bt: Add a little backtrace program that uses SymbolServer

Usage: bt <PID>

This program will print a symbolicated backtrace for the main thread of
the process with the given PID. It uses SymbolServer for the
symbolication.

There's a lot of room for improvement in this command, but it is pretty
neat already. :^)

Userland/Utilities/CMakeLists.txt

@@ -17,6 +17,7 @@ endforeach()
 
 target_link_libraries(aplay LibAudio)
 target_link_libraries(avol LibAudio)
+target_link_libraries(bt LibSymbolClient)
 target_link_libraries(checksum LibCrypto)
 target_link_libraries(chres LibGUI)
 target_link_libraries(copy LibGUI)

Userland/Utilities/bt.cpp

@@ -0,0 +1,171 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/JsonArray.h>
+#include <AK/JsonObject.h>
+#include <AK/JsonValue.h>
+#include <AK/LogStream.h>
+#include <LibCore/ArgsParser.h>
+#include <LibCore/EventLoop.h>
+#include <LibCore/File.h>
+#include <LibSymbolClient/Client.h>
+
+int main(int argc, char** argv)
+{
+    if (pledge("stdio rpath unix fattr", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    if (unveil("/proc", "r") < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    if (unveil("/tmp/rpc", "crw") < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    if (unveil("/tmp/portal/symbol", "rw") < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    if (unveil(nullptr, nullptr) < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    Core::ArgsParser args_parser;
+    pid_t pid = 0;
+    args_parser.add_positional_argument(pid, "PID", "pid");
+
+    args_parser.parse(argc, argv);
+
+    struct RegionWithSymbols {
+        FlatPtr base { 0 };
+        size_t size { 0 };
+        String path;
+    };
+
+    Vector<FlatPtr> stack;
+    Vector<RegionWithSymbols> regions;
+
+    {
+        // FIXME: Support multiple threads in the same process!
+        auto stack_path = String::formatted("/proc/{}/stacks/{}", pid, pid);
+        auto file_or_error = Core::File::open(stack_path, Core::IODevice::ReadOnly);
+        if (file_or_error.is_error()) {
+            warnln("Could not open {}: {}", stack_path, file_or_error.error());
+            return 1;
+        }
+
+        auto json = JsonValue::from_string(file_or_error.value()->read_all());
+        if (!json.has_value() || !json.value().is_array()) {
+            warnln("Invalid contents in {}", stack_path);
+            return 1;
+        }
+
+        stack.ensure_capacity(json.value().as_array().size());
+        for (auto& value : json.value().as_array().values()) {
+            stack.append(value.to_u32());
+        }
+    }
+
+    {
+        auto vm_path = String::formatted("/proc/{}/vm", pid);
+        auto file_or_error = Core::File::open(vm_path, Core::IODevice::ReadOnly);
+        if (file_or_error.is_error()) {
+            warnln("Could not open {}: {}", vm_path, file_or_error.error());
+            return 1;
+        }
+
+        auto json = JsonValue::from_string(file_or_error.value()->read_all());
+        if (!json.has_value() || !json.value().is_array()) {
+            warnln("Invalid contents in {}", vm_path);
+            return 1;
+        }
+
+        for (auto& region_value : json.value().as_array().values()) {
+            auto& region = region_value.as_object();
+            auto name = region.get("name").to_string();
+            auto address = region.get("address").to_u32();
+            auto size = region.get("size").to_u32();
+
+            String path;
+            if (name == "/usr/lib/Loader.so") {
+                path = name;
+            } else if (name.ends_with(": .text")) {
+                auto parts = name.split_view(':');
+                path = parts[0];
+                if (!path.starts_with('/'))
+                    path = String::formatted("/usr/lib/{}", path);
+            } else {
+                continue;
+            }
+
+            RegionWithSymbols r;
+            r.base = address;
+            r.size = size;
+            r.path = path;
+            regions.append(move(r));
+        }
+    }
+
+    Core::EventLoop loop;
+
+    auto client = SymbolClient::Client::construct();
+
+    for (auto address : stack) {
+
+        const RegionWithSymbols* found_region = nullptr;
+        for (auto& region : regions) {
+            if (address >= region.base && address < (region.base + region.size)) {
+                found_region = &region;
+                break;
+            }
+        }
+
+        if (!found_region) {
+            outln("{:p}  ??", address);
+            continue;
+        }
+
+        Vector<FlatPtr> addresses;
+        addresses.append(address - found_region->base);
+
+        auto symbols = client->symbolicate(found_region->path, addresses);
+        if (symbols.is_empty()) {
+            outln("{:p}  ??", address);
+            continue;
+        }
+
+        outln("{:p}  {}", address, symbols[0].name);
+    }
+
+    return 0;
+}