I'm using rust dylib to make hash algorithm plugable.
I referred this article: https://michael-f-bryan.github.io/rust-ffi-guide/dynamic_loading.html#running-the-plugin
Suppose there are 2 crate:
app: load a dylib
hash_algo: provide a dylib
Define a trait (in crate app)
pub trait Hash {
fn hash(&self, out: &mut [u8], data: &[u8]);
}
Impl the trait (in crate hash_algo)
pub struct Blake2b256;
impl Hash for Blake2b256 {
fn hash(&self, out: &mut [u8], data: &[u8]) {
assert_eq!(out.len(), self.key_length().into());
blake2b::Blake2b::blake2b(out, data, &[]);
}
}
Provide a FFI function (in crate hash_algo)
#[no_mangle]
pub extern "C" fn _crypto_hash_create() -> *mut dyn Hash {
let boxed: Box<dyn Hash> = Box::new(Blake2b256);
Box::into_raw(boxed)
}
Load and use the dylib (in crate app)
fn main() -> errors::Result<()> {
let path = PathBuf::from(&other);
let hasher = load_custom_lib(&path)?;
// the following code does not work
let data = [0u8, 1u8, 2u8];
let mut out = [0u8; 32];
hasher.hash(&mut out, &data);
}
fn load_custom_lib(path: &PathBuf) -> errors::Result<Box<dyn Hash>> {
if !path.exists() {
bail!(errors::ErrorKind::CustomLibNotFound(format!("{:?}", path)));
}
let lib = Library::new(path)
.map_err(|_| errors::ErrorKind::CustomLibLoadFailed(format!("{:?}", path)))?;
type Constructor = unsafe extern "C" fn() -> *mut dyn Hash;
let hasher: Box<dyn Hash> = unsafe {
let constructor: Symbol<Constructor> = lib
.get(b"_crypto_hash_create")
.map_err(|_| errors::ErrorKind::CustomLibLoadFailed(format!("{:?}", path)))?;
let boxed_raw = constructor();
let hash = Box::from_raw(boxed_raw);
hash
};
// the following code works
let data = [0u8, 1u8, 2u8];
let mut out = [0u8; 32];
hasher.hash(&mut out, &data);
Ok(hasher)
}
What's weird is:
On macos
rustc 1.39.0 (4560ea788 2019-11-04)
Both the codes in fn load_custom_lib and fn main work.
On windows
rustc 1.41.1 (f3e1a954d 2020-02-24)
The code in fn load_custom_lib works,
while the code in fn main get a runtime error:
(exit code: 0xc0000005, STATUS_ACCESS_VIOLATION)
Segmentation fault
On linux
rustc 1.42.0 (b8cedc004 2020-03-09)
The code in fn load_custom_lib works,
while the code in fn main get a runtime error:
(signal: 11, SIGSEGV: invalid memory reference)
I wonder why after a function return,
the Box will not work.