Transform ProcessLauncherLinux to ProcessLauncherPosixFork

Summary:
Use ProcessLauncherPosixFork in Linux and NetBSD.

Changes to ProcessLauncherLinux:
 - Limit personality.h and ASLR code to Linux.
 - Reuse portable ptrace(2) PT_TRACE_ME operation available on Linux and BSDs.
 - Limit ETXTBSY error path from execve(2) to Linux.
 - In LaunchProcess declaration change virtual to override.

This code should be readily available for FreeBSD.

Sponsored by <The NetBSD Foundation>

Reviewers: joerg, clayborg, labath, emaste

Reviewed By: labath

Subscribers: danalbert, srhines, mgorny, #lldb

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D29347

llvm-svn: 293768

1 files changed, 231 insertions, 0 deletions

diff --git a/lldb/source/Host/posix/ProcessLauncherPosixFork.cpp b/lldb/source/Host/posix/ProcessLauncherPosixFork.cpp
new file mode 100644
index 00000000000..c46bb2f514b
--- /dev/null
+++ b/lldb/source/Host/posix/ProcessLauncherPosixFork.cpp
@@ -0,0 +1,231 @@
+//===-- ProcessLauncherLinux.cpp --------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "lldb/Host/posix/ProcessLauncherPosixFork.h"
+#include "lldb/Core/Log.h"
+#include "lldb/Host/FileSpec.h"
+#include "lldb/Host/Host.h"
+#include "lldb/Host/HostProcess.h"
+#include "lldb/Host/Pipe.h"
+#include "lldb/Target/ProcessLaunchInfo.h"
+
+#include <limits.h>
+#include <sys/ptrace.h>
+#include <sys/wait.h>
+
+#include <sstream>
+
+#ifdef __ANDROID__
+#include <android/api-level.h>
+#endif
+
+#if defined(__ANDROID_API__) && __ANDROID_API__ < 21
+#include <linux/personality.h>
+#elif defined(__linux__)
+#include <sys/personality.h>
+#endif
+
+using namespace lldb;
+using namespace lldb_private;
+
+static void FixupEnvironment(Args &env) {
+#ifdef __ANDROID__
+  // If there is no PATH variable specified inside the environment then set the
+  // path to /system/bin. It is required because the default path used by
+  // execve() is wrong on android.
+  static const char *path = "PATH=";
+  for (auto &entry : env.entries()) {
+    if (entry.ref.startswith(path))
+      return;
+  }
+  env.AppendArgument(llvm::StringRef("PATH=/system/bin"));
+#endif
+}
+
+static void LLVM_ATTRIBUTE_NORETURN ExitWithError(int error_fd,
+                                                  const char *operation) {
+  std::ostringstream os;
+  os << operation << " failed: " << strerror(errno);
+  write(error_fd, os.str().data(), os.str().size());
+  close(error_fd);
+  _exit(1);
+}
+
+static void DisableASLRIfRequested(int error_fd, const ProcessLaunchInfo &info) {
+#if defined(__linux__)
+  if (info.GetFlags().Test(lldb::eLaunchFlagDisableASLR)) {
+    const unsigned long personality_get_current = 0xffffffff;
+    int value = personality(personality_get_current);
+    if (value == -1)
+      ExitWithError(error_fd, "personality get");
+
+    value = personality(ADDR_NO_RANDOMIZE | value);
+    if (value == -1)
+      ExitWithError(error_fd, "personality set");
+  }
+#endif
+}
+
+static void DupDescriptor(int error_fd, const FileSpec &file_spec, int fd,
+                          int flags) {
+  int target_fd = ::open(file_spec.GetCString(), flags, 0666);
+
+  if (target_fd == -1)
+    ExitWithError(error_fd, "DupDescriptor-open");
+
+  if (target_fd == fd)
+    return;
+
+  if (::dup2(target_fd, fd) == -1)
+    ExitWithError(error_fd, "DupDescriptor-dup2");
+
+  ::close(target_fd);
+  return;
+}
+
+static void LLVM_ATTRIBUTE_NORETURN ChildFunc(int error_fd,
+                                              const ProcessLaunchInfo &info) {
+  // First, make sure we disable all logging. If we are logging to stdout, our
+  // logs can be
+  // mistaken for inferior output.
+  Log::DisableAllLogChannels(nullptr);
+
+  // Do not inherit setgid powers.
+  if (setgid(getgid()) != 0)
+    ExitWithError(error_fd, "setgid");
+
+  if (info.GetFlags().Test(eLaunchFlagLaunchInSeparateProcessGroup)) {
+    if (setpgid(0, 0) != 0)
+      ExitWithError(error_fd, "setpgid");
+  }
+
+  for (size_t i = 0; i < info.GetNumFileActions(); ++i) {
+    const FileAction &action = *info.GetFileActionAtIndex(i);
