sync usertests

user/usertests.c

@@ -2591,6 +2591,16 @@ sbrklast(char *s)
     exit(1);
 }
 
+// does sbrk handle signed int32 wrap-around with
+// negative arguments?
+void
+sbrk8000(char *s)
+{
+  sbrk(0x80000004);
+  volatile char *top = sbrk(0);
+  *(top-1) = *(top-1) + 1;
+}
+
 // regression test. does write() with an invalid buffer pointer cause
 // a block to be allocated for a file that is then not freed when the
 // file is deleted? if the kernel has this bug, it will panic: balloc:
@@ -2832,6 +2842,7 @@ main(int argc, char *argv[])
     {sbrkfail, "sbrkfail"},
     {sbrkarg, "sbrkarg"},
     {sbrklast, "sbrklast"},
+    {sbrk8000, "sbrk8000"},
     {validatetest, "validatetest"},
     {stacktest, "stacktest"},
     {opentest, "opentest"},