kdiff3: FTBFS on hurd-i386 (for review)

[Svante Signell <svante.signell@gmail.com>]

Source: kdiff3
Version: 0.9.98-1
Severity: important
Tags: patch
User: debian-hurd@lists.debian.org
Usertags: hurd

Hi, kdiff3 does not build on GNU/Hurd since PATH_MAX is not defined. It
did build before, and the latest Hurd version is 0.9.97-3. Instead of
using realpath() with a fixed size buffer length this patch use the
lstat() call to find out the necessary string length, dynamically
allocate it, and free it when no longer needed.

Thanks!

Questions:

- This patch has a lot of C-code in it in the C++ file.

- The patch contains fprintf statements, should cout/no printing be used
instead?

- No complaints from the compiler, even if <stdio.h> is not included,
etc?

- Return values of the function are not used in the original code, the
return value is void. Is that needed here? Better ways to exit the
function on error?

--- a/src-QT4/fileaccess.cpp.orig	2014-07-03 13:37:37.000000000 +0200
+++ b/src-QT4/fileaccess.cpp		2014-09-24 14:52:37.000000000 +0200
@@ -235,8 +235,32 @@
          d()->m_linkTarget = fi.readLink();
 #else
          // Unfortunately Qt4 readLink always returns an absolute path, even if the link is relative
-         char s[PATH_MAX+1];
-         int len = readlink(QFile::encodeName(fi.absoluteFilePath()).constData(), s, PATH_MAX);
+	 struct stat sb;
+	 char *s;
+	 ssize_t len;
+	 const char *path = QFile::encodeName(fi.absoluteFilePath()).constData();
+
+	 if (lstat(path, &sb) == -1)
+	   exit(EXIT_FAILURE);
+
+	 s = (char*)malloc(sb.st_size + 1);
+	 if (s == NULL) {
+	   fprintf(stderr, "insufficient memory\n");
+	   exit(EXIT_FAILURE);
+	 }
+
+	 len = readlink(path, s, sb.st_size + 1);
+	 if (len == -1) {
+	   perror("readlink");
+	   exit(EXIT_FAILURE);
+	 }
+
+	 if (len > sb.st_size) {
+	   fprintf(stderr, "symlink increased in size "
+		   "between lstat() and readlink()\n");
+	   exit(EXIT_FAILURE);
+	 }
+
          if ( len>0 )
          {
             s[len] = '\0';
@@ -246,6 +270,7 @@
          {
             d()->m_linkTarget = fi.readLink();
          }
+	 free(s);
 #endif
       }
       d()->m_bLocal = true;