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
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