[DFSan] Fix parameters to strtoull wrapper.

[morehouse]

Summary

base and nptr_label were swapped, which meant we were passing nptr's
shadow as the base to the operation. Usually, the shadow is 0, which
causes strtoull to guess the correct base from the string prefix (e.g.,
0x means base-16 and 0 means base-8), hiding this bug. Adjust the test
case to expose the bug.

[vitalybuka]

How did you find this?

[morehouse]

The DFMapper folks hit it during their DFSan experiments.

compiler-rt/lib/dfsan/dfsan_custom.cpp

unsigned long int __dfsw_strtoul(const char *nptr, char **endptr, int base,
   } else {
     *ret_label = 0;
   }
   return ret;
 }
 
 SANITIZER_INTERFACE_ATTRIBUTE
 long long unsigned int __dfsw_strtoull(const char *nptr, char **endptr,
-                                       dfsan_label nptr_label,
-                                       int base, dfsan_label endptr_label,
+                                       int base, dfsan_label nptr_label,
+                                       dfsan_label endptr_label,
                                        dfsan_label base_label,
                                        dfsan_label *ret_label) {
   char *tmp_endptr;
   long long unsigned int ret = strtoull(nptr, &tmp_endptr, base);
   if (endptr) {
     *endptr = tmp_endptr;
   }
   if (tmp_endptr > nptr) {

compiler-rt/test/dfsan/custom.cpp

void test_strtoll() {
   dfsan_set_label(j_label, buf + 2, 1);
   long long int ret = strtoll(buf, &endptr, 10);
   assert(ret == 1234578910);
   assert(endptr == buf + 10);
   ASSERT_LABEL(ret, i_j_label);
 }
 
 void test_strtoul() {
-  char buf[] = "0xffffffffffffaa";
+  char buf[] = "ffffffffffffaa";
   char *endptr = NULL;
   dfsan_set_label(i_label, buf + 1, 1);
   dfsan_set_label(j_label, buf + 2, 1);
   long unsigned int ret = strtol(buf, &endptr, 16);
   assert(ret == 72057594037927850);
-  assert(endptr == buf + 16);
+  assert(endptr == buf + 14);
   ASSERT_LABEL(ret, i_j_label);
 }
 
 void test_strtoull() {
-  char buf[] = "0xffffffffffffffaa";
+  char buf[] = "ffffffffffffffaa";
   char *endptr = NULL;
   dfsan_set_label(i_label, buf + 1, 1);
   dfsan_set_label(j_label, buf + 2, 1);
   long long unsigned int ret = strtoull(buf, &endptr, 16);
   assert(ret == 0xffffffffffffffaa);
-  assert(endptr == buf + 18);
+  assert(endptr == buf + 16);
   ASSERT_LABEL(ret, i_j_label);
 }
 
 void test_strtod() {
   char buf[] = "12345.76 foo";
   char *endptr = NULL;
   dfsan_set_label(i_label, buf + 1, 1);
   dfsan_set_label(j_label, buf + 6, 1);