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id="257">257</a> <a href="#258" id="258">258</a> <a href="#259" id="259">259</a> <a href="#260" id="260">260</a> </pre></div><pre class="rust"><code><span class="doccomment">//! Simple `mmap`ed runtime. //! //! This runtime supports adding code to executable pages and turn the added code into user //! specified function pointer. </span><span class="attr">#[cfg(not(target_os = <span class="string">"linux"</span>))] </span><span class="macro">compile_error!</span>(<span class="string">"This runtime is only supported on linux"</span>); <span class="kw">use </span>nix::sys::mman::{mmap, mprotect, munmap, MapFlags, ProtFlags}; <span class="kw">mod </span>perf { <span class="kw">use </span>std::fs; <span class="kw">use </span>std::io::Write; <span class="doccomment">/// Provide support for the simple [perf jit interface][perf-jit]. /// /// This allows a simple (static) jit runtime to generate meta data describing the generated /// functions, which is used during post-processing by `perf report` to symbolize addresses /// captured while executing jitted code. /// /// By the nature of this format, this can not be used for dynamic jit runtimes, which reuses /// memory which previously contained jitted code. /// /// [perf-jit]: https://elixir.bootlin.com/linux/v6.6.6/source/tools/perf/Documentation/jit-interface.txt </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">struct </span>PerfMap { file: std::fs::File, } <span class="kw">impl </span>PerfMap { <span class="doccomment">/// Create an empty perf map file. </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>new() -> <span class="self">Self </span>{ <span class="kw">let </span>name = <span class="macro">format!</span>(<span class="string">"/tmp/perf-{}.map"</span>, nix::unistd::getpid()); <span class="kw">let </span>file = fs::OpenOptions::new() .truncate(<span class="bool-val">true</span>) .create(<span class="bool-val">true</span>) .write(<span class="bool-val">true</span>) .open(<span class="kw-2">&</span>name) .unwrap_or_else(|<span class="kw">_</span>| <span class="macro">panic!</span>(<span class="string">"Failed to open perf map file {}"</span>, <span class="kw-2">&</span>name)); PerfMap { file } } <span class="doccomment">/// Add an entry to the perf map file. </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>add_entry(<span class="kw-2">&mut </span><span class="self">self</span>, start: usize, len: usize) { <span class="comment">// Each line has the following format, fields separated with spaces: // START SIZE NAME // // START and SIZE are hex numbers without 0x. // NAME is the rest of the line, so it could contain special characters. </span><span class="macro">writeln!</span>(<span class="self">self</span>.file, <span class="string">"{:x} {:x} jitfn_{:x}"</span>, start, len, start) .expect(<span class="string">"Failed to write PerfMap entry"</span>); } } } <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, perf: <span class="prelude-ty">Option</span><perf::PerfMap>, } <span class="kw">impl </span>Runtime { <span class="doccomment">/// Create a new [Runtime]. /// /// # Panics /// /// Panics if the `mmap` call fails. </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>).expect(<span class="string">"Value is non zero"</span>); <span class="kw">let </span>buf = <span class="kw">unsafe </span>{ mmap( <span class="prelude-val">None</span>, len, ProtFlags::PROT_NONE, 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>) .expect(<span class="string">"Failed to mmap runtime code page"</span>) <span class="kw">as </span><span class="kw-2">*mut </span>u8 }; Runtime { buf, len: len.get(), idx: <span class="number">0</span>, perf: <span class="prelude-val">None</span>, } } <span class="kw">pub fn </span>with_profile() -> Runtime { <span class="kw">let </span><span class="kw-2">mut </span>rt = Runtime::new(); rt.perf = <span class="prelude-val">Some</span>(perf::PerfMap::new()); rt } <span class="doccomment">/// Add the block of `code` to the runtime and a get function pointer of type `F`. /// /// # Panics /// /// Panics if the `code` does not fit on the `mmap`ed pages or is empty. /// /// # Safety /// /// The code added must fulfill the ABI of the specified function `F` and the returned function /// pointer is only valid until the [`Runtime`] is dropped. /// /// # Examples /// /// ``` /// let mut rt = juicebox_asm::Runtime::new(); /// /// let code = [ 0x90 /* nop */, 0xc3 /* ret */ ]; /// let nop = unsafe { rt.add_code::<extern "C" fn()>(&code) }; /// /// nop(); /// ``` </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="string">"Runtime code page full"</span>); <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.is_empty(), <span class="string">"Adding empty code not supported"</span>); <span class="macro">assert!