(module ;; Import the required fd_write WASI function which will write the given io vectors to stdout ;; The function signature for fd_write is: ;; (File Descriptor, *iovs, iovs_len, nwritten) -> Returns number of bytes written (import "wasi_unstable" "fd_write" (func $fd_write (param i32 i32 i32 i32) (result i32))) (memory 1) (export "memory" (memory 0)) ;; Write 'hello world\n' to memory at an offset of 8 bytes ;; Note the trailing newline which is required for the text to appear (data (i32.const 8) "hello world\n") (func $main (export "_start") ;; Creating a new io vector within linear memory (i32.store (i32.const 0) (i32.const 8)) ;; iov.iov_base - This is a pointer to the start of the 'hello world\n' string (i32.store (i32.const 4) (i32.const 12)) ;; iov.iov_len - The length of the 'hello world\n' string (call $fd_write (i32.const 1) ;; file_descriptor - 1 for stdout (i32.const 0) ;; *iovs - The pointer to the iov array, which is stored at memory location 0 (i32.const 1) ;; iovs_len - We're printing 1 string stored in an iov - so one. (i32.const 20) ;; nwritten - A place in memory to store the number of bytes written ) drop ;; Discard the number of bytes written from the top of the stack ))