Redefine ADJFREQ_MIN to avoid undefined behaviour (when not using -fwrapv)

Change the definition of ADJFREQ_MIN so that it does not shift
a negative value. Such shifting is undefined in standard C.

This came up when cross-compiling the kernel using ports clang.
The shifting becomes defined when compiling with option -fwrapv.
Base clang enables this option by default.

OK naddy@ cheloha@

diff --git a/sys/kern/kern_time.c b/sys/kern/kern_time.c
index aa380e0..37771cc 100644 (file)
--- a/sys/kern/kern_time.c
+++ b/sys/kern/kern_time.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: kern_time.c,v 1.151 2020/12/23 20:45:02 cheloha Exp $ */
+/*     $OpenBSD: kern_time.c,v 1.152 2021/05/31 12:45:33 visa Exp $    */
 /*     $NetBSD: kern_time.c,v 1.20 1996/02/18 11:57:06 fvdl Exp $      */
 
 /*
@@ -396,7 +396,7 @@ sys_settimeofday(struct proc *p, void *v, register_t *retval)
 }
 
 #define ADJFREQ_MAX (500000000LL << 32)
-#define ADJFREQ_MIN (-500000000LL << 32)
+#define ADJFREQ_MIN (-ADJFREQ_MAX)
 
 int
 sys_adjfreq(struct proc *p, void *v, register_t *retval)