LLDB  mainline
ProcessLauncherPosixFork.cpp
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1 //===-- ProcessLauncherLinux.cpp --------------------------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
10 #include "lldb/Host/Host.h"
11 #include "lldb/Host/HostProcess.h"
12 #include "lldb/Host/Pipe.h"
14 #include "lldb/Utility/FileSpec.h"
15 #include "lldb/Utility/Log.h"
16 #include "llvm/Support/Errno.h"
17 
18 #include <limits.h>
19 #include <sys/ptrace.h>
20 #include <sys/wait.h>
21 #include <unistd.h>
22 
23 #include <sstream>
24 #include <csignal>
25 
26 #ifdef __ANDROID__
27 #include <android/api-level.h>
28 #define PT_TRACE_ME PTRACE_TRACEME
29 #endif
30 
31 #if defined(__ANDROID_API__) && __ANDROID_API__ < 15
32 #include <linux/personality.h>
33 #elif defined(__linux__)
34 #include <sys/personality.h>
35 #endif
36 
37 using namespace lldb;
38 using namespace lldb_private;
39 
40 static void FixupEnvironment(Environment &env) {
41 #ifdef __ANDROID__
42  // If there is no PATH variable specified inside the environment then set the
43  // path to /system/bin. It is required because the default path used by
44  // execve() is wrong on android.
45  env.try_emplace("PATH", "/system/bin");
46 #endif
47 }
48 
49 static void LLVM_ATTRIBUTE_NORETURN ExitWithError(int error_fd,
50  const char *operation) {
51  int err = errno;
52  llvm::raw_fd_ostream os(error_fd, true);
53  os << operation << " failed: " << llvm::sys::StrError(err);
54  os.flush();
55  _exit(1);
56 }
57 
58 static void DisableASLRIfRequested(int error_fd, const ProcessLaunchInfo &info) {
59 #if defined(__linux__)
60  if (info.GetFlags().Test(lldb::eLaunchFlagDisableASLR)) {
61  const unsigned long personality_get_current = 0xffffffff;
62  int value = personality(personality_get_current);
63  if (value == -1)
64  ExitWithError(error_fd, "personality get");
65 
66  value = personality(ADDR_NO_RANDOMIZE | value);
67  if (value == -1)
68  ExitWithError(error_fd, "personality set");
69  }
70 #endif
71 }
72 
73 static void DupDescriptor(int error_fd, const FileSpec &file_spec, int fd,
74  int flags) {
75  int target_fd = llvm::sys::RetryAfterSignal(-1, ::open,
76  file_spec.GetCString(), flags, 0666);
77 
78  if (target_fd == -1)
79  ExitWithError(error_fd, "DupDescriptor-open");
80 
81  if (target_fd == fd)
82  return;
83 
84  if (::dup2(target_fd, fd) == -1)
85  ExitWithError(error_fd, "DupDescriptor-dup2");
86 
87  ::close(target_fd);
88  return;
89 }
90 
91 static void LLVM_ATTRIBUTE_NORETURN ChildFunc(int error_fd,
92  const ProcessLaunchInfo &info) {
93  if (info.GetFlags().Test(eLaunchFlagLaunchInSeparateProcessGroup)) {
94  if (setpgid(0, 0) != 0)
95  ExitWithError(error_fd, "setpgid");
96  }
97 
98  for (size_t i = 0; i < info.GetNumFileActions(); ++i) {
99  const FileAction &action = *info.GetFileActionAtIndex(i);
100  switch (action.GetAction()) {
101  case FileAction::eFileActionClose:
102  if (close(action.GetFD()) != 0)
103  ExitWithError(error_fd, "close");
104  break;
105  case FileAction::eFileActionDuplicate:
106  if (dup2(action.GetFD(), action.GetActionArgument()) == -1)
107  ExitWithError(error_fd, "dup2");
108  break;
109  case FileAction::eFileActionOpen:
110  DupDescriptor(error_fd, action.GetFileSpec(), action.GetFD(),
111  action.GetActionArgument());
112  break;
113  case FileAction::eFileActionNone:
114  break;
115  }
116  }
117 
118  const char **argv = info.GetArguments().GetConstArgumentVector();
119 
120  // Change working directory
121  if (info.GetWorkingDirectory() &&
122  0 != ::chdir(info.GetWorkingDirectory().GetCString()))
123  ExitWithError(error_fd, "chdir");
124 
125  DisableASLRIfRequested(error_fd, info);
126  Environment env = info.GetEnvironment();
127  FixupEnvironment(env);
128  Environment::Envp envp = env.getEnvp();
129 
130  // Clear the signal mask to prevent the child from being affected by any
131  // masking done by the parent.
132  sigset_t set;
133  if (sigemptyset(&set) != 0 ||
134  pthread_sigmask(SIG_SETMASK, &set, nullptr) != 0)
135  ExitWithError(error_fd, "pthread_sigmask");
136 
137  if (info.GetFlags().Test(eLaunchFlagDebug)) {
138  // Do not inherit setgid powers.
