Traps

A trap is a runtime error that aborts execution. Common sources:

• unreachable executed
• Integer division by zero
• Signed overflow: i32.div_s with INT_MIN / -1
• call_indirect type mismatch or out-of-bounds table index
• Out-of-bounds memory access

unreachable

(module
  (func (param $x i32)
    (if (i32.lt_s (local.get $x) (i32.const 0))
      (then (unreachable))))
)

Memory out-of-bounds

(module
  (memory 1)
  (func
    (drop (i32.load (i32.const 70000))))  ;; > 64 KiB — traps
)

call_indirect mismatch

(module
  (type $t0 (func (param i32) (result i32)))
  (func $f0 (type $t0) (param $x i32) (result i32)
    (local.get $x))
  (table 1 funcref)
  (elem (i32.const 0) $f0)
  (func (param $x i32) (result i32)
    (call_indirect (type $t0) (local.get $x) (i32.const 0)))
)

Instruction Reference

• Control Flow Instructions — unreachable, call_indirect
• i32 Instructions — i32.div_s, i32.load, i32.store