[Backtracing][Linux] Add Linux crash handler to the runtime.

This also adds a function to demangle a symbol, and a way for the
backtracing code to report warning messages to the same place as
the main runtime.

I'd like to rename the _swift_isThunkFunction() SPI also, but we
can't do that until we've made the changes to the _Backtracing
library, so we'll do that there instead.

rdar://110261430

Author: al45tair

include/swift/Runtime/Backtrace.h

@@ -17,10 +17,17 @@
 #ifndef SWIFT_RUNTIME_BACKTRACE_H
 #define SWIFT_RUNTIME_BACKTRACE_H
 
+#ifdef __linux__
+#include <sys/types.h>
+#include <sys/wait.h>
+
+#include <signal.h>
+#endif // defined(__linux__)
+
 #include "swift/Runtime/Config.h"
+#include "swift/Runtime/CrashInfo.h"
 
 #include "swift/shims/Visibility.h"
-#include "swift/shims/CrashInfo.h"
 
 #include <inttypes.h>
 
@@ -50,7 +57,11 @@ typedef int ErrorCode;
 
 SWIFT_RUNTIME_STDLIB_INTERNAL ErrorCode _swift_installCrashHandler();
 
+#ifdef __linux__
+SWIFT_RUNTIME_STDLIB_INTERNAL bool _swift_spawnBacktracer(const ArgChar * const *argv, int memserver_fd);
+#else
 SWIFT_RUNTIME_STDLIB_INTERNAL bool _swift_spawnBacktracer(const ArgChar * const *argv);
+#endif
 
 enum class UnwindAlgorithm {
   Auto = 0,
@@ -125,6 +136,12 @@ SWIFT_RUNTIME_STDLIB_INTERNAL BacktraceSettings _swift_backtraceSettings;
 
 SWIFT_RUNTIME_STDLIB_SPI SWIFT_CC(swift) bool _swift_isThunkFunction(const char *mangledName);
 
+SWIFT_RUNTIME_STDLIB_SPI
+char *_swift_backtrace_demangle(const char *mangledName,
+                                size_t mangledNameLength,
+                                char *outputBuffer,
+                                size_t *outputBufferSize,
+                                int *status);
 #ifdef __cplusplus
 } // namespace backtrace
 } // namespace runtime

include/swift/Runtime/Debug.h

@@ -124,6 +124,9 @@ swift_dynamicCastFailure(const void *sourceType, const char *sourceName,
 SWIFT_RUNTIME_EXPORT
 void swift_reportError(uint32_t flags, const char *message);
 
+SWIFT_RUNTIME_EXPORT
+void swift_reportWarning(uint32_t flags, const char *message);
+
 // Halt due to an overflow in swift_retain().
 SWIFT_RUNTIME_ATTRIBUTE_NORETURN SWIFT_RUNTIME_ATTRIBUTE_NOINLINE
 void swift_abortRetainOverflow();

stdlib/public/runtime/Backtrace.cpp

@@ -52,6 +52,12 @@
 #include <cstring>
 #include <cerrno>
 
+#ifdef _WIN32
+// We'll probably want dbghelp.h here
+#else
+#include <cxxabi.h>
+#endif
+
 #define DEBUG_BACKTRACING_SETTINGS 0
 
 #ifndef lengthof
@@ -70,7 +76,7 @@ SWIFT_RUNTIME_STDLIB_INTERNAL BacktraceSettings _swift_backtraceSettings = {
   // enabled
 #if TARGET_OS_OSX
   OnOffTty::TTY,
-#elif 0 // defined(__linux__) || defined(_WIN32)
+#elif defined(__linux__) // || defined(_WIN32)
   OnOffTty::On,
 #else
   OnOffTty::Off,
@@ -80,7 +86,7 @@ SWIFT_RUNTIME_STDLIB_INTERNAL BacktraceSettings _swift_backtraceSettings = {
   true,
 
   // interactive
-#if TARGET_OS_OSX // || defined(__linux__) || defined(_WIN32)
+#if TARGET_OS_OSX || defined(__linux__) // || defined(_WIN32)
   OnOffTty::TTY,
 #else
   OnOffTty::Off,
@@ -773,6 +779,54 @@ _swift_backtraceSetupEnvironment()
   *penv = 0;
 }
 
+#ifdef __linux__
+struct spawn_info {
+  const char *path;
+  char * const *argv;
+  char * const *envp;
+  int memserver;
+};
+
+uint8_t spawn_stack[4096];
+
+int
+do_spawn(void *ptr) {
+  struct spawn_info *pinfo = (struct spawn_info *)ptr;
+
+  /* Ensure that the memory server is always on fd 4 */
+  if (pinfo->memserver != 4) {
+    dup2(pinfo->memserver, 4);
+    close(pinfo->memserver);
+  }
+
+  /* Clear the signal mask */
+  sigset_t mask;
+  sigfillset(&mask);
+  sigprocmask(SIG_UNBLOCK, &mask, NULL);
+
+  return execvpe(pinfo->path, pinfo->argv, pinfo->envp);
+}
+
+int
+safe_spawn(pid_t *ppid, const char *path, int memserver,
+           char * const argv[], char * const envp[])
+{
+  struct spawn_info info = { path, argv, envp, memserver };
+
+  /* The CLONE_VFORK is *required* because info is on the stack; we don't
+     want to return until *after* the subprocess has called execvpe(). */
+  int ret = clone(do_spawn, spawn_stack + sizeof(spawn_stack),
+                  CLONE_VFORK|CLONE_VM, &info);
+  if (ret < 0)
+    return ret;
+
+  close(memserver);
+
+  *ppid = ret;
+  return 0;
+}
+#endif // defined(__linux__)
+
 #endif // SWIFT_BACKTRACE_ON_CRASH_SUPPORTED
 
