https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85301
Bug ID: 85301
Summary: bitfield check causes maybe-uninitialized warning
Product: gcc
Version: 8.0.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: arnd at linaro dot org
Target Milestone: ---
A Linux kernel patch that changed a few flags from type 'int' to a single-bit
bitfield caused a false-positive warning. I reduced a test case to
struct tick_sched {
#ifdef USE_BITFIELD
unsigned int tick_stopped : 1;
unsigned int idle_active : 1;
#else
int tick_stopped;
int idle_active;
#endif
};
long ktime_get();
void __tick_nohz_idle_restart_tick(long);
struct tick_sched tick_nohz_idle_exit_ts;
void tick_nohz_idle_exit(void) {
long now;
if (tick_nohz_idle_exit_ts.idle_active ||
tick_nohz_idle_exit_ts.tick_stopped)
now = ktime_get();
if (tick_nohz_idle_exit_ts.tick_stopped)
__tick_nohz_idle_restart_tick(now);
}
$ gcc -c tick-sched.c -Wall -O2 -DUSE_BITFIELD
tick-sched.c: In function ‘tick_nohz_idle_exit’:
tick-sched.c:19:5: warning: ‘now’ may be used uninitialized in this function
[-Wmaybe-uninitialized]
__tick_nohz_idle_restart_tick(now);
$ gcc -c tick-sched.c -Wall -O2
# no warning
It's easy to work around the warning, e.g. by copying the flag into a temporary
variable, but it looks like this is something that gcc could handle better.
I looked through the list of false-positive Wmaybe-uninitialized bug reports,
but couldn't find one that looks related to this particular one.