139  if (setgid(getgid()) != 0)
140  ExitWithError(error_fd, "setgid");
141 
142  // HACK:
143  // Close everything besides stdin, stdout, and stderr that has no file
144  // action to avoid leaking. Only do this when debugging, as elsewhere we
145  // actually rely on passing open descriptors to child processes.
146  for (int fd = 3; fd < sysconf(_SC_OPEN_MAX); ++fd)
147  if (!info.GetFileActionForFD(fd) && fd != error_fd)
148  close(fd);
149 
150  // Start tracing this child that is about to exec.
151  if (ptrace(PT_TRACE_ME, 0, nullptr, 0) == -1)
152  ExitWithError(error_fd, "ptrace");
153  }
154 
155  // Execute. We should never return...
156  execve(argv[0], const_cast<char *const *>(argv), envp);
157 
158 #if defined(__linux__)
159  if (errno == ETXTBSY) {
160  // On android M and earlier we can get this error because the adb daemon
161  // can hold a write handle on the executable even after it has finished
162  // uploading it. This state lasts only a short time and happens only when
163  // there are many concurrent adb commands being issued, such as when
164  // running the test suite. (The file remains open when someone does an "adb
165  // shell" command in the fork() child before it has had a chance to exec.)
166  // Since this state should clear up quickly, wait a while and then give it
167  // one more go.
168  usleep(50000);
169  execve(argv[0], const_cast<char *const *>(argv), envp);
170  }
171 #endif
172 
173  // ...unless exec fails. In which case we definitely need to end the child
174  // here.
175  ExitWithError(error_fd, "execve");
176 }
177 
179 ProcessLauncherPosixFork::LaunchProcess(const ProcessLaunchInfo &launch_info,
180  Status &error) {
181  char exe_path[PATH_MAX];
182  launch_info.GetExecutableFile().GetPath(exe_path, sizeof(exe_path));
183 
184  // A pipe used by the child process to report errors.
185  PipePosix pipe;
186  const bool child_processes_inherit = false;
187  error = pipe.CreateNew(child_processes_inherit);
188  if (error.Fail())
189  return HostProcess();
190 
191  ::pid_t pid = ::fork();
192  if (pid == -1) {
193  // Fork failed
194  error.SetErrorStringWithFormatv("Fork failed with error message: {0}",
195  llvm::sys::StrError());
197  }
198  if (pid == 0) {
199  // child process
200  pipe.CloseReadFileDescriptor();
201  ChildFunc(pipe.ReleaseWriteFileDescriptor(), launch_info);
202  }
203 
204  // parent process
205 
206  pipe.CloseWriteFileDescriptor();
207  char buf[1000];
208  int r = read(pipe.GetReadFileDescriptor(), buf, sizeof buf);
209 
210  if (r == 0)
211  return HostProcess(pid); // No error. We're done.
212 
213  error.SetErrorString(buf);
214 
215  llvm::sys::RetryAfterSignal(-1, waitpid, pid, nullptr, 0);
216 
217  return HostProcess();
218 }
Enumerations for broadcasting.
Definition: SBLaunchInfo.h:14
#define LLDB_INVALID_PROCESS_ID
Definition: lldb-defines.h:92
static void FixupEnvironment(Environment &env)
A file utility class.
Definition: FileSpec.h:55
Action GetAction() const
Definition: FileAction.h:38
int usleep(uint32_t useconds)
static void DupDescriptor(int error_fd, const FileSpec &file_spec, int fd, int flags)
bool Test(ValueType bit) const
Test a single flag bit.
Definition: Flags.h:107
static void DisableASLRIfRequested(int error_fd, const ProcessLaunchInfo &info)
void SetErrorString(llvm::StringRef err_str)
Set the current error string to err_str.
Definition: Status.cpp:241
pid_t fork(void)
Environment & GetEnvironment()
Definition: ProcessInfo.h:88
FileSpec & GetExecutableFile()
Definition: ProcessInfo.h:43
const FileAction * GetFileActionForFD(int fd) const
const char * GetCString(bool denormalize=true) const
Definition: FileSpec.cpp:392
static void LLVM_ATTRIBUTE_NORETURN ChildFunc(int error_fd, const ProcessLaunchInfo &info)
const FileSpec & GetFileSpec() const
Definition: FileAction.cpp:31
static void LLVM_ATTRIBUTE_NORETURN ExitWithError(int error_fd, const char *operation)
bool Fail() const
Test for error condition.
Definition: Status.cpp:181
const FileSpec & GetWorkingDirectory() const
Definition: SBAddress.h:15
uint64_t pid_t
Definition: lldb-types.h:85
#define PATH_MAX
void SetErrorStringWithFormatv(const char *format, Args &&... args)
Definition: Status.h:185
const char ** GetConstArgumentVector() const
Gets the argument vector.
Definition: Args.cpp:278
int GetActionArgument() const
Definition: FileAction.h:40
const FileAction * GetFileActionAtIndex(size_t idx) const
size_t GetPath(char *path, size_t max_path_length, bool denormalize=true) const
Extract the full path to the file.
Definition: FileSpec.cpp:376
An error handling class.
Definition: Status.h:44