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|
//! A simple runtime which can be used to execute emitted instructions.
use core::slice;
use nix::sys::mman::{mmap, mprotect, munmap, MapFlags, ProtFlags};
/// A simple `mmap`ed runtime with executable pages.
pub struct Runtime {
buf: *mut u8,
len: usize,
idx: usize,
}
impl Runtime {
/// Create a new [Runtime].
pub fn new() -> Runtime {
// Allocate a single page.
let len = core::num::NonZeroUsize::new(4096).unwrap();
let buf = unsafe {
mmap(
None,
len,
ProtFlags::PROT_WRITE | ProtFlags::PROT_READ | ProtFlags::PROT_EXEC,
MapFlags::MAP_PRIVATE | MapFlags::MAP_ANONYMOUS,
0, /* fd */
0, /* off */
)
.unwrap() as *mut u8
};
Runtime {
buf,
len: len.get(),
idx: 0,
}
}
/// Write protect the underlying code page(s).
pub fn protect(&mut self) {
unsafe {
// Remove write permissions from code buffer and allow to read-execute from it.
mprotect(
self.buf.cast(),
self.len,
ProtFlags::PROT_READ | ProtFlags::PROT_EXEC,
)
.expect("Failed to RX mprotect Runtime code buffer");
}
}
/// Add block of code to the runtime and get function pointer back.
pub unsafe fn add_code<F>(&mut self, code: impl AsRef<[u8]>) -> F {
// Get pointer to start of next free byte.
assert!(self.idx < self.len);
let fn_start = self.buf.add(self.idx);
// Copy over code.
let code = code.as_ref();
assert!(code.len() < (self.len - self.idx));
unsafe { std::ptr::copy_nonoverlapping(code.as_ptr(), fn_start, code.len()) };
// Increment index to next free byte.
self.idx += code.len();
// Return function to newly added code.
Self::as_fn::<F>(fn_start)
}
/// Reinterpret the block of code as `F`.
#[inline]
unsafe fn as_fn<F>(fn_start: *mut u8) -> F {
unsafe { std::mem::transmute_copy(&fn_start) }
}
/// Dump the currently added code to a file called `jit.asm`. The disassembly can be inspected
/// as `ndisasm -b 64 jit.asm`.
pub fn dump(&self) {
let code = unsafe { slice::from_raw_parts(self.buf, self.idx) };
std::fs::write("jit.asm", code).unwrap();
}
}
impl Drop for Runtime {
fn drop(&mut self) {
unsafe {
munmap(self.buf.cast(), self.len).expect("Failed to munmap Runtime");
}
}
}
|
