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; }