+    switch (action.GetAction()) {
+    case FileAction::eFileActionClose:
+      if (close(action.GetFD()) != 0)
+        ExitWithError(error_fd, "close");
+      break;
+    case FileAction::eFileActionDuplicate:
+      if (dup2(action.GetFD(), action.GetActionArgument()) == -1)
+        ExitWithError(error_fd, "dup2");
+      break;
+    case FileAction::eFileActionOpen:
+      DupDescriptor(error_fd, action.GetFileSpec(), action.GetFD(),
+                    action.GetActionArgument());
+      break;
+    case FileAction::eFileActionNone:
+      break;
+    }
+  }
+
+  const char **argv = info.GetArguments().GetConstArgumentVector();
+
+  // Change working directory
+  if (info.GetWorkingDirectory() &&
+      0 != ::chdir(info.GetWorkingDirectory().GetCString()))
+    ExitWithError(error_fd, "chdir");
+
+  DisableASLRIfRequested(error_fd, info);
+  Args env = info.GetEnvironmentEntries();
+  FixupEnvironment(env);
+  const char **envp = env.GetConstArgumentVector();
+
+  // Clear the signal mask to prevent the child from being affected by
+  // any masking done by the parent.
+  sigset_t set;
+  if (sigemptyset(&set) != 0 ||
+      pthread_sigmask(SIG_SETMASK, &set, nullptr) != 0)
+    ExitWithError(error_fd, "pthread_sigmask");
+
+  if (info.GetFlags().Test(eLaunchFlagDebug)) {
+    // HACK:
+    // Close everything besides stdin, stdout, and stderr that has no file
+    // action to avoid leaking. Only do this when debugging, as elsewhere we
+    // actually rely on
+    // passing open descriptors to child processes.
+    for (int fd = 3; fd < sysconf(_SC_OPEN_MAX); ++fd)
+      if (!info.GetFileActionForFD(fd) && fd != error_fd)
+        close(fd);
+
+    // Start tracing this child that is about to exec.
+    if (ptrace(PT_TRACE_ME, 0, nullptr, 0) == -1)
+      ExitWithError(error_fd, "ptrace");
+  }
+
+  // Execute.  We should never return...
+  execve(argv[0], const_cast<char *const *>(argv),
+         const_cast<char *const *>(envp));
+
+#if defined(__linux__)
+  if (errno == ETXTBSY) {
+    // On android M and earlier we can get this error because the adb deamon can
+    // hold a write
+    // handle on the executable even after it has finished uploading it. This
+    // state lasts
+    // only a short time and happens only when there are many concurrent adb
+    // commands being
+    // issued, such as when running the test suite. (The file remains open when
+    // someone does
+    // an "adb shell" command in the fork() child before it has had a chance to
+    // exec.) Since
+    // this state should clear up quickly, wait a while and then give it one
+    // more go.
+    usleep(50000);
+    execve(argv[0], const_cast<char *const *>(argv),
+           const_cast<char *const *>(envp));
+  }
+#endif
+
+  // ...unless exec fails.  In which case we definitely need to end the child
+  // here.
+  ExitWithError(error_fd, "execve");
+}
+
+HostProcess
+ProcessLauncherPosixFork::LaunchProcess(const ProcessLaunchInfo &launch_info,
+                                        Error &error) {
+  char exe_path[PATH_MAX];
+  launch_info.GetExecutableFile().GetPath(exe_path, sizeof(exe_path));
+
+  // A pipe used by the child process to report errors.
+  PipePosix pipe;
+  const bool child_processes_inherit = false;
+  error = pipe.CreateNew(child_processes_inherit);
+  if (error.Fail())
+    return HostProcess();
+
+  ::pid_t pid = ::fork();
+  if (pid == -1) {
+    // Fork failed
+    error.SetErrorStringWithFormat("Fork failed with error message: %s",
+                                   strerror(errno));
+    return HostProcess(LLDB_INVALID_PROCESS_ID);
+  }
+  if (pid == 0) {
+    // child process
+    pipe.CloseReadFileDescriptor();
+    ChildFunc(pipe.ReleaseWriteFileDescriptor(), launch_info);
+  }
+
+  // parent process
+
+  pipe.CloseWriteFileDescriptor();
+  char buf[1000];
+  int r = read(pipe.GetReadFileDescriptor(), buf, sizeof buf);
+
+  if (r == 0)
+    return HostProcess(pid); // No error. We're done.
+
+  error.SetErrorString(buf);
+
+  waitpid(pid, nullptr, 0);
+
+  return HostProcess();
+}