Add gnulib modules to replace missing libc functionality

This enables us to build a fully featured elfutils package on systems
with reduced C libraries, such as windows. All the modules are built
into libgnu.a, which is then linked into all binaries if
--enable-gnulib is given on the configure line.

Change-Id: I743fd22172bc85d9f10dcc3dad8eb921f462b554
Reviewed-by: Christian Kandeler <[email protected]>

1 files changed, 74 insertions, 0 deletions

diff --git a/libgnu/readlink.c b/libgnu/readlink.c
new file mode 100644
index 00000000..bf0cedc5
--- /dev/null
+++ b/libgnu/readlink.c
@@ -0,0 +1,74 @@
+/* Stub for readlink().
+   Copyright (C) 2003-2007, 2009-2017 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include <unistd.h>
+
+#include <errno.h>
+#include <string.h>
+#include <sys/stat.h>
+
+#if !HAVE_READLINK
+
+/* readlink() substitute for systems that don't have a readlink() function,
+   such as DJGPP 2.03 and mingw32.  */
+
+ssize_t
+readlink (const char *name, char *buf _GL_UNUSED,
+          size_t bufsize _GL_UNUSED)
+{
+  struct stat statbuf;
+
+  /* In general we should use lstat() here, not stat().  But on platforms
+     without symbolic links, lstat() - if it exists - would be equivalent to
+     stat(), therefore we can use stat().  This saves us a configure check.  */
+  if (stat (name, &statbuf) >= 0)
+    errno = EINVAL;
+  return -1;
+}
+
+#else /* HAVE_READLINK */
+
+# undef readlink
+
+/* readlink() wrapper that uses correct types, for systems like cygwin
+   1.5.x where readlink returns int, and which rejects trailing slash,
+   for Solaris 9.  */
+
+ssize_t
+rpl_readlink (const char *name, char *buf, size_t bufsize)
+{
+# if READLINK_TRAILING_SLASH_BUG
+  size_t len = strlen (name);
+  if (len && name[len - 1] == '/')
+    {
+      /* Even if name without the slash is a symlink to a directory,
+         both lstat() and stat() must resolve the trailing slash to
+         the directory rather than the symlink.  We can therefore
+         safely use stat() to distinguish between EINVAL and
+         ENOTDIR/ENOENT, avoiding extra overhead of rpl_lstat().  */
+      struct stat st;
+      if (stat (name, &st) == 0)
+        errno = EINVAL;
+      return -1;
+    }
+# endif /* READLINK_TRAILING_SLASH_BUG */
+  return readlink (name, buf, bufsize);
+}
+
+#endif /* HAVE_READLINK */