1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #include "base/debug/debugger.h"
6 
7 #include <errno.h>
8 #include <fcntl.h>
9 #include <stddef.h>
10 #include <stdio.h>
11 #include <stdlib.h>
12 #include <sys/param.h>
13 #include <sys/stat.h>
14 #include <sys/types.h>
15 #include <unistd.h>
16 
17 #include <memory>
18 #include <vector>
19 
20 #include "base/check_op.h"
21 #include "base/clang_profiling_buildflags.h"
22 #include "base/notreached.h"
23 #include "base/stl_util.h"
24 #include "base/strings/string_util.h"
25 #include "base/threading/platform_thread.h"
26 #include "base/time/time.h"
27 #include "build/build_config.h"
28 
29 #if defined(__GLIBCXX__)
30 #include <cxxabi.h>
31 #endif
32 
33 #if defined(OS_APPLE)
34 #include <AvailabilityMacros.h>
35 #endif
36 
37 #if defined(OS_APPLE) || defined(OS_BSD)
38 #include <sys/sysctl.h>
39 #endif
40 
41 #if defined(OS_FREEBSD) || defined(OS_DRAGONFLY)
42 #include <sys/user.h>
43 #endif
44 
45 #if defined(OS_FUCHSIA)
46 #include <zircon/process.h>
47 #include <zircon/syscalls.h>
48 #endif
49 
50 #include <ostream>
51 
52 #include "base/check.h"
53 #include "base/debug/alias.h"
54 #include "base/debug/debugging_buildflags.h"
55 #include "base/environment.h"
56 #include "base/files/file_util.h"
57 #include "base/posix/eintr_wrapper.h"
58 #include "base/process/process.h"
59 #include "base/strings/string_number_conversions.h"
60 #include "base/strings/string_piece.h"
61 
62 #if BUILDFLAG(CLANG_PROFILING)
63 #include "base/test/clang_profiling.h"
64 #endif
65 
66 #if defined(USE_SYMBOLIZE)
67 #include "base/third_party/symbolize/symbolize.h"
68 #endif
69 
70 namespace base {
71 namespace debug {
72 
73 #if defined(OS_APPLE) || defined(OS_BSD)
74 
75 // Based on Apple's recommended method as described in
76 // http://developer.apple.com/qa/qa2004/qa1361.html
BeingDebugged()77 bool BeingDebugged() {
78   // NOTE: This code MUST be async-signal safe (it's used by in-process
79   // stack dumping signal handler). NO malloc or stdio is allowed here.
80   //
81   // While some code used below may be async-signal unsafe, note how
82   // the result is cached (see |is_set| and |being_debugged| static variables
83   // right below). If this code is properly warmed-up early
84   // in the start-up process, it should be safe to use later.
85 
86   // If the process is sandboxed then we can't use the sysctl, so cache the
87   // value.
88   static bool is_set = false;
89   static bool being_debugged = false;
90 
91   if (is_set)
92     return being_debugged;
93 
94   // Initialize mib, which tells sysctl what info we want.  In this case,
95   // we're looking for information about a specific process ID.
96   int mib[] = {
97     CTL_KERN,
98     KERN_PROC,
99     KERN_PROC_PID,
100     getpid()
101 #if defined(OS_BSD)
102     , sizeof(struct kinfo_proc),
103     0
104 #endif
105   };
106 
107   // Caution: struct kinfo_proc is marked __APPLE_API_UNSTABLE.  The source and
108   // binary interfaces may change.
109   struct kinfo_proc *info;
110   size_t info_size;
111 
112   if (sysctl(mib, base::size(mib), NULL, &info_size, NULL, 0) < 0)
113     return -1;
114 
115   info = (struct kinfo_proc *)malloc(info_size);
116   mib[5] = (info_size / sizeof(struct kinfo_proc));
117 
118   int sysctl_result = sysctl(mib, base::size(mib), info, &info_size, NULL, 0);
119   DCHECK_EQ(sysctl_result, 0);
120   if (sysctl_result != 0) {
121     is_set = true;
122     being_debugged = false;
123     goto out;
124   }
125 
126   // This process is being debugged if the P_TRACED flag is set.
