalsHelper = a.frontier();
a. lea (rvmfp()[-(jit::kNumFreeLocalsHelpers * sizeof(Cell))],
rFinished);
// Loop for the first few locals, but unroll the final kNumFreeLocalsHelpers.
asm_label(a, loopHead);
emitDecLocal();
a. addq (tvSize, rIter);
a. cmpq (rIter, rFinished);
a. jnz8 (loopHead);
for (int i = 0; i < kNumFreeLocalsHelpers; ++i) {
us.freeLocalsHelpers[kNumFreeLocalsHelpers - i - 1] = a.frontier();
emitDecLocal();
if (i != kNumFreeLocalsHelpers - 1) {
a.addq (tvSize, rIter);
}
}
a. ret ();
// Keep me small!
always_assert(Stats::enabled() ||
(a.frontier() - start <= 4 * kX64CacheLineSize));
return start;
}