---
tags: wasm
title: WASM linking
---

# Archlinux

pacman -Syu wasi-libc wasi-compiler-rt wabt

# Installer in Rust

- `src/lib.rs`

#![no_std]

#[panic_handler]
fn panic(_:&::core::panic::PanicInfo) -> ! {
    loop{}
}

#[link(name = "module_hash", kind = "static")]
extern {
    static MODULE_HASH: *const u8;
}

#[no_mangle]
pub unsafe extern "C" fn get_hash() -> *const u8 {
    MODULE_HASH
}

- Compile with

rustc -C opt-level=2 --target=wasm32-unknown-unknown --crate-type=staticlib --print native-static-libs --emit=obj -C panic=abort src/lib.rs -o installer.o

# Module hash object

- `module_hash.c`

char const * MODULE_HASH = "deadbeef";

- Compile with

clang -o module_hash.o --target=wasm32 -nostdlib -Wl,-r -Wl,--no-entry -Wl,--export-all module_hash.c

# Link all

wasm-ld --no-entry --export-all installer.o module_hash.o -o installer.wasm

The result is the following WAT.

(module
  (type (;0;) (func))
  (type (;1;) (func (param i32)))
  (type (;2;) (func (result i32)))
  (func $__wasm_call_ctors (type 0))
  (func $rust_begin_unwind (type 1) (param i32)
    loop  ;; label = @1
      br 0 (;@1;)
    end)
  (func $get_hash (type 2) (result i32)
    i32.const 0
    i32.load offset=1036)
  (memory (;0;) 2)
  (global $__stack_pointer (mut i32) (i32.const 66576))
  (global (;1;) i32 (i32.const 1036))
  (global (;2;) i32 (i32.const 1024))
  (global (;3;) i32 (i32.const 1040))
  (global (;4;) i32 (i32.const 1024))
  (global (;5;) i32 (i32.const 66576))
  (global (;6;) i32 (i32.const 0))
  (global (;7;) i32 (i32.const 1))
  (export "memory" (memory 0))
  (export "__wasm_call_ctors" (func $__wasm_call_ctors))
  (export "rust_begin_unwind" (func $rust_begin_unwind))
  (export "get_hash" (func $get_hash))
  (export "MODULE_HASH" (global 1)) (; location of the module hash ;)
  (export "__dso_handle" (global 2))
  (export "__data_end" (global 3))
  (export "__global_base" (global 4))
  (export "__heap_base" (global 5))
  (export "__memory_base" (global 6))
  (export "__table_base" (global 7))
  (data $.rodata (i32.const 1024) "deadbeef\00")
  (data $.data (i32.const 1036) "\00\04\00\00"))

It looks legit so far. :smiley: