[libcxx-commits] [libcxx] WIP - [libc++][debugging] P2546R5: Debugging support & P2810R4: `is_debugger_present` `is_replaceable` (PR #81447)

[Jonathan Wakely via libcxx-commits]

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@@ -0,0 +1,184 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include <__assert>
+#include <__config>
+#include <debugging>
+
+#if defined(_LIBCPP_WIN32API)
+#  define WIN32_LEAN_AND_MEAN
+#  define NOMINMAX
+#  include <windows.h>
+#else
+#  include <csignal>
+#endif
+
+#if defined(_AIX)
+#  include <charconv>
+#  include <cstring>
+#  include <fcntl.h>
+#  include <sys/mman.h>
+#  include <sys/proc.h>
+#  include <sys/procfs.h>
+#  include <sys/types.h>
+#  include <unistd.h>
+#elif defined(__APPLE__) || defined(__FreeBSD__)
+#  if defined(__FreeBSD__) // Include order matters.
+#    include <libutil.h>
+#    include <sys/param.h>
+#    include <sys/proc.h>
+#    include <sys/user.h>
+#  endif // defined(__FreeBSD__)
+#  include <array>
+#  include <sys/sysctl.h>
+#  include <sys/types.h>
+#  include <unistd.h>
+#elif defined(__linux__)
+#  include <cstdio>
+#  include <cstdlib>
+#  include <cstring>
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+// `breakpoint()` implementation
+
+_LIBCPP_EXPORTED_FROM_ABI void __breakpoint() noexcept {
+#if defined(_LIBCPP_WIN32API)
+  DebugBreak();
+#else
+  raise(SIGTRAP);
+#endif // defined(_LIBCPP_WIN32API)
+}
+
+// `is_debugger_present()` implementation
+
+#if defined(_LIBCPP_WIN32API)
+
+static bool __is_debugger_present() noexcept { return IsDebuggerPresent(); }
+
+#elif defined(_AIX)
+
+static bool __is_debugger_present() noexcept {
+  // Get the status information of a process by memory mapping the file /proc/PID/status.
+  // https://www.ibm.com/docs/en/aix/7.3?topic=files-proc-file
+  char __filename[] = "/proc/4294967295/status";
+  if (auto [__ptr, __ec] = to_chars(__filename + 6, __filename + 16, getpid()); __ec == errc()) {
+    strcpy(__ptr, "/status");
+  } else {
+    _LIBCPP_ASSERT_INTERNAL(false, "Could not convert pid to cstring.");
+    return false;
+  }
+
+  int __fd = open(__filename, O_RDONLY);
+  if (__fd < 0) {
+    _LIBCPP_ASSERT_INTERNAL(false, "Could not open '/proc/{pid}/status' for reading.");
+    return false;
+  }
+
+  pstatus_t __status;
+  if (read(__fd, &__status, sizeof(pstatus_t)) < static_cast<ssize_t>(sizeof(pstatus_t))) {
+    _LIBCPP_ASSERT_INTERNAL(false, "Could not read from '/proc/{pid}/status'.");
+    return false;
+  }
+
+  if (__status.pr_flag & STRC)
+    return true;
+
+  return false;
+}
+
+#elif defined(__APPLE__) || defined(__FreeBSD__)
+
+// Returns true if the current process is being debugged (either
+// running under the debugger or has a debugger attached post facto).
+static bool __is_debugger_present() noexcept {
+  // Technical Q&A QA1361: Detecting the Debugger
+  // https://developer.apple.com/library/archive/qa/qa1361/_index.html
+
+  // Initialize mib, which tells 'sysctl' to fetch the information about the current process.
+
+  array __mib{CTL_KERN, KERN_PROC, KERN_PROC_PID, getpid()};
+
+  // Initialize the flags so that, if 'sysctl' fails for some bizarre
+  // reason, we get a predictable result.
+
+  struct kinfo_proc __info {};
+
+  // Call sysctl.
+  // https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man3/sysctl.3.html
+
+  size_t __info_size = sizeof(__info);
+  if (sysctl(__mib.data(), __mib.size(), &__info, &__info_size, nullptr, 0) != 0) {
+    _LIBCPP_ASSERT_INTERNAL(false, "'sysctl' runtime error");
+    return false;
+  }
+
+  // If the process is being debugged if the 'P_TRACED' flag is set.
+  // https://github.com/freebsd/freebsd-src/blob/7f3184ba797452703904d33377dada5f0f8eae96/sys/sys/proc.h#L822
+
+#  if defined(__FreeBSD__)
+  const auto __p_flag = __info.ki_flag;
+#  else // __APPLE__
+  const auto __p_flag = __info.kp_proc.p_flag;
+#  endif
+
+  return ((__p_flag & P_TRACED) != 0);
+}
+
+#elif defined(__linux__)
+
+static bool __is_debugger_present() noexcept {
+#  if defined(_LIBCPP_HAS_NO_FILESYSTEM)
+  _LIBCPP_ASSERT_INTERNAL(false,
+                          "Function is not available. Could not open '/proc/self/status' for reading, libc++ was "
+                          "compiled with _LIBCPP_HAS_NO_FILESYSTEM.");
+  return false;
+#  else
+  // https://docs.kernel.org/filesystems/proc.html
+
+  // Get the status information of a process by reading the file /proc/PID/status.
+  // The link 'self' points to the process reading the file system.
+  FILE* __proc_status_fp = fopen("/proc/self/status", "r");
+  if (__proc_status_fp == nullptr) {
+    _LIBCPP_ASSERT_INTERNAL(false, "Could not open '/proc/self/status' for reading.");
+    return false;
+  }
+
+  char* __line               = nullptr;
+  size_t __lineLen           = 0;
+  const char* __tokenStr     = "TracerPid:";
+  bool __is_debugger_present = false;
+
+  while ((getline(&__line, &__lineLen, __proc_status_fp)) != -1) {
+    // If the process is being debugged "TracerPid"'s value is non-zero.
+    char* __tokenPos = strstr(__line, __tokenStr);
+    if (__tokenPos == nullptr) {
+      continue;
+    }
+
+    __is_debugger_present = (atoi(__tokenPos + strlen(__tokenStr)) != 0);
+    break;
+  }
+
+  free(__line);
+  fclose(__proc_status_fp);
+
+  return __is_debugger_present;
----------------
jwakely wrote:

`atoi(__tokenPos + strlen(__tokenStr))` gives you the tracer's PID so you can use `/proc/{pid}` again to find its details (although not 100% reliably if the executable has been removed from the filesystem, or the tracer process modified its `argv[0]`).

https://github.com/llvm/llvm-project/pull/81447