Re: gcc 4.1 bug miscompiles pointer range checks, may place you at risk
* Felix von Leitner:
> static inline int range_ptrinbuf(const void* buf,unsigned long len,const
> void* ptr) {
> register const char* c=(const char*)buf; /* no pointer arithmetic on
> void* */
> return (c && c+len>c && (const char*)ptr-c<len);
> }
It seems that the problem is that
c + len > c
is equivalent to
len != 0.
Either c + len is within the same object c points to, and it's value
is larger than c (provided that len is not zero), or c + len is
undefined (because it's not the same object). In the latter case, the
outcome is not specified by the C standard (or the GCC documentation),
so it's permissible to choose len != 0 as the value, too.
I wouldn't rule out a compiler bug in this area, but the test case is
invalid.