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</pre></div><pre class="rust"><code><span class="doccomment">//! A simple runtime which can be used to execute emitted instructions.
</span><span class="kw">use </span>core::slice;
<span class="kw">use </span>nix::sys::mman::{mmap, mprotect, munmap, MapFlags, ProtFlags};
<span class="doccomment">/// A simple `mmap`ed runtime with executable pages.
</span><span class="kw">pub struct </span>Runtime {
buf: <span class="kw-2">*mut </span>u8,
len: usize,
idx: usize,
}
<span class="kw">impl </span>Runtime {
<span class="doccomment">/// Create a new [Runtime].
</span><span class="kw">pub fn </span>new() -> Runtime {
<span class="comment">// Allocate a single page.
</span><span class="kw">let </span>len = core::num::NonZeroUsize::new(<span class="number">4096</span>).unwrap();
<span class="kw">let </span>buf = <span class="kw">unsafe </span>{
mmap(
<span class="prelude-val">None</span>,
len,
ProtFlags::PROT_WRITE | ProtFlags::PROT_READ | ProtFlags::PROT_EXEC,
MapFlags::MAP_PRIVATE | MapFlags::MAP_ANONYMOUS,
<span class="number">0</span>, <span class="comment">/* fd */
</span><span class="number">0</span>, <span class="comment">/* off */
</span>)
.unwrap() <span class="kw">as </span><span class="kw-2">*mut </span>u8
};
Runtime {
buf,
len: len.get(),
idx: <span class="number">0</span>,
}
}
<span class="doccomment">/// Write protect the underlying code page(s).
</span><span class="kw">pub fn </span>protect(<span class="kw-2">&mut </span><span class="self">self</span>) {
<span class="kw">unsafe </span>{
<span class="comment">// Remove write permissions from code buffer and allow to read-execute from it.
</span>mprotect(
<span class="self">self</span>.buf.cast(),
<span class="self">self</span>.len,
ProtFlags::PROT_READ | ProtFlags::PROT_EXEC,
)
.expect(<span class="string">"Failed to RX mprotect Runtime code buffer"</span>);
}
}
<span class="doccomment">/// Add block of code to the runtime and get function pointer back.
</span><span class="kw">pub unsafe fn </span>add_code<F>(<span class="kw-2">&mut </span><span class="self">self</span>, code: <span class="kw">impl </span>AsRef<[u8]>) -> F {
<span class="comment">// Get pointer to start of next free byte.
</span><span class="macro">assert!</span>(<span class="self">self</span>.idx < <span class="self">self</span>.len);
<span class="kw">let </span>fn_start = <span class="self">self</span>.buf.add(<span class="self">self</span>.idx);
<span class="comment">// Copy over code.
</span><span class="kw">let </span>code = code.as_ref();
<span class="macro">assert!</span>(code.len() < (<span class="self">self</span>.len - <span class="self">self</span>.idx));
<span class="kw">unsafe </span>{ std::ptr::copy_nonoverlapping(code.as_ptr(), fn_start, code.len()) };
<span class="comment">// Increment index to next free byte.
</span><span class="self">self</span>.idx += code.len();
<span class="comment">// Return function to newly added code.
</span><span class="self">Self</span>::as_fn::<F>(fn_start)
}
<span class="doccomment">/// Reinterpret the block of code as `F`.
</span><span class="attr">#[inline]
</span><span class="kw">unsafe fn </span>as_fn<F>(fn_start: <span class="kw-2">*mut </span>u8) -> F {
<span class="kw">unsafe </span>{ std::mem::transmute_copy(<span class="kw-2">&</span>fn_start) }
}
<span class="doccomment">/// Dump the currently added code to a file called `jit.asm`. The disassembly can be inspected
/// as `ndisasm -b 64 jit.asm`.
</span><span class="kw">pub fn </span>dump(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="kw">let </span>code = <span class="kw">unsafe </span>{ slice::from_raw_parts(<span class="self">self</span>.buf, <span class="self">self</span>.idx) };
std::fs::write(<span class="string">"jit.asm"</span>, code).unwrap();
}
}
<span class="kw">impl </span>Drop <span class="kw">for </span>Runtime {
<span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) {
<span class="kw">unsafe </span>{
munmap(<span class="self">self</span>.buf.cast(), <span class="self">self</span>.len).expect(<span class="string">"Failed to munmap Runtime"</span>);
}
}
}
</code></pre></div></section></main></body></html>
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