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<h1>Alpha Checkers</h1>
Experimental checkers in addition to the <a href = "available_checks.html">
Default Checkers</a>. These are checkers with known issues or limitations that
keep them from being on by default. They are likely to have false positives.
Bug reports are welcome but will likely not be investigated for some time.
Patches welcome!
<ul>
<li><a href="#core_alpha_checkers">Core Alpha Checkers</a></li>
<li><a href="#cplusplus_alpha_checkers">C++ Alpha Checkers</a></li>
<li><a href="#deadcode_alpha_checkers">Dead Code Alpha Checkers</a></li>
<li><a href="#osx_alpha_checkers">OS X Alpha Checkers</a></li>
<li><a href="#security_alpha_checkers">Security Alpha Checkers</a></li>
<li><a href="#unix_alpha_checkers">Unix Alpha Checkers</a></li>
</ul>

<!------------------------------ core alpha ----------------------------------->
<h3 id="core_alpha_checkers">Core Alpha Checkers</h3>
<table class="checkers">
<colgroup><col class="namedescr"><col class="example"></colgroup>
<thead><tr><td>Name, Description</td><td>Example</td></tr></thead>

<tbody>
<tr><td><div class="namedescr expandable"><span class="name">
alpha.core.BoolAssignment</span><span class="lang">
(ObjC)</span><div class="descr">
Warn about assigning non-{0,1} values to boolean variables.</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
void test() {
  BOOL b = -1; // warn
}
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.core.CastSize</span><span class="lang">
(C)</span><div class="descr">
Check when casting a malloc'ed type T, whether the size is a multiple of the
size of T (Works only with <span class="name">unix.Malloc</span>
or <span class="name">alpha.unix.MallocWithAnnotations</span>
checks enabled).</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
void test() {
  int *x = (int *)malloc(11); // warn
}
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.core.CastToStruct</span><span class="lang">
(C, C++)</span><div class="descr">
Check for cast from non-struct pointer to struct pointer.</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
// C
struct s {};

void test(int *p) {
  struct s *ps = (struct s *) p; // warn
}
</pre></div><div class="separator"></div>
<div class="example"><pre>
// C++
class c {};

void test(int *p) {
  c *pc = (c *) p; // warn
}
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.core.FixedAddr</span><span class="lang">
(C)</span><div class="descr">
Check for assignment of a fixed address to a pointer.</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
void test() {
  int *p;
  p = (int *) 0x10000; // warn
}
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.core.IdenticalExpr</span><span class="lang">
(C, C++)</span><div class="descr">
Warn about suspicious uses of identical expressions.</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
// C
void test() {
  int a = 5;
  int b = a | 4 | a; // warn: identical expr on both sides
}
</pre></div><div class="separator"></div>
<div class="example"><pre>
// C++
bool f(void);

void test(bool b) {
  int i = 10;
  if (f()) { // warn: true and false branches are identical
    do {
      i--;
    } while (f());
  } else {
    do {
      i--;
    } while (f());
  }
}
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.core.PointerArithm</span><span class="lang">
(C)</span><div class="descr">
Check for pointer arithmetic on locations other than array
elements.</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
void test() {
  int x;
  int *p;
  p = &amp;x + 1; // warn
}
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.core.PointerSub</span><span class="lang">
(C)</span><div class="descr">
Check for pointer subtractions on two pointers pointing to different memory
chunks.</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
void test() {
  int x, y;
  int d = &amp;y - &amp;x; // warn
}
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.core.SizeofPtr</span><span class="lang">
(C)</span><div class="descr">
Warn about unintended use of <code>sizeof()</code> on pointer
expressions.</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
struct s {};

int test(struct s *p) {
  return sizeof(p);
    // warn: sizeof(ptr) can produce an unexpected result
}
</pre></div></div></td></tr>

</tbody></table>

<!--------------------------- cplusplus alpha --------------------------------->
<h3 id="cplusplus_alpha_checkers">C++ Alpha Checkers</h3>
<table class="checkers">
<colgroup><col class="namedescr"><col class="example"></colgroup>
<thead><tr><td>Name, Description</td><td>Example</td></tr></thead>

<tbody>
<tr><td><div class="namedescr expandable"><span class="name">
alpha.cplusplus.NewDeleteLeaks</span><span class="lang">
(C++)</span><div class="descr">
Check for memory leaks. Traces memory managed by <code>new</code>/<code>
delete</code>.</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
void test() {
  int *p = new int;
} // warn
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.cplusplus.VirtualCall</span><span class="lang">
(C++)</span><div class="descr">
Check virtual member function calls during construction or
destruction.</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
class A {
public:
  A() {
    f(); // warn
  }
  virtual void f();
};
</pre></div><div class="separator"></div>
<div class="example"><pre>
class A {
public:
  ~A() {
    this-&gt;f(); // warn
  }
  virtual void f();
};
</pre></div></div></td></tr>

