semtimedop: add time64 syscall support, decouple 32-bit time_t

time64 syscall is used only if it's the only one defined for the arch,
or if the requested timeout does not fit in 32 bits. on current 32-bit
archs where time_t is a 32-bit type, this makes it statically
unreachable.

on 64-bit archs, there is no change to the code after preprocessing.
on current 32-bit archs, the time is passed via an intermediate copy
to remove the assumption that time_t is a 32-bit type.

to avoid duplicating SYS_ipc/SYS_semtimedop choice logic, the code for
32-bit archs "falls through" after updating the timeout argument ts to
point to a [compound literal] array of longs. in preparation for
"time64-only" 32-bit archs, an extra case is added for neither SYS_ipc
nor the non-time64 SYS_semtimedop existing; the ENOSYS failure path
here should never be reachable, and is added just in case a compiler
can't see that it's not reachable, to avoid spurious static analysis
complaints.

src/ipc/semtimedop.c

@@ -1,13 +1,35 @@
 #define _GNU_SOURCE
 #include <sys/sem.h>
+#include <errno.h>
 #include "syscall.h"
 #include "ipc.h"
 
+#define IS32BIT(x) !((x)+0x80000000ULL>>32)
+#define CLAMP(x) (int)(IS32BIT(x) ? (x) : 0x7fffffffU+((0ULL+(x))>>63))
+
+#if !defined(SYS_semtimedop) && !defined(SYS_ipc)
+#define NO_TIME32 1
+#else
+#define NO_TIME32 0
+#endif
+
 int semtimedop(int id, struct sembuf *buf, size_t n, const struct timespec *ts)
 {
-#ifndef SYS_ipc
+#ifdef SYS_semtimedop_time64
+	time_t s = ts ? ts->tv_sec : 0;
+	long ns = ts ? ts->tv_nsec : 0;
+	int r = -ENOSYS;
+	if (NO_TIME32 || !IS32BIT(s))
+		r = __syscall(SYS_semtimedop_time64, id, buf, n,
+			ts ? ((long long[]){s, ns}) : 0);
+	if (NO_TIME32 || r!=-ENOSYS) return __syscall_ret(r);
+	ts = ts ? (void *)(long[]){CLAMP(s), ns} : 0;
+#endif
+#if defined(SYS_ipc)
+	return syscall(SYS_ipc, IPCOP_semtimedop, id, n, 0, buf, ts);
+#elif defined(SYS_semtimedop)
 	return syscall(SYS_semtimedop, id, buf, n, ts);
 #else
-	return syscall(SYS_ipc, IPCOP_semtimedop, id, n, 0, buf, ts);
+	return __syscall_ret(-ENOSYS);
 #endif
 }