tree 68f9c16df4248cc544855bed4644c0065a2e7c64
parent e3283ec3eb8d74423694ff5d54838ca6205f6991
author Jacob Erlbeck <jerlbeck@sysmocom.de> 1409565311 +0200
committer Jacob Erlbeck <jerlbeck@sysmocom.de> 1409644398 +0200

gbproxy: Remove nonnull attributes

The compiler also uses this attribute for code elimination. If the
nonnull attribute has been given erroneously for an parameter, that
is later been checked against NULL, this check is removed silently
by the gcc if optimization is enabled. This can lead to hard-to-find
segmentation violation faults.

To be on the safe side, this patch removes all uses of the nonnull
attribute in openbsc.

Compiler:
  - gcc 4.8.2 (Ubuntu 4.8.2-19ubuntu1): no warning, segfault
  - clang 3.4 (3.4-1ubuntu3): no warning, no segfault, asm ok

Example:
  /* foo.c */
  int f(int* p) __attribute((nonnull));
  int f(int *p) {
      if (!p)
          return 0;

      return *p;
  }

  /* main.c */
  int f(int* p) __attribute((nonnull));
  int g () {
      return f(arg);
  }

  int main() {
      return g(NULL);
  }

When these files are compiled into an executable, no warnungs are
issued but it will fail with a segfault when -O2 is used (unless LTO
is active).

Compiler output (gcc -O2):
  int f(int *p) {
    0:  8b 44 24 04             mov    0x4(%esp),%eax
    4:  8b 00                   mov    (%eax),%eax
    6:  c3                      ret
  }

Sponsored-by: On-Waves ehf