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
emitServiceReqWork(CodeBlock& cb, TCA start, bool persist, SRFlags flags,
ServiceRequest req, const ServiceReqArgVec& argv) {
assert(start);
const bool align = flags & SRFlags::Align;
Asm as { cb };
/*
* Remember previous state of the code cache.
*/
boost::optional<CodeCursor> maybeCc = boost::none;
if (start != as.frontier()) {
maybeCc = boost::in_place<CodeCursor>(boost::ref(as), start);
}
/* max space for moving to align, saving VM regs plus emitting args */
static const int
kVMRegSpace = 0x14,
kMovSize = 0xa,
kNumServiceRegs = sizeof(serviceReqArgRegs) / sizeof(PhysReg),
kMaxStubSpace = kJmpTargetAlign - 1 + kVMRegSpace +
kNumServiceRegs * kMovSize;
if (align) {
moveToAlign(cb);
}
TCA retval = as.frontier();
TRACE(3, "Emit Service Req @%p %s(", start, serviceReqName(req));
/*
* Move args into appropriate regs. Eager VMReg save may bash flags,
* so set the CondCode arguments first.
*/
for (int i = 0; i < argv.size(); ++i) {
assert(i < kNumServiceReqArgRegs);
auto reg = serviceReqArgRegs[i];
const auto& argInfo = argv[i];
switch(argv[i].m_kind) {
case ServiceReqArgInfo::Immediate: {
TRACE(3, "%" PRIx64 ", ", argInfo.m_imm);
as. emitImmReg(argInfo.m_imm, reg);
} break;
case ServiceReqArgInfo::CondCode: {
// Already set before VM reg save.
DEBUG_ONLY TCA start = as.frontier();
as. setcc(argInfo.m_cc, rbyte(reg));
assert(start - as.frontier() <= kMovSize);
TRACE(3, "cc(%x), ", argInfo.m_cc);
} break;
default: not_reached();
}
}
emitEagerVMRegSave(as, RegSaveFlags::SaveFP);
if (persist) {
as. emitImmReg(0, Transl::reg::rAsm);
} else {
as. emitImmReg((uint64_t)start, Transl::reg::rAsm);
}
TRACE(3, ")\n");
as. emitImmReg(req, Transl::reg::rdi);
/*
* Weird hand-shaking with enterTC: reverse-call a service routine.
*
* In the case of some special stubs (m_callToExit, m_retHelper), we
* have already unbalanced the return stack by doing a ret to
* something other than enterTCHelper. In that case
* SRJmpInsteadOfRet indicates to fake the return.
*/
if (flags & SRFlags::JmpInsteadOfRet) {
as. pop(Transl::reg::rax);
as. jmp(Transl::reg::rax);
} else {
as. ret();
}
// TODO(2796856): we should record an OpServiceRequest pseudo-bytecode here.
translator_not_reached(as);
if (!persist) {
/*
* Recycled stubs need to be uniformly sized. Make space for the
* maximal possible service requests.
*/
assert(as.frontier() - start <= kMaxStubSpace);
as.emitNop(start + kMaxStubSpace - as.frontier());
assert(as.frontier() - start == kMaxStubSpace);
}
return retval;
}