Don't conflate the error variable in nxt_kqueue_poll().

In nxt_kqueue_poll() error is declared as a nxt_bool_t aka unsigned int
(on x86-64 anyway).

It is used both as a boolean and as the return storage for a bitwise AND
operation.

This causes the following issue after we have changed nxt_bool_t to be a
uint8_t (which will happen in a subsequent commit)

gcc12 -c -pipe -fPIC -fvisibility=hidden -O -W -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wmissing-prototypes -Werror -g -O2 -I src -I build     -I/usr/local/include  -o build/src/nxt_kqueue_engine.o  -MMD -MF build/src/nxt_kqueue_engine.dep -MT build/src/nxt_kqueue_engine.o  src/nxt_kqueue_engine.c
src/nxt_kqueue_engine.c: In function 'nxt_kqueue_poll':
src/nxt_kqueue_engine.c:728:17: error: overflow in conversion from 'int' to 'nxt_bool_t' {aka 'unsigned char'} changes value from '(int)kev->flags & 16384' to '0' [-Werror=overflow]
  728 |         error = (kev->flags & EV_ERROR);
      |                 ^
cc1: all warnings being treated as errors

EV_ERROR has the value 16384, after the AND operation error holds 16384,
however this overflows and wraps around (64 times) exactly to 0.

Rather than conflating the use of error, keep error as a boolean (it is
used further down the function) but do the AND operation inside the
if ().

Reviewed-by: Alejandro Colomar <alx@nginx.com>
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/src/nxt_kqueue_engine.c b/src/nxt_kqueue_engine.c
index ecc3251e..a7a5a29e 100644
--- a/src/nxt_kqueue_engine.c
+++ b/src/nxt_kqueue_engine.c
@@ -716,6 +716,8 @@ nxt_kqueue_poll(nxt_event_engine_t *engine, nxt_msec_t timeout)
 
     for (i = 0; i < nevents; i++) {
 
+        error = 0;
+
         kev = &engine->u.kqueue.events[i];
 
         nxt_debug(&engine->task,
@@ -725,12 +727,11 @@ nxt_kqueue_poll(nxt_event_engine_t *engine, nxt_msec_t timeout)
                   kev->ident, kev->filter, kev->flags, kev->fflags,
                   kev->data, kev->udata);
 
-        error = (kev->flags & EV_ERROR);
-
-        if (nxt_slow_path(error)) {
+        if (nxt_slow_path(kev->flags & EV_ERROR)) {
             nxt_alert(&engine->task,
                       "kevent(%d) error %E on ident:%d filter:%d",
                       engine->u.kqueue.fd, kev->data, kev->ident, kev->filter);
+            error = 1;
         }
 
         task = &engine->task;