 } // namespace
@@ -796,13 +850,109 @@ _swift_isThunkFunction(const char *mangledName) {
   return ctx.isThunkSymbol(mangledName);
 }
 
+/// Try to demangle a symbol.
+///
+/// Unlike other entry points that do this, we try both Swift and C++ here.
+///
+/// @param mangledName is the symbol name to be demangled.
+/// @param mangledNameLength is the length of this name.
+/// @param outputBuffer is a pointer to a buffer in which to place the result.
+/// @param outputBufferSize points to a variable that will be filled in with
+/// the size of the allocated buffer (NOT the length of the result).
+/// @param status returns the status codes defined in the C++ ABI.
+///
+/// If outputBuffer and outputBufferSize are both nullptr, this function will
+/// allocate memory for the result using malloc().
+///
+/// If outputBuffer is nullptr but outputBufferSize is not, the function will
+/// fill outputBufferSize with the required buffer size and return nullptr.
+///
+/// Otherwise, the result will be written into the output buffer, and the
+/// size of the result will be written into outputBufferSize.  If the buffer
+/// is too small, the result will be truncated, but outputBufferSize will
+/// still be set to the number of bytes that would have been required to
+/// copy out the full result (including a trailing NUL).
+///
+/// @returns `true` if demangling was successful.
+SWIFT_RUNTIME_STDLIB_SPI char *
+_swift_backtrace_demangle(const char *mangledName,
+                          size_t mangledNameLength,
+                          char *outputBuffer,
+                          size_t *outputBufferSize,
+                          int *status) {
+  llvm::StringRef name = llvm::StringRef(mangledName, mangledNameLength);
+
+  if (Demangle::isSwiftSymbol(name)) {
+    // This is a Swift mangling
+    auto options = DemangleOptions::SimplifiedUIDemangleOptions();
+    auto result = Demangle::demangleSymbolAsString(name, options);
+    size_t bufferSize;
+
+    if (outputBufferSize) {
+      bufferSize = *outputBufferSize;
+      *outputBufferSize = result.length() + 1;
+    }
+
+    if (outputBuffer == nullptr) {
+      outputBuffer = (char *)::malloc(result.length() + 1);
+      bufferSize = result.length() + 1;
+    }
+
+    size_t toCopy = std::min(bufferSize - 1, result.length());
+    ::memcpy(outputBuffer, result.data(), toCopy);
+    outputBuffer[toCopy] = '\0';
+
+    *status = 0;
+    return outputBuffer;
+#ifndef _WIN32
+  } else if (name.startswith("_Z")) {
+    // Try C++
+    size_t resultLen;
+    char *result = abi::__cxa_demangle(mangledName, nullptr, &resultLen, status);
+
+    if (result) {
+      size_t bufferSize;
+
+      if (outputBufferSize) {
+        bufferSize = *outputBufferSize;
+        *outputBufferSize = resultLen;
+      }
+
+      if (outputBuffer == nullptr) {
+        return result;
+      }
+
+      size_t toCopy = std::min(bufferSize - 1, resultLen - 1);
+      ::memcpy(outputBuffer, result, toCopy);
+      outputBuffer[toCopy] = '\0';
+
+      *status = 0;
+      return outputBuffer;
+    }
+#else
+    // On Windows, the mangling is different.
+    // ###TODO: Call __unDName()
+#endif
+  } else {
+    *status = -2;
+  }
+
+  return nullptr;
+}
+
 // N.B. THIS FUNCTION MUST BE SAFE TO USE FROM A CRASH HANDLER.  On Linux
 // and macOS, that means it must be async-signal-safe.  On Windows, there
 // isn't an equivalent notion but a similar restriction applies.
 SWIFT_RUNTIME_STDLIB_INTERNAL bool
+#ifdef __linux__
+_swift_spawnBacktracer(const ArgChar * const *argv, int memserver_fd)
+#else
 _swift_spawnBacktracer(const ArgChar * const *argv)
+#endif
 {
-#if TARGET_OS_OSX || TARGET_OS_MACCATALYST
+#if !SWIFT_BACKTRACE_ON_CRASH_SUPPORTED
+  return false;
+#elif TARGET_OS_OSX || TARGET_OS_MACCATALYST || defined(__linux__)
   pid_t child;
   const char *env[BACKTRACE_MAX_ENV_VARS + 1];
 
@@ -817,10 +967,16 @@ _swift_spawnBacktracer(const ArgChar * const *argv)
 
   // SUSv3 says argv and envp are "completely constant" and that the reason
   // posix_spawn() et al use char * const * is for compatibility.
+#ifdef __linux__
+  int ret = safe_spawn(&child, swiftBacktracePath, memserver_fd,
+                       const_cast<char * const *>(argv),
+                       const_cast<char * const *>(env));
+#else
   int ret = posix_spawn(&child, swiftBacktracePath,
                         &backtraceFileActions, &backtraceSpawnAttrs,
                         const_cast<char * const *>(argv),
                         const_cast<char * const *>(env));
+#endif
   if (ret < 0)
     return false;
 
@@ -835,10 +991,7 @@ _swift_spawnBacktracer(const ArgChar * const *argv)
 
   return false;
 
-  // ###TODO: Linux
   // ###TODO: Windows
-#else
-  return false;
 #endif
 }
 

stdlib/public/runtime/CMakeLists.txt

@@ -81,7 +81,8 @@ set(swift_runtime_sources
 
 set(swift_runtime_backtracing_sources
   Backtrace.cpp
-  CrashHandlerMacOS.cpp)
+  CrashHandlerMacOS.cpp
+  CrashHandlerLinux.cpp)
 
 # Acknowledge that the following sources are known.
 set(LLVM_OPTIONAL_SOURCES