Make Directory::Current() work with unenhanced POSIX getcwd

runtime/bin/directory_posix.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "bin/directory.h"
 
 #include <dirent.h>
 #include <errno.h>
 #include <sys/param.h>
 #include <sys/stat.h>
@@ skipping 358 matching lines @@
     ASSERT(errno == ELOOP ||
            errno == ENAMETOOLONG ||
            errno == ENOENT ||
            errno == ENOTDIR);
     return DOES_NOT_EXIST;
   }
 }
 
 
 char* Directory::Current() {
+#if defined(TARGET_OS_LINUX) || defined(TARGET_OS_MACOS)
+
+  // On targets that support it, let getcwd allocate the buffer
+  // dynamically. (Not part of POSIX, but implemented on many platforms.)
+
   return getcwd(NULL, 0);
+
+#else
+
+  // POSIX getcwd requires a pre-allocated buffer.
+
+  char buffer[PATH_MAX];
+  if (NULL == getcwd(buffer, PATH_MAX)) {
+    return NULL;
+  }
+
+  size_t length = strlen(buffer) + 1;
+  char* result = reinterpret_cast<char*>(malloc(length));
+  if (result == NULL) {
+    return NULL;
+  }
+
+  strncpy(result, buffer, length);
+  return result;
+
+#else
+#endif
 }
 
 
 bool Directory::Create(const char* dir_name) {
   // Create the directory with the permissions specified by the
   // process umask.
   return (TEMP_FAILURE_RETRY(mkdir(dir_name, 0777)) == 0);
 }
 
 
@@ skipping 33 matching lines @@
     return DeleteRecursively(dir_name);
   }
 }
 
 
 bool Directory::Rename(const char* path, const char* new_path) {
   ExistsResult exists = Exists(path);
   if (exists != EXISTS) return false;
   return (TEMP_FAILURE_RETRY(rename(path, new_path)) == 0);
 }