[PATCH 2/2] Windows libcpp: Make path-exists semantics more Posix-like

[Ray Donnelly <mingw dot android at gmail dot com>]

Windows does a short-circuit lookup of paths containing
../ which means that:

exists/doesnotexist/../file

is considered to exist, while on Posix it is considered
not to. The Posix semantics are relied upon when building
glibc so any paths containing "../" are checked component
wise.

libcpp/
	* files.c (open_file): Implement Posix existence
	semantics for paths containing '../'
---
 libcpp/ChangeLog |  5 ++++
 libcpp/files.c   | 86 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 91 insertions(+)

diff --git a/libcpp/ChangeLog b/libcpp/ChangeLog
index 3a63434..ae1b62a 100644
--- a/libcpp/ChangeLog
+++ b/libcpp/ChangeLog
@@ -1,3 +1,8 @@
+2014-04-14  Ray Donnelly  <mingw.android@gmail.com>
+
+	* files.c (open_file): Implement Posix existence
+	semantics for paths containing '../'
+
 2014-02-24  Walter Lee  <walt@tilera.com>
 
 	* configure.ac: Change "tilepro" triplet to "tilepro*".
diff --git a/libcpp/files.c b/libcpp/files.c
index 7e88778..a9326bf 100644
--- a/libcpp/files.c
+++ b/libcpp/files.c
@@ -30,6 +30,13 @@ along with this program; see the file COPYING3.  If not see
 #include "md5.h"
 #include <dirent.h>
 
+/* Needed for stat_st_mode_symlink below */
+#if defined(_WIN32)
+#  include <windows.h>
+#  define S_IFLNK 0xF000
+#  define S_ISLNK(m) (((m) & S_IFMT) == S_IFLNK)
+#endif
+
 /* Variable length record files on VMS will have a stat size that includes
    record control characters that won't be included in the read size.  */
 #ifdef VMS
@@ -198,6 +205,49 @@ static int pchf_save_compare (const void *e1, const void *e2);
 static int pchf_compare (const void *d_p, const void *e_p);
 static bool check_file_against_entries (cpp_reader *, _cpp_file *, bool);
 
+#if defined(_WIN32)
+
+static int stat_st_mode_symlink (char const* path, struct stat* buf)
+{
+  WIN32_FILE_ATTRIBUTE_DATA attr;
+  memset(buf, 0, sizeof(*buf));
+  int err = GetFileAttributesExA (path, GetFileExInfoStandard, &attr) ? 0 : 1;
+  if (!err)
+    {
+      WIN32_FIND_DATAA finddata;
+      HANDLE h = FindFirstFileA (path, &finddata);
+      if (h != INVALID_HANDLE_VALUE)
+        {
+          FindClose (h);
+          if ((finddata.dwFileAttributes & FILE_ATTRIBUTE_REPARSE_POINT) &&
+              (finddata.dwReserved0 == IO_REPARSE_TAG_SYMLINK))
+              buf->st_mode = S_IFLNK;
+          else if (finddata.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY)
+              buf->st_mode = S_IFDIR;
+          else if (finddata.dwFileAttributes & FILE_ATTRIBUTE_ARCHIVE)
+              buf->st_mode = S_IFDIR;
+          else
+              buf->st_mode = S_IFREG;
+          buf->st_mode |= S_IREAD;
+          if (!(finddata.dwFileAttributes & FILE_ATTRIBUTE_READONLY))
+              buf->st_mode |= S_IWRITE;
+        }
+      else
+        {
+          buf->st_mode = S_IFDIR;
+        }
+      return 0;
+    }
+  return -1;
+}
+
+#else
+
+#define stat_st_mode_symlink (_name, _buf) stat ((_name), (_buf))
+
+#endif
+
+
 /* Given a filename in FILE->PATH, with the empty string interpreted
    as <stdin>, open it.
 
@@ -227,6 +277,42 @@ open_file (_cpp_file *file)
     }
   else
     file->fd = open (file->path, O_RDONLY | O_NOCTTY | O_BINARY, 0666);
+#if defined(_WIN32) || defined(__CYGWIN__)
+  /* Windows and Posix differ in the face of paths of the form:
+     nonexistantdir/.. in that Posix will return ENOENT whereas
+     Windows won't care that we stepped into a non-existant dir
+     Only do these slow checks if "../" appears in file->path.
+     Cygwin also suffers from the same problem (but doesn't need
+     a new stat function):
+     http://cygwin.com/ml/cygwin/2013-05/msg00222.html
+  */
+  if (file->fd > 0)
+    {
+      char filepath[MAX_PATH];
+      strncpy (filepath, file->path, MAX_PATH);
+      filepath[MAX_PATH-1] = (char) 0;
+      char *dirsep = &filepath[0];
+      while ( (dirsep = strchr (dirsep, '\\')) != NULL)
+        *dirsep = '/';
+      if (strstr(filepath, "../"))
+	{
+	  dirsep = &filepath[0];
+	  /* Check each directory in the chain. */
+	  while ( (dirsep = strchr (dirsep, '/')) != NULL)
+	    {
+	      *dirsep = (char) 0;
+	      if (stat_st_mode_symlink (filepath, &file->st) == -1)
+	        {
+	          *dirsep = '/';
+	          close (file->fd);
+	          file->fd = -1;
+	          return false;
+	        }
+	      *dirsep = '/';
+	    }
+	}
+    }
+#endif
 
   if (file->fd != -1)
     {
-- 
1.9.2