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time: switch to fences for siginfo_recvd

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This effectively reverts
6e824f3713 ("time: siginfo_recvd needs to be marked volatile")
because it was actually wrong.  Switch to C11 signal fence, which
provides a compiler barrier that will do the right thing.

Reported by:	kib
Reviewed by:	kib (slightly earlier version)
Differential Revision:	https://reviews.freebsd.org/D45574
This commit is contained in:
Kyle Evans 2025-04-20 22:19:17 -05:00
parent d7441aa9b0
commit df1b0f580d
1 changed files with 8 additions and 2 deletions
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10
usr.bin/time/time.c
View file

@ -40,6 +40,8 @@
#include <errno.h>
#include <locale.h>
#include <signal.h>
#include <stdatomic.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
@ -54,7 +56,7 @@ static void showtime(FILE *, struct timespec *, struct timespec *,
static void siginfo(int);
static void usage(void) __dead2;
static volatile sig_atomic_t siginfo_recvd;
static sig_atomic_t siginfo_recvd;
static char decimal_point;
static struct timespec before_ts;
static int hflag, pflag;
@ -125,7 +127,10 @@ main(int argc, char **argv)
(void)signal(SIGINFO, siginfo);
(void)siginterrupt(SIGINFO, 1);
while (wait4(pid, &status, 0, &ru) != pid) {
if (siginfo_recvd) {
bool do_siginfo = siginfo_recvd != 0;
atomic_signal_fence(memory_order_acquire);
if (do_siginfo) {
siginfo_recvd = 0;
if (clock_gettime(CLOCK_MONOTONIC, &after))
err(1, "clock_gettime");
@ -296,4 +301,5 @@ siginfo(int sig __unused)
{
siginfo_recvd = 1;
atomic_signal_fence(memory_order_release);
}