util: add debug utility

rx/CMakeLists.txt

@@ -4,6 +4,7 @@ find_package(Git)
 
 
 add_library(${PROJECT_NAME} OBJECT
+    src/debug.cpp
     src/die.cpp
     src/hexdump.cpp
     src/mem.cpp

rx/include/rx/debug.hpp

@@ -0,0 +1,9 @@
+#pragma once
+
+namespace rx {
+bool isDebuggerPresent();
+void waitForDebugger();
+void runDebugger();
+void breakpoint();
+void breakpointIfDebugging();
+} // namespace rx

rx/src/debug.cpp

@@ -0,0 +1,101 @@
+#include "debug.hpp"
+#include <fstream>
+#include <list>
+#include <print>
+#include <thread>
+#include <vector>
+
+#ifdef __GNUC__
+#include <linux/limits.h>
+#include <sys/ptrace.h>
+#include <unistd.h>
+
+bool rx::isDebuggerPresent() {
+  std::ifstream in("/proc/self/status");
+  std::string line;
+  while (std::getline(in, line)) {
+    const std::string_view tracerPrefix = "TracerPid:\t";
+
+    if (!line.starts_with(tracerPrefix)) {
+      continue;
+    }
+
+    std::string_view tracer = line;
+    tracer.remove_prefix(tracerPrefix.size());
+
+    if (tracer.size() == 1 && tracer[0] == '0')
+      return false;
+
+    return true;
+  }
+
+  return false;
+}
+
+void rx::waitForDebugger() {
+  if (isDebuggerPresent()) {
+    return;
+  }
+
+  std::println(stderr, "waiting for debugger, pid {}", ::getpid());
+
+  while (!isDebuggerPresent()) {
+    std::this_thread::sleep_for(std::chrono::seconds(1));
+  }
+
+  std::println(stderr, "debugger was attached");
+  std::this_thread::sleep_for(std::chrono::seconds(3));
+  breakpoint();
+}
+
+void rx::runDebugger() {
+  int pid = ::getpid();
+  char path[PATH_MAX];
+  ::readlink("/proc/self/exe", path, sizeof(path));
+  if (fork()) {
+    std::this_thread::sleep_for(std::chrono::seconds(1));
+    waitForDebugger();
+    return;
+  }
+
+  auto pidString = std::to_string(pid);
+  const char *gdbPath = "/usr/bin/gdb";
+
+  std::list<std::string> storage;
+  std::vector<const char *> argv;
+  argv.push_back(gdbPath);
+  argv.push_back(path);
+  argv.push_back(pidString.c_str());
+  argv.push_back("-iex");
+  argv.push_back("set pagination off");
+  argv.push_back("-ex");
+  argv.push_back("handle SIGSYS nostop noprint");
+  argv.push_back("-ex");
+  argv.push_back("handle SIGUSR1 nostop noprint");
+  // TODO: collect elfs
+  //   argv.push_back("-ex");
+  //   argv.push_back("add-symbol-file <path to elf> 0x400000");
+  argv.push_back(nullptr);
+
+  execv(gdbPath, (char **)argv.data());
+}
+
+#else
+bool rx::isDebuggerPresent() { return false; }
+void rx::waitForDebugger() {}
+void rx::runDebugger() {}
+#endif
+
+void rx::breakpoint() {
+#if __has_builtin(__builtin_debugtrap)
+  __builtin_debugtrap();
+#elif defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
+  __asm__ volatile("int3");
+#endif
+}
+
+void rx::breakpointIfDebugging() {
+  if (isDebuggerPresent()) {
+    breakpoint();
+  }
+}