Host Call Log (WAT)

A minimal WAT program that demonstrates PVM host calls. It invokes ecalli 100 (the log host call) to print “Hello from PVM!” and returns 42.

Source

File: examples/sources/host-call-log.wat

(module
  (import "env" "pvm_ptr" (func $pvm_ptr (param i64) (result i64)))
  (import "env" "host_call_5" (func $host_call_5 (param i64 i64 i64 i64 i64 i64) (result i64)))
  (memory (export "memory") 1)
  ;; "test-log" at offset 0 (8 bytes)
  (data (i32.const 0) "test-log")
  ;; "Hello from PVM!" at offset 8 (15 bytes)
  (data (i32.const 8) "Hello from PVM!")
  (func (export "main") (param $args_ptr i32) (param $args_len i32) (result i64)
    ;; ecalli 100 = log host call
    ;; r7 = level (3 = INFO)
    ;; r8 = target_ptr (PVM address of "test-log")
    ;; r9 = target_len (8)
    ;; r10 = msg_ptr (PVM address of "Hello from PVM!")
    ;; r11 = msg_len (15)
    (drop (call $host_call_5
      (i64.const 100)
      (i64.const 3)
      (call $pvm_ptr (i64.const 0))
      (i64.const 8)
      (call $pvm_ptr (i64.const 8))
      (i64.const 15)))
    ;; Return result: store 42 at offset 24, return (ptr=24, len=4)
    (i32.store (i32.const 24) (i32.const 42))
    (i64.const 17179869208)))

The program uses two imported helpers:

• pvm_ptr – translates a Wasm linear-memory offset to a PVM address
• host_call_5 – dispatches to a numbered host function with 5 data arguments (here, ecalli 100 for logging). The _5 suffix indicates the number of data registers (r7-r11) passed to the host call.

Compiled Metadata

Decompiled Output

./target/release/pvm-decompiler examples/compiled/host-call-log.pvm

fn main(r0: u64, r1: u64, r3: u64, r5: u64, r6: u64, r7: u64, r12: u64) {
    let var_28
    // @0006
    log()
    u32[var_28 + 0x33000] = 42
    halt()
}

What to notice:

• Host call recognition: The ecalli 100 instruction is recognized and rendered as log(). The decompiler collapses the multi-register setup (level, target pointer/length, message pointer/length) into a single named call.
• Compact output: Despite the binary being ~12 KB (due to the pvm_ptr helper and runtime support code being compiled in), the decompiler produces just 7 lines of pseudo-code for the main function.
• Result encoding: u32[var_28 + 0x33000] = 42 stores the return value, followed by halt().
• Binary size vs. complexity: The 12 KB binary size comes from the pvm_ptr address-translation helper and memory setup code compiled from the imports, not from the application logic itself.