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Fix warnings: ex_getln.c: init_history(): Double free: FP.

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Problem    : Double free @ 4249.
Diagnostic : False positive.
Rationale  : Codepath leading to error contains two consecutive
             iterations in which `if (--j < 0)` is true.
             That executes `free` two consecutive times with the same
             value (hislen - 1) for j, with leads to double free.
             Now, that can only happen with j == 0 && hislen == 1.
             And that would imply j == hisidx[type] too, which would
             take the following break.
             So, the error codepath cannot really happen, but the
             compiler cannot deduce the last implication.
Resolution : We have two possible solutions for this:
             1.- Comparing value of j before and after updating it,
                 and breaking out of iteration if equal.
                 That changes nothing in functionality, but teaches the
                 compiler his proposed error codepath is impossible.
             2.- Nullify pointer after freeing.
                 This way, the compiler still thinks his error codepath
                 is possible, but it's not an error anymore, as
                 free(NULL) is a no-op.
             We opt for solution 2, as solution 1 requires adding
             logic that adds nothing (and having to explain that clearly
             in aside comments) just for the purpose of silencing
             warning. On the other hand, solution 2 improves the code,
             adding something considered good practice in any case,
             and therefore doesn't require further explanation.
This commit is contained in:
Eliseo Martínez 2014-11-08 21:14:33 +01:00
parent ea1f883b19
commit d6472f459b
1 changed files with 3 additions and 1 deletions
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4
src/nvim/ex_getln.c
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@ -4245,8 +4245,10 @@ void init_history(void)
for (i = newlen - 1;; --i) {
if (i >= 0) /* copy newest entries */
temp[i] = history[type][j];
else /* remove older entries */
else { /* remove older entries */
free(history[type][j].hisstr);
history[type][j].hisstr = NULL;
}
if (--j < 0)
j = hislen - 1;
if (j == hisidx[type])