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;
}
