Re: Memory protection between compilation units?

On Wed, 11 Jun 2025 14:32:39 GMT
scott@slp53.sl.home (Scott Lurndal) wrote:

=?UTF-8?Q?Josef_M=C3=B6llers?= <josef@invalid.invalid> writes:

On 11.06.25 15:32, Mateusz Viste wrote: 

This might not be a strictly C question, but it definitely
concerns all C programmers.
 
Earlier today, I fixed an out-of-bounds write bug. An obvious
issue:
 
   static int *socks[0xffff];
 
   void update_my_socks(int *sock, int val) {
     socks[val & 0xffff] = sock;
   }
 
While the presented issue is common knowledge for anyone familiar
with C, *locating* the bug was challenging. The program did not
crash at the moment of the out-of-bounds write but much later -
somewhere entirely different, in a different object file that
maintained a static pointer for tracking a position in a linked
list. To my surprise, the pointer was randomly reset to NULL about
once a week, causing a segfault. Tracing this back to an unrelated
out-of-bounds write elsewhere in the code was tedious, to say the
least. 

 
valgrind.
 

Probably too slow. If I were in Mateusz's situation, I would try
AddressSanitizer.
Never tried it myself, but it looks like better fit for this particular
relatively simple case of buffer overrun.