[dfsan] Fix a bug in strcasecmp() and strncasecmp(): Compare the lowercase versions of the characters when choosing a return value.

[skerner]

Summary

Resolves this bug:

https://bugs.llvm.org/show_bug.cgi?id=38369

[morehouse]

compiler-rt/test/dfsan/custom.cpp

217

IIUC, this test would still pass with the buggy code. I think the case we want is:

s1 = "ABCZ";
s2 = "abcy";
...
assert(rv > 0);

Since 'y' - 'Z' > 0 but 'y' - 'z' < 0.

264

Same as above.

[skerner]

Address review comments.

compiler-rt/test/dfsan/custom.cpp

217

Since 'y' - 'Z' > 0 but 'y' - 'z' < 0.

You are correct. It has been a few decades since I looked at an ASCII-code chart, and I was under the impression that lowercase chars had smaller values than uppercase.

Fixed.

[morehouse]

Looks like the diff lost the actual fix. Please add it back and I'll merge.

[skerner]

Address review comments.

[skerner]

Address review comments.

[skerner]

Diff issues...

[skerner]

All changes in one commit.

[skerner]

Looks like the diff lost the actual fix. Please add it back and I'll merge.

Done. PTAL.

[morehouse]

LGTM

compiler-rt/test/dfsan/custom.cpp

#endif
   rv = strcasecmp(str1, str3);
   assert(rv == 0);
 #ifdef STRICT_DATA_DEPENDENCIES
   ASSERT_ZERO_LABEL(rv);
 #else
   ASSERT_LABEL(rv, dfsan_union(i_label, j_label));
 #endif
 
-  char s1[] = "ABCz";
-  char s2[] = "abcY";
-  dfsan_set_label(i_label, &s1[3], 1);
-  dfsan_set_label(j_label, &s2[3], 1);
+  char s1[] = "AbZ";
+  char s2[] = "aBy";
+  dfsan_set_label(i_label, &s1[2], 1);
+  dfsan_set_label(j_label, &s2[2], 1);
 
   rv = strcasecmp(s1, s2);
-  assert(rv > 0); // 'z' > 'Y'
+  assert(rv > 0); // 'Z' > 'y'
 #ifdef STRICT_DATA_DEPENDENCIES
   ASSERT_ZERO_LABEL(rv);
 #else
   ASSERT_LABEL(rv, dfsan_union(i_label, j_label));
 #endif
 }
 
 void test_strncasecmp() {
   char str1[] = "Str1", str2[] = "str2";
   dfsan_set_label(i_label, &str1[3], 1);
   dfsan_set_label(j_label, &str2[3], 1);
 
   int rv = strncasecmp(str1, str2, sizeof(str1));
   assert(rv < 0);
 #ifdef STRICT_DATA_DEPENDENCIES
   ASSERT_ZERO_LABEL(rv);
 #else
   ASSERT_LABEL(rv, dfsan_union(i_label, j_label));
 #endif
 
   rv = strncasecmp(str1, str2, 3);
   assert(rv == 0);
   ASSERT_ZERO_LABEL(rv);
 
-  char s1[] = "ABCz";
-  char s2[] = "abcY";
-  dfsan_set_label(i_label, &s1[3], 1);
-  dfsan_set_label(j_label, &s2[3], 1);
+  char s1[] = "AbZ";
+  char s2[] = "aBy";
+  dfsan_set_label(i_label, &s1[2], 1);
+  dfsan_set_label(j_label, &s2[2], 1);
 
   rv = strncasecmp(s1, s2, 0);
   assert(rv == 0); // Compare zero chars.
   ASSERT_ZERO_LABEL(rv);
 
   rv = strncasecmp(s1, s2, 1);
-  assert(rv == 0); // 'a' == 'A'
+  assert(rv == 0); // 'A' == 'a'
   ASSERT_ZERO_LABEL(rv);
 
   rv = strncasecmp(s1, s2, 2);
   assert(rv == 0); // 'b' == 'B'
   ASSERT_ZERO_LABEL(rv);
 
   rv = strncasecmp(s1, s2, 3);
-  assert(rv == 0); // 'c' == 'C'
-  ASSERT_ZERO_LABEL(rv);
-
-  rv = strncasecmp(s1, s2, 4);
-  assert(rv > 0); // 'z' > 'Y'
+  assert(rv > 0); // 'Z' > 'y'
 #ifdef STRICT_DATA_DEPENDENCIES
   ASSERT_ZERO_LABEL(rv);
 #else
   ASSERT_LABEL(rv, dfsan_union(i_label, j_label));
 #endif
 }
 
 void test_strchr() {
   char str1[] = "str1";
   dfsan_set_label(i_label, &str1[3], 1);
 
   char *crv = strchr(str1, 'r');