debug.getstack

Reads values from the Luau VMLuau VMThe Luau Virtual Machine — a register-based bytecode interpreter. Executes compiled Luau instructions sequentially, managing a value stack, call stack, and upvalue chains. Roblox runs one VM per Actor context. stack at the specified call level. If index is given, returns the single stack slot at that position. If omitted, returns the entire stack frameCall stackThe chain of CallInfo frames representing nested function calls. Each frame records the closure, base register, top, and saved program counter. Walking the call stack reveals the full execution trace. as an array. Stack level 1 is the calling function, 2 is its caller, etc.

The Luau VMLuau VMThe Luau Virtual Machine — a register-based bytecode interpreter. Executes compiled Luau instructions sequentially, managing a value stack, call stack, and upvalue chains. Roblox runs one VM per Actor context. maintains a call stackCall stackThe chain of CallInfo frames representing nested function calls. Each frame records the closure, base register, top, and saved program counter. Walking the call stack reveals the full execution trace. as an array of CallInfo structures:

typedef struct CallInfo {
  StkId base;     // base register pointer into L->stack
  StkId func;     // pointer to the function TValue
  StkId top;      // top of available stack for this frame
  const Instruction* savedpc;
} CallInfo;

Stack slots within a frame are registers. R(0) is at ci->base + 0, R(1) at ci->base + 1, etc. The compiler assigns locals to specific registers:

• Parameters: R(0) through R(numparams-1)
• Local variables: subsequent registers in declaration order
• Temporaries: subexpressions and intermediate values

debug.getstack(level, index) reads ci->base[index - 1] (1-based to 0-based conversion).