[analyzer] Provide a check name when MallocChecker enables CStringChecker

Fix an assertion failure caused by a missing CheckName. The malloc checker
enables "basic" support in the CStringChecker, which causes some CString
bounds checks to be enabled. In this case, make sure that we have a
valid CheckName for the BugType.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@323052 91177308-0d34-0410-b5e6-96231b3b80d8

lib/StaticAnalyzer/Checkers/CStringChecker.cpp

@@ -309,9 +309,19 @@ ProgramStateRef CStringChecker::CheckLocation(CheckerContext &C,
     if (!N)
       return nullptr;
 
+    CheckName Name;
+    // These checks are either enabled by the CString out-of-bounds checker
+    // explicitly or the "basic" CStringNullArg checker support that Malloc
+    // checker enables.
+    assert(Filter.CheckCStringOutOfBounds || Filter.CheckCStringNullArg);
+    if (Filter.CheckCStringOutOfBounds)
+      Name = Filter.CheckNameCStringOutOfBounds;
+    else
+      Name = Filter.CheckNameCStringNullArg;
+
     if (!BT_Bounds) {
       BT_Bounds.reset(new BuiltinBug(
-          Filter.CheckNameCStringOutOfBounds, "Out-of-bound array access",
+          Name, "Out-of-bound array access",
           "Byte string function accesses out-of-bound array element"));
     }
     BuiltinBug *BT = static_cast<BuiltinBug*>(BT_Bounds.get());

test/Analysis/Inputs/system-header-simulator.h

@@ -32,6 +32,7 @@ typedef __typeof(sizeof(int)) size_t;
 size_t strlen(const char *);
 
 char *strcpy(char *restrict, const char *restrict);
+char *strncpy(char *dst, const char *src, size_t n);
 void *memcpy(void *dst, const void *src, size_t n);
 
 typedef unsigned long __darwin_pthread_key_t;

test/Analysis/malloc.c

@@ -1777,6 +1777,15 @@ void freeFunctionPtr() {
   free((void *)fnptr); // expected-warning {{Argument to free() is a function pointer}}
 }
 
+// Enabling the malloc checker enables some of the buffer-checking portions
+// of the C-string checker.
+void cstringchecker_bounds_nocrash() {
+  char *p = malloc(2);
+  strncpy(p, "AAA", sizeof("AAA")); // expected-warning {{Size argument is greater than the length of the destination buffer}}
+
+  free(p);
+}
+
 // ----------------------------------------------------------------------------
 // False negatives.