C++: Ignore free calls that are macro defined or #if/#ifdef guarded

Author: jketema

cpp/ql/src/experimental/Best Practices/GuardedFree.ql

@@ -18,6 +18,17 @@ class FreeCall extends FunctionCall {
   FreeCall() { this.getTarget().hasGlobalName("free") }
 }
 
+predicate isAffectedByMacro(FreeCall fc, BasicBlock bb) {
+  fc.isInMacroExpansion()
+  or
+  exists(PreprocessorBranch ppb, Location bbLoc, Location ppbLoc |
+    bbLoc = bb.(Stmt).getLocation() and ppbLoc = ppb.getLocation()
+  |
+    bbLoc.getStartLine() < ppbLoc.getStartLine() and
+    ppbLoc.getEndLine() < bbLoc.getEndLine()
+  )
+}
+
 from GuardCondition gc, FreeCall fc, Variable v, BasicBlock bb
 where
   gc.ensuresEq(v.getAnAccess(), 0, bb, false) and
@@ -28,5 +39,6 @@ where
     or
     strictcount(bb.(BlockStmt).getAStmt()) = 1
   ) and
-  strictcount(BasicBlock bb2 | gc.ensuresEq(_, 0, bb2, _) | bb2) = 1
+  strictcount(BasicBlock bb2 | gc.ensuresEq(_, 0, bb2, _) | bb2) = 1 and
+  not isAffectedByMacro(fc, bb)
 select gc, "unnecessary NULL check before call to $@", fc, "free"

cpp/ql/test/experimental/query-tests/Best Practices/GuardedFree/GuardedFree.expected

@@ -3,8 +3,5 @@
 | test.cpp:31:7:31:24 | ... \|\| ... | unnecessary NULL check before call to $@ | test.cpp:35:3:35:6 | call to free | free |
 | test.cpp:42:7:42:7 | x | unnecessary NULL check before call to $@ | test.cpp:43:5:43:8 | call to free | free |
 | test.cpp:49:7:49:7 | x | unnecessary NULL check before call to $@ | test.cpp:50:5:50:8 | call to free | free |
-| test.cpp:75:7:75:7 | x | unnecessary NULL check before call to $@ | test.cpp:76:5:76:14 | call to free | free |
-| test.cpp:81:7:81:7 | x | unnecessary NULL check before call to $@ | test.cpp:85:5:85:8 | call to free | free |
-| test.cpp:94:12:94:12 | x | unnecessary NULL check before call to $@ | test.cpp:94:3:94:13 | call to free | free |
 | test.cpp:106:7:106:18 | ... != ... | unnecessary NULL check before call to $@ | test.cpp:107:5:107:8 | call to free | free |
 | test.cpp:113:7:113:18 | ... != ... | unnecessary NULL check before call to $@ | test.cpp:114:17:114:20 | call to free | free |

cpp/ql/test/experimental/query-tests/Best Practices/GuardedFree/test.cpp

@@ -72,13 +72,13 @@ bool test8(char *x) {
 #endif
 
 void test9(char *x) {
-  if (x) { // GOOD [FALSE POSITIVE]: macro may make free behave unexpectedly when compiled differently
+  if (x) { // GOOD: macro may make free behave unexpectedly when compiled differently
     my_free(x);
   }
 }
 
 void test10(char *x) {
-  if (x) { // GOOD [FALSE POSITIVE]: #ifdef may make free behave unexpectedly when compiled differently
+  if (x) { // GOOD: #ifdef may make free behave unexpectedly when compiled differently
 #ifdef FOO
     free(x - 1);
 #else
@@ -91,7 +91,7 @@ void test10(char *x) {
   if (x) free(x);
 
 void test11(char *x) {
-  TRY_FREE(x) // BAD
+  TRY_FREE(x) // BAD [NOT DETECTED]
 }
 
 bool test12(char *x) {