127   is_set = true;
128 #if defined(OS_FREEBSD)
129   being_debugged = (info->ki_flag & P_TRACED) != 0;
130 #elif defined(OS_DRAGONFLY)
131   being_debugged = (info->kp_flags & P_TRACED) != 0;
132 #elif defined(OS_BSD)
133   being_debugged = (info->p_flag & P_TRACED) != 0;
134 #else
135   being_debugged = (info->kp_proc.p_flag & P_TRACED) != 0;
136 #endif
137 
138 out:
139   free(info);
140   return being_debugged;
141 }
142 
VerifyDebugger()143 void VerifyDebugger() {
144 #if BUILDFLAG(ENABLE_LLDBINIT_WARNING)
145   if (Environment::Create()->HasVar("CHROMIUM_LLDBINIT_SOURCED"))
146     return;
147   if (!BeingDebugged())
148     return;
149   DCHECK(false)
150       << "Detected lldb without sourcing //tools/lldb/lldbinit.py. lldb may "
151          "not be able to find debug symbols. Please see debug instructions for "
152          "using //tools/lldb/lldbinit.py:\n"
153          "https://chromium.googlesource.com/chromium/src/+/master/docs/"
154          "lldbinit.md\n"
155          "To continue anyway, type 'continue' in lldb. To always skip this "
156          "check, define an environment variable CHROMIUM_LLDBINIT_SOURCED=1";
157 #endif
158 }
159 
160 #elif defined(OS_LINUX) || defined(OS_CHROMEOS) || defined(OS_ANDROID) || \
161     defined(OS_AIX)
162 
163 // We can look in /proc/self/status for TracerPid.  We are likely used in crash
164 // handling, so we are careful not to use the heap or have side effects.
165 // Another option that is common is to try to ptrace yourself, but then we
166 // can't detach without forking(), and that's not so great.
167 // static
168 Process GetDebuggerProcess() {
169   // NOTE: This code MUST be async-signal safe (it's used by in-process
170   // stack dumping signal handler). NO malloc or stdio is allowed here.
171 
172   int status_fd = open("/proc/self/status", O_RDONLY);
173   if (status_fd == -1)
174     return Process();
175 
176   // We assume our line will be in the first 1024 characters and that we can
177   // read this much all at once.  In practice this will generally be true.
178   // This simplifies and speeds up things considerably.
179   char buf[1024];
180 
181   ssize_t num_read = HANDLE_EINTR(read(status_fd, buf, sizeof(buf)));
182   if (IGNORE_EINTR(close(status_fd)) < 0)
183     return Process();
184 
185   if (num_read <= 0)
186     return Process();
187 
188   StringPiece status(buf, num_read);
189   StringPiece tracer("TracerPid:\t");
190 
191   StringPiece::size_type pid_index = status.find(tracer);
192   if (pid_index == StringPiece::npos)
193     return Process();
194   pid_index += tracer.size();
195   StringPiece::size_type pid_end_index = status.find('\n', pid_index);
196   if (pid_end_index == StringPiece::npos)
197     return Process();
198 
199   StringPiece pid_str(buf + pid_index, pid_end_index - pid_index);
200   int pid = 0;
201   if (!StringToInt(pid_str, &pid))
202     return Process();
203 
204   return Process(pid);
205 }
206 
207 bool BeingDebugged() {
208   return GetDebuggerProcess().IsValid();
209 }
210 
211 void VerifyDebugger() {
212 #if BUILDFLAG(ENABLE_GDBINIT_WARNING)
213   // Quick check before potentially slower GetDebuggerProcess().
214   if (Environment::Create()->HasVar("CHROMIUM_GDBINIT_SOURCED"))
215     return;
216 
217   Process proc = GetDebuggerProcess();
218   if (!proc.IsValid())
219     return;
220 
221   FilePath cmdline_file =
222       FilePath("/proc").Append(NumberToString(proc.Handle())).Append("cmdline");
223   std::string cmdline;
224   if (!ReadFileToString(cmdline_file, &cmdline))
225     return;
226 
227   // /proc/*/cmdline separates arguments with null bytes, but we only care about
228   // the executable name, so interpret |cmdline| as a null-terminated C string
229   // to extract the exe portion.
230   StringPiece exe(cmdline.c_str());
231 
232   DCHECK(ToLowerASCII(exe).find("gdb") == std::string::npos)
233       << "Detected gdb without sourcing //tools/gdb/gdbinit.  gdb may not be "
234          "able to find debug symbols, and pretty-printing of STL types may not "
235          "work.  Please see debug instructions for using //tools/gdb/gdbinit:\n"
236          "https://chromium.googlesource.com/chromium/src/+/master/docs/"
237          "gdbinit.md\n"
238          "To continue anyway, type 'continue' in gdb.  To always skip this "
239          "check, define an environment variable CHROMIUM_GDBINIT_SOURCED=1";
240 #endif
241 }
242 
243 #elif defined(OS_FUCHSIA)
244 
245 bool BeingDebugged() {
246   zx_info_process_t info = {};
247   // Ignore failures. The 0-initialization above will result in "false" for
248   // error cases.
