On Tue, May 28, 2024 at 12:37:23PM +0200, Mateusz Guzik wrote:
> I misplaced a closing ) in a patch using unlikely() and broke the
> comparison, see [1] for context.
>
> The fix was:
> - if (unlikely(abs(count + amount)) >= batch) {
> + if (unlikely(abs(count + amount) >= batch)) {
>
> Neither kernel build with W=1 nor C=1 (smatch) report the problem.
>
> Given that this compiles fine and for many cases with the bogus usage
> it also happens to produce the correct result, I have to suspect there
> are spots in the kernel with the problem.
>
> Either way, sounds like something smatch should be testing for.
>
> [1] https://lore.kernel.org/oe-lkp/pywb7wcml44gzgidn7mtwwr23mybbilakckchk4777wfibtruj@n4yiwwpvglf7/T/#t
Sure! I've created a check for that and I'll push it.
I think those bugs are rare, though. The last time we had one was maybe
in 2018.
regards,
dan carpenter
/*
* Copyright (C) 2018 Oracle.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
*/
#include "smatch.h"
#include "smatch_slist.h"
#include "smatch_extra.h"
static int my_id;
static void match_likely(const char *fn, struct expression *expr, void *unused)
{
struct expression *parent;
parent = expr_get_parent_expr(expr);
if (!parent || parent->type != EXPR_COMPARE)
return;
sm_warning("warn: check likely/unlikely parentheses");
}
void check_unlikely_parens(int id)
{
my_id = id;
add_function_hook("__builtin_expect", &match_likely, NULL);
}