</tbody></table>

<!--------------------------- dead code alpha --------------------------------->
<h3 id="deadcode_alpha_checkers">Dead Code Alpha Checkers</h3>
<table class="checkers">
<colgroup><col class="namedescr"><col class="example"></colgroup>
<thead><tr><td>Name, Description</td><td>Example</td></tr></thead>

<tbody>
<tr><td><div class="namedescr expandable"><span class="name">
alpha.deadcode.UnreachableCode</span><span class="lang">
(C, C++, ObjC)</span><div class="descr">
Check unreachable code.</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
// C
int test() {
  int x = 1;
  while(x);
  return x; // warn
}
</pre></div><div class="separator"></div>
<div class="example"><pre>
// C++
void test() {
  int a = 2;

  while (a > 1)
    a--;

  if (a > 1)
    a++; // warn
}
</pre></div><div class="separator"></div>
<div class="example"><pre>
// Objective-C
void test(id x) {
  return;
  [x retain]; // warn
}
</pre></div></div></td></tr>
</tbody></table>

<!---------------------------- OS X alpha -------------------------------------->
<h3 id="osx_alpha_checkers">OS X Alpha Checkers</h3>
<table class="checkers">
<colgroup><col class="namedescr"><col class="example"></colgroup>
<thead><tr><td>Name, Description</td><td>Example</td></tr></thead>

<tbody>
<tr><td><div class="namedescr expandable"><span class="name">
alpha.osx.cocoa.Dealloc</span><span class="lang">
(ObjC)</span><div class="descr">
Warn about Objective-C classes that lack a correct implementation
of <code>-dealloc</code>.
</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
@interface MyObject : NSObject {
  id _myproperty;
}
@end

@implementation MyObject // warn: lacks 'dealloc'
@end
</pre></div><div class="separator"></div>
<div class="example"><pre>
@interface MyObject : NSObject {}
@property(assign) id myproperty;
@end

@implementation MyObject // warn: does not send 'dealloc' to super
- (void)dealloc {
  self.myproperty = 0;
}
@end
</pre></div><div class="separator"></div>
<div class="example"><pre>
@interface MyObject : NSObject {
  id _myproperty;
}
@property(retain) id myproperty;
@end

@implementation MyObject
@synthesize myproperty = _myproperty;
  // warn: var was retained but wasn't released
- (void)dealloc {
  [super dealloc];
}
@end
</pre></div><div class="separator"></div>
<div class="example"><pre>
@interface MyObject : NSObject {
  id _myproperty;
}
@property(assign) id myproperty;
@end

@implementation MyObject
@synthesize myproperty = _myproperty;
  // warn: var wasn't retained but was released
- (void)dealloc {
  [_myproperty release];
  [super dealloc];
}
@end
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.osx.cocoa.DirectIvarAssignment</span><span class="lang">
(ObjC)</span><div class="descr">
Check that Objective C properties follow the following rule: the property
should be set with the setter, not though a direct assignment.</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
@interface MyClass : NSObject {}
@property (readonly) id A;
- (void) foo;
@end

@implementation MyClass
- (void) foo {
  _A = 0; // warn
}
@end
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.osx.cocoa.DirectIvarAssignmentForAnnotatedFunctions</span><span class="lang">
(ObjC)</span><div class="descr">
Check for direct assignments to instance variables in the methods annotated
with <code>objc_no_direct_instance_variable_assignment</code>.</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
@interface MyClass : NSObject {}
@property (readonly) id A;
- (void) fAnnotated __attribute__((
    annotate("objc_no_direct_instance_variable_assignment")));
- (void) fNotAnnotated;
@end

@implementation MyClass
- (void) fAnnotated {
  _A = 0; // warn
}
- (void) fNotAnnotated {
  _A = 0; // no warn
}
@end
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.osx.cocoa.InstanceVariableInvalidation</span><span class="lang">
(ObjC)</span><div class="descr">
Check that the invalidatable instance variables are invalidated in the methods
annotated with <code>objc_instance_variable_invalidator</code>.</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
@protocol Invalidation &lt;NSObject&gt;
- (void) invalidate
  __attribute__((annotate("objc_instance_variable_invalidator")));
@end

@interface InvalidationImpObj : NSObject &lt;Invalidation&gt;
@end

@interface SubclassInvalidationImpObj : InvalidationImpObj {
  InvalidationImpObj *var;
}
- (void)invalidate;
@end

@implementation SubclassInvalidationImpObj
- (void) invalidate {}
@end
// warn: var needs to be invalidated or set to nil
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.osx.cocoa.MissingInvalidationMethod</span><span class="lang">
(ObjC)</span><div class="descr">
Check that the invalidation methods are present in classes that contain
invalidatable instance variables.</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
@protocol Invalidation &lt;