Lots of work on supporting swig-2


Sven Vermeulen Mon 20 August 2012

The SELinux setools package provides a few of the commands I used the most when working with SELinux: sesearch for looking through the policy and seinfo to get information on type/attribute/role/... from the currently loaded policy.

This package uses swig, the Simplified (sic) Wrapper and Interface Generator to provide libraries that can be loaded by Python and used as regular Python modules, based on the C code that setools uses. Or, in other words: you write C code, and swig transforms it into libraries that can be loaded by a dozen higher generation languages such as Python.

The change from swig-1 to swig-2 however broke the setools build. It seems that the swig interface code that setools uses doesn't work properly anymore with more recent swig versions. The last few days (yes, days) I have been trying to get setools to build again. The fixes that I put in were not extremely difficult, but very labour-intensive (beyond the point that I think I'm doing things wrong, but hey - this is my first time I'm working on swig stuff, and I'm glad I already got it to build again).

The first thing I had to do was fix constructor/destructor logic. It looks like swig-1 supported the C shorthand notation for structures whereas swig-2 sees the name of the structure as its class (note that I just got it to build, I still need to see if things still work):

  typedef struct apol_ip {...} apol_ip_t;
  %extend apol_ip_t {
-   apol_ip_t(const char * str) {
+   apol_ip(const char * str) {
-   ~apol_ip_t() {
+   ~apol_ip() {

Without this, I got "Illegal destructor" errors (not related to the illegal destructor fix made to swig itself) and "Method apol_ip_t requires a return type" (because it doesn't see them as constructors).

The second fix I had to introduce was to rename all functions that swig would generate which would then have the same name as the C-function. For instance, suppose a C function in the code has apol_vector_get_size then swig would, for the apol_vector class with method get_size in the swig interface, generate a function called apol_vector_get_size which of course collides with the already defined function, giving an error like "Conflicting types for apol_vector_get_size" followed by a "previous declaration was here:".

Swig supports the %rename method for this, so I had to do:

  typedef struct apol_vector {} apol_vector_t;
+ %rename(apol_vector_get_size) apol_vector_wrap_get_size;
+ %rename(apol_vector_get_capacity) apol_vector_wrap_get_capacity;
- size_t get_size() {
+ size_t wrap_get_size() {
- size_t get_capacity() {
+ size_t wrap_get_capacity() {

The patch that I had to add to finally get it to build again is 7019 lines (229 Kbyte). Too much manual labour. Now let's hope this really fixes things, and doesn't just masquerade the build failures but introduces runtime failures. Of course, if I think it works, I'll send it upstream so that, if it is indeed the right fix, other developers don't have to go through this...