</span>( code.len() <= (<span class="self">self</span>.len - <span class="self">self</span>.idx), <span class="string">"Code does not fit on the runtime code page" </span>); <span class="self">self</span>.unprotect(); <span class="kw">unsafe </span>{ std::ptr::copy_nonoverlapping(code.as_ptr(), fn_start, code.len()) }; <span class="self">self</span>.protect(); <span class="comment">// Increment index to next free byte. </span><span class="self">self</span>.idx += code.len(); <span class="comment">// Add perf map entry. </span><span class="kw">if let </span><span class="prelude-val">Some</span>(map) = <span class="kw-2">&mut </span><span class="self">self</span>.perf { map.add_entry(fn_start <span class="kw">as </span>usize, code.len()); } <span class="comment">// Return function to newly added code. </span><span class="kw">unsafe </span>{ <span class="self">Self</span>::as_fn::<F>(fn_start) } } <span class="doccomment">/// Dump the code added so far to the runtime into a file called `jit.asm` in the processes /// current working directory. /// /// The code can be inspected with a disassembler as for example `ndiasm` from /// [nasm.us](https://nasm.us/index.php). /// ```sh /// ndisasm -b 64 jit.asm /// ``` /// /// # Panics /// /// Panics if writing the file failed. </span><span class="kw">pub fn </span>dump(<span class="kw-2">&</span><span class="self">self</span>) { <span class="macro">assert!</span>(<span class="self">self</span>.idx <= <span class="self">self</span>.len); <span class="kw">let </span>code = <span class="kw">unsafe </span>{ core::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).expect(<span class="string">"Failed to write file"</span>); } <span class="doccomment">/// Reinterpret the block of code pointed to by `fn_start` 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">/// Add write protection the underlying code page(s). /// /// # Panics /// /// Panics if the `mprotect` call fails. </span><span class="kw">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 page 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 page"</span>); } } <span class="doccomment">/// Remove write protection the underlying code page(s). /// /// # Panics /// /// Panics if the `mprotect` call fails. </span><span class="kw">fn </span>unprotect(<span class="kw-2">&mut </span><span class="self">self</span>) { <span class="kw">unsafe </span>{ <span class="comment">// Add write permissions to code page. </span>mprotect(<span class="self">self</span>.buf.cast(), <span class="self">self</span>.len, ProtFlags::PROT_WRITE) .expect(<span class="string">"Failed to W mprotect runtime code page"</span>); } } } <span class="kw">impl </span>Drop <span class="kw">for </span>Runtime { <span class="doccomment">/// Unmaps the code page. This invalidates all the function pointer returned by /// [`Runtime::add_code`]. </span><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>); } } } <span class="attr">#[cfg(test)] </span><span class="kw">mod </span>test { <span class="kw">use super</span>::<span class="kw-2">*</span>; <span class="attr">#[test] </span><span class="kw">fn </span>test_code_max_size() { <span class="kw">let </span><span class="kw-2">mut </span>rt = Runtime::new(); <span class="kw">let </span>code = [<span class="number">0u8</span>; <span class="number">4096</span>]; <span class="kw">unsafe </span>{ rt.add_code::<<span class="kw">extern </span><span class="string">"C" </span><span class="kw">fn</span>()>(code); } } <span class="attr">#[test] #[should_panic] </span><span class="kw">fn </span>test_code_max_size_plus_1() { <span class="kw">let </span><span class="kw-2">mut </span>rt = Runtime::new(); <span class="kw">let </span>code = [<span class="number">0u8</span>; <span class="number">4097</span>]; <span class="kw">unsafe </span>{ rt.add_code::<<span class="kw">extern </span><span class="string">"C" </span><span class="kw">fn</span>()>(code); } } <span class="attr">#[test] #[should_panic] </span><span class="kw">fn </span>test_code_max_size_plus_1_2() { <span class="kw">let </span><span class="kw-2">mut </span>rt = Runtime::new(); <span class="kw">let </span>code = [<span class="number">0u8</span>; <span class="number">4096</span>]; <span class="kw">unsafe </span>{ rt.add_code::<<span class="kw">extern </span><span class="string">"C" </span><span class="kw">fn</span>()>(code); } <span class="kw">let </span>code = [<span class="number">0u8</span>; <span class="number">1</span>]; <span class="kw">unsafe </span>{ rt.add_code::<<span class="kw">extern </span><span class="string">"C" </span><span class="kw">fn</span>()>(code); } } <span class="attr">#[test] #[should_panic] </span><span class="kw">fn </span>test_empty_code() { <span class="kw">let </span><span class="kw-2">mut </span>rt = Runtime::new(); <span class="kw">let </span>code = [<span class="number">0u8</span>; <span class="number">0</span>]; <span class="kw">unsafe </span>{ rt.add_code::<<span class="kw">extern </span><span class="string">"C" </span><span class="kw">fn</span>()>(code); } } } </code></pre></div></section></main></body></html>