249   zx_object_get_info(zx_process_self(), ZX_INFO_PROCESS, &info, sizeof(info),
250                      nullptr, nullptr);
251   return info.debugger_attached;
252 }
253 
254 void VerifyDebugger() {}
255 
256 #else
257 
258 bool BeingDebugged() {
259   NOTIMPLEMENTED();
260   return false;
261 }
262 
263 void VerifyDebugger() {}
264 
265 #endif
266 
267 // We want to break into the debugger in Debug mode, and cause a crash dump in
268 // Release mode. Breakpad behaves as follows:
269 //
270 // +-------+-----------------+-----------------+
271 // | OS    | Dump on SIGTRAP | Dump on SIGABRT |
272 // +-------+-----------------+-----------------+
273 // | Linux |       N         |        Y        |
274 // | Mac   |       Y         |        N        |
275 // +-------+-----------------+-----------------+
276 //
277 // Thus we do the following:
278 // Linux: Debug mode if a debugger is attached, send SIGTRAP; otherwise send
279 //        SIGABRT
280 // Mac: Always send SIGTRAP.
281 
282 #if defined(ARCH_CPU_ARMEL)
283 #define DEBUG_BREAK_ASM() asm("bkpt 0")
284 #elif defined(ARCH_CPU_ARM64)
285 #define DEBUG_BREAK_ASM() asm("brk 0")
286 #elif defined(ARCH_CPU_MIPS_FAMILY)
287 #define DEBUG_BREAK_ASM() asm("break 2")
288 #elif defined(ARCH_CPU_X86_FAMILY)
289 #define DEBUG_BREAK_ASM() asm("int3")
290 #endif
291 
292 #if defined(NDEBUG) && !defined(OS_APPLE) && !defined(OS_ANDROID)
293 #define DEBUG_BREAK() abort()
294 #elif defined(OS_NACL)
295 // The NaCl verifier doesn't let use use int3.  For now, we call abort().  We
296 // should ask for advice from some NaCl experts about the optimum thing here.
297 // http://code.google.com/p/nativeclient/issues/detail?id=645
298 #define DEBUG_BREAK() abort()
299 #elif !defined(OS_APPLE)
300 // Though Android has a "helpful" process called debuggerd to catch native
301 // signals on the general assumption that they are fatal errors. If no debugger
302 // is attached, we call abort since Breakpad needs SIGABRT to create a dump.
303 // When debugger is attached, for ARM platform the bkpt instruction appears
304 // to cause SIGBUS which is trapped by debuggerd, and we've had great
305 // difficulty continuing in a debugger once we stop from SIG triggered by native
306 // code, use GDB to set |go| to 1 to resume execution; for X86 platform, use
307 // "int3" to setup breakpiont and raise SIGTRAP.
308 //
309 // On other POSIX architectures, except Mac OS X, we use the same logic to
310 // ensure that breakpad creates a dump on crashes while it is still possible to
311 // use a debugger.
312 namespace {
DebugBreak()313 void DebugBreak() {
314   if (!BeingDebugged()) {
315     abort();
316   } else {
317 #if defined(DEBUG_BREAK_ASM)
318     DEBUG_BREAK_ASM();
319 #else
320     volatile int go = 0;
321     while (!go)
322       PlatformThread::Sleep(TimeDelta::FromMilliseconds(100));
323 #endif
324   }
325 }
326 }  // namespace
327 #define DEBUG_BREAK() DebugBreak()
328 #elif defined(DEBUG_BREAK_ASM)
329 #define DEBUG_BREAK() DEBUG_BREAK_ASM()
330 #else
331 #error "Don't know how to debug break on this architecture/OS"
332 #endif
333 
BreakDebugger()334 void BreakDebugger() {
335 #if BUILDFLAG(CLANG_PROFILING)
336   WriteClangProfilingProfile();
337 #endif
338 
339   // NOTE: This code MUST be async-signal safe (it's used by in-process
340   // stack dumping signal handler). NO malloc or stdio is allowed here.
341 
342   // Linker's ICF feature may merge this function with other functions with the
343   // same definition (e.g. any function whose sole job is to call abort()) and
344   // it may confuse the crash report processing system. http://crbug.com/508489
345   static int static_variable_to_make_this_function_unique = 0;
346   Alias(&static_variable_to_make_this_function_unique);
347 
348   DEBUG_BREAK();
349 #if defined(OS_ANDROID) && !defined(OFFICIAL_BUILD)
350   // For Android development we always build release (debug builds are
351   // unmanageably large), so the unofficial build is used for debugging. It is
352   // helpful to be able to insert BreakDebugger() statements in the source,
353   // attach the debugger, inspect the state of the program and then resume it by
354   // setting the 'go' variable above.
355 #elif defined(NDEBUG)
356   // Terminate the program after signaling the debug break.
357   // When DEBUG_BREAK() expands to abort(), this is unreachable code. Rather
358   // than carefully tracking in which cases DEBUG_BREAK()s is noreturn, just
359   // disable the unreachable code warning here.
360 #pragma GCC diagnostic push
361 #pragma GCC diagnostic ignored "-Wunreachable-code"
362   _exit(1);
363 #pragma GCC diagnostic pop
364 #endif
365 }
366 
367 }  // namespace debug
368 }  // namespace base
369