* nanosleep truncated on 64 bit Linux by 292 billion years
[not found] ` <alpine.DEB.2.10.1408060017090.3323@nanos>
@ 2014-10-27 4:01 ` Pádraig Brady
2014-10-28 15:45 ` Thomas Gleixner
0 siblings, 1 reply; 2+ messages in thread
From: Pádraig Brady @ 2014-10-27 4:01 UTC (permalink / raw)
To: Thomas Gleixner, Linux Kernel Mailing List; +Cc: Paul Eggert, bug-gnulib
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I noticed that nanosleep() on 64 bit, "only" supports 292 years,
rather than the full potential 292 billion years with 64 bit time_t, due to:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/include/linux/time.h?id=refs/tags/v3.16#n87
Attached is a program from Paul Eggert that illustrates the bug.
Running this program on a buggy host outputs something like this:
Setting alarm for 1 second from now ...
Sleeping for 9223372036854775807.999999999 seconds...
After alarm sent off, remaining time is 9223357678.462306617 seconds;
i.e., nanosleep claimed that it slept for about 293079448610.606445 years.
Gnulib-using applications have a workaround for this bug, but a workaround
shouldn't be necessary. For what it's worth, the bug is fixed in Solaris 11 (x86-64),
though it's present in Solaris 10 (64-bit sparc).
thanks,
Pádraig.
[-- Attachment #2: nanosleep-bug.c --]
[-- Type: text/plain, Size: 1175 bytes --]
#include <time.h>
#include <errno.h>
#include <limits.h>
#include <stdio.h>
#include <signal.h>
#include <unistd.h>
static void
check_for_SIGALRM (int sig)
{
if (sig != SIGALRM)
_exit (1);
}
int
main (void)
{
static struct sigaction act;
struct timespec forever, remaining;
time_t time_t_max = (1ull << (sizeof time_t_max * CHAR_BIT - 1)) - 1;
act.sa_handler = check_for_SIGALRM;
sigemptyset (&act.sa_mask);
sigaction (SIGALRM, &act, NULL);
forever.tv_sec = time_t_max;
forever.tv_nsec = 999999999;
printf ("Setting alarm for 1 second from now ...\n");
alarm (1);
printf ("Sleeping for %lld.%09ld seconds...\n",
(long long) forever.tv_sec, forever.tv_nsec);
if (nanosleep (&forever, &remaining) == 0)
return 2;
if (errno != EINTR)
return 3;
if (remaining.tv_sec < time_t_max - 10)
{
printf ("After alarm sent off, remaining time is %lld.%09ld seconds;\n",
(long long) remaining.tv_sec, remaining.tv_nsec);
printf ("i.e., nanosleep claimed that it slept for about %f years.\n",
(forever.tv_sec - remaining.tv_sec) / (24 * 60 * 60 * 364.2425));
return 4;
}
printf ("ok\n");
return 0;
}
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