V612. An unconditional 'break/continue/return/goto' within a loop.


The analyzer has detected an odd loop. One of the following operators is used in the loop body: break, continue, return, goto. These operators are executed always without any conditions.

Consider the following corresponding examples:

do {
  X();
  break;
} while (Foo();)

for (i = 0; i < 10; i++) {
  continue;
  Foo();
}

for (i = 0; i < 10; i++) {
  x = x + 1;
  return;
}

while (*p != 0) {
  x += *p++;
  goto endloop;
}
endloop:

The above shown examples of loops are artificial, of course, and of little interest to us. Now let's look at a code fragment found in one real application. We have abridged the function code to make it clearer.

int DvdRead(....)
{
  ....
  for (i=lsn; i<(lsn+sectors); i++){
    ....
//    switch (mode->datapattern){
//    case CdSecS2064:
      ((u32*)buf)[0] = i + 0x30000;
      memcpy_fast((u8*)buf+12, buff, 2048); 
      buf = (char*)buf + 2064; break;
//    default:
//      return 0;
//    }
  }
  ....
}

Some of the lines in the function are commented out. The trouble is that the programmer forgot to comment out the "break" operator.

When there were no comments, "break" was inside the "switch" body. Then "switch" was commented out and the "break" operator started to finish the loop earlier than it should. As a result, the loop body is executed only once.

This is the correct code:

buf = (char*)buf + 2064; // break;

Note that the V612 diagnostic rule is rather complicated: a lot of cases are accounted for, when using the break/continue/return/goto operator is quite correct. Let's examine a few cases when the V612 warning don't generated.

1) Presence of a condition.

while (*p != 0) {
  if (Foo(p))
    break;
}

2) Special methods used in macros usually:

do { Foo(x); return 1; } while(0);

3) Passing the 'continue' operator using 'goto':

for (i = 0; i < 10; i++) {
  if (x == 7) goto skipcontinue;
  continue;
skipcontinue: Foo(x);
}

There are other methods possible which are used in practice and are unknown to us. If you have noticed that the analyzer generates false V612 warnings, please write to us and send us the corresponding samples. We will study them and try to make exceptions to these cases.



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