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</pre><div class="example-wrap"><pre class="rust ">
<span class="doccomment">/// Backtrace support built on libgcc with some extra OS-specific support</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Some methods of getting a backtrace:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * The backtrace() functions on unix. It turns out this doesn't work very</span>
<span class="doccomment">/// well for green threads on macOS, and the address to symbol portion of it</span>
<span class="doccomment">/// suffers problems that are described below.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * Using libunwind. This is more difficult than it sounds because libunwind</span>
<span class="doccomment">/// isn't installed everywhere by default. It's also a bit of a hefty library,</span>
<span class="doccomment">/// so possibly not the best option. When testing, libunwind was excellent at</span>
<span class="doccomment">/// getting both accurate backtraces and accurate symbols across platforms.</span>
<span class="doccomment">/// This route was not chosen in favor of the next option, however.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * We're already using libgcc_s for exceptions in rust (triggering thread</span>
<span class="doccomment">/// unwinding and running destructors on the stack), and it turns out that it</span>
<span class="doccomment">/// conveniently comes with a function that also gives us a backtrace. All of</span>
<span class="doccomment">/// these functions look like _Unwind_*, but it's not quite the full</span>
<span class="doccomment">/// repertoire of the libunwind API. Due to it already being in use, this was</span>
<span class="doccomment">/// the chosen route of getting a backtrace.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// After choosing libgcc_s for backtraces, the sad part is that it will only</span>
<span class="doccomment">/// give us a stack trace of instruction pointers. Thankfully these instruction</span>
<span class="doccomment">/// pointers are accurate (they work for green and native threads), but it's</span>
<span class="doccomment">/// then up to us again to figure out how to translate these addresses to</span>
<span class="doccomment">/// symbols. As with before, we have a few options. Before, that, a little bit</span>
<span class="doccomment">/// of an interlude about symbols. This is my very limited knowledge about</span>
<span class="doccomment">/// symbol tables, and this information is likely slightly wrong, but the</span>
<span class="doccomment">/// general idea should be correct.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// When talking about symbols, it's helpful to know a few things about where</span>
<span class="doccomment">/// symbols are located. Some symbols are located in the dynamic symbol table</span>
<span class="doccomment">/// of the executable which in theory means that they're available for dynamic</span>
<span class="doccomment">/// linking and lookup. Other symbols end up only in the local symbol table of</span>
<span class="doccomment">/// the file. This loosely corresponds to pub and priv functions in Rust.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Armed with this knowledge, we know that our solution for address to symbol</span>
<span class="doccomment">/// translation will need to consult both the local and dynamic symbol tables.</span>
<span class="doccomment">/// With that in mind, here's our options of translating an address to</span>
<span class="doccomment">/// a symbol.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * Use dladdr(). The original backtrace()-based idea actually uses dladdr()</span>
<span class="doccomment">/// behind the scenes to translate, and this is why backtrace() was not used.</span>
<span class="doccomment">/// Conveniently, this method works fantastically on macOS. It appears dladdr()</span>
<span class="doccomment">/// uses magic to consult the local symbol table, or we're putting everything</span>
<span class="doccomment">/// in the dynamic symbol table anyway. Regardless, for macOS, this is the</span>
<span class="doccomment">/// method used for translation. It's provided by the system and easy to do.o</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Sadly, all other systems have a dladdr() implementation that does not</span>
<span class="doccomment">/// consult the local symbol table. This means that most functions are blank</span>
<span class="doccomment">/// because they don't have symbols. This means that we need another solution.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * Use unw_get_proc_name(). This is part of the libunwind api (not the</span>
<span class="doccomment">/// libgcc_s version of the libunwind api), but involves taking a dependency</span>
<span class="doccomment">/// to libunwind. We may pursue this route in the future if we bundle</span>
<span class="doccomment">/// libunwind, but libunwind was unwieldy enough that it was not chosen at</span>
<span class="doccomment">/// this time to provide this functionality.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * Shell out to a utility like `readelf`. Crazy though it may sound, it's a</span>
<span class="doccomment">/// semi-reasonable solution. The stdlib already knows how to spawn processes,</span>
<span class="doccomment">/// so in theory it could invoke readelf, parse the output, and consult the</span>
<span class="doccomment">/// local/dynamic symbol tables from there. This ended up not getting chosen</span>
<span class="doccomment">/// due to the craziness of the idea plus the advent of the next option.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * Use `libbacktrace`. It turns out that this is a small library bundled in</span>
<span class="doccomment">/// the gcc repository which provides backtrace and symbol translation</span>
<span class="doccomment">/// functionality. All we really need from it is the backtrace functionality,</span>
<span class="doccomment">/// and we only really need this on everything that's not macOS, so this is the</span>
<span class="doccomment">/// chosen route for now.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// In summary, the current situation uses libgcc_s to get a trace of stack</span>
<span class="doccomment">/// pointers, and we use dladdr() or libbacktrace to translate these addresses</span>
<span class="doccomment">/// to symbols. This is a bit of a hokey implementation as-is, but it works for</span>
<span class="doccomment">/// all unix platforms we support right now, so it at least gets the job done.</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="self">self</span>::<span class="ident">tracing</span>::<span class="ident">unwind_backtrace</span>;
<span class="kw">pub</span> <span class="kw">use</span> <span class="self">self</span>::<span class="ident">printing</span>::{<span class="ident">foreach_symbol_fileline</span>, <span class="ident">resolve_symname</span>};
<span class="comment">// tracing impls:</span>
<span class="kw">mod</span> <span class="ident">tracing</span>;
<span class="comment">// symbol resolvers:</span>
<span class="kw">mod</span> <span class="ident">printing</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">not</span>(<span class="ident">target_os</span> <span class="op">=</span> <span class="string">"emscripten"</span>))]</span>
<span class="kw">pub</span> <span class="kw">mod</span> <span class="ident">gnu</span> {
<span class="kw">use</span> <span class="kw">crate</span>::<span class="ident">io</span>;
<span class="kw">use</span> <span class="kw">crate</span>::<span class="ident">fs</span>;
<span class="kw">use</span> <span class="ident">libc</span>::<span class="ident">c_char</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">not</span>(<span class="ident">any</span>(<span class="ident">target_os</span> <span class="op">=</span> <span class="string">"macos"</span>, <span class="ident">target_os</span> <span class="op">=</span> <span class="string">"ios"</span>)))]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">get_executable_filename</span>() <span class="op">-></span> <span class="ident">io</span>::<span class="prelude-ty">Result</span><span class="op"><</span>(<span class="ident">Vec</span><span class="op"><</span><span class="ident">c_char</span><span class="op">></span>, <span class="ident">fs</span>::<span class="ident">File</span>)<span class="op">></span> {
<span class="prelude-val">Err</span>(<span class="ident">io</span>::<span class="ident">Error</span>::<span class="ident">new</span>(<span class="ident">io</span>::<span class="ident">ErrorKind</span>::<span class="ident">Other</span>, <span class="string">"Not implemented"</span>))
}
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">target_os</span> <span class="op">=</span> <span class="string">"macos"</span>, <span class="ident">target_os</span> <span class="op">=</span> <span class="string">"ios"</span>))]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">get_executable_filename</span>() <span class="op">-></span> <span class="ident">io</span>::<span class="prelude-ty">Result</span><span class="op"><</span>(<span class="ident">Vec</span><span class="op"><</span><span class="ident">c_char</span><span class="op">></span>, <span class="ident">fs</span>::<span class="ident">File</span>)<span class="op">></span> {
<span class="kw">use</span> <span class="kw">crate</span>::<span class="ident">env</span>;
<span class="kw">use</span> <span class="kw">crate</span>::<span class="ident">os</span>::<span class="ident">unix</span>::<span class="ident">ffi</span>::<span class="ident">OsStrExt</span>;
<span class="kw">let</span> <span class="ident">filename</span> <span class="op">=</span> <span class="ident">env</span>::<span class="ident">current_exe</span>()<span class="question-mark">?</span>;
<span class="kw">let</span> <span class="ident">file</span> <span class="op">=</span> <span class="ident">fs</span>::<span class="ident">File</span>::<span class="ident">open</span>(<span class="kw-2">&</span><span class="ident">filename</span>)<span class="question-mark">?</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">filename_cstr</span>: <span class="ident">Vec</span><span class="op"><</span><span class="kw">_</span><span class="op">></span> <span class="op">=</span> <span class="ident">filename</span>.<span class="ident">as_os_str</span>().<span class="ident">as_bytes</span>().<span class="ident">iter</span>()
.<span class="ident">map</span>(<span class="op">|</span><span class="kw-2">&</span><span class="ident">x</span><span class="op">|</span> <span class="ident">x</span> <span class="kw">as</span> <span class="ident">c_char</span>).<span class="ident">collect</span>();
<span class="ident">filename_cstr</span>.<span class="ident">push</span>(<span class="number">0</span>); <span class="comment">// Null terminate</span>
<span class="prelude-val">Ok</span>((<span class="ident">filename_cstr</span>, <span class="ident">file</span>))
}
}
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">BacktraceContext</span>;
</pre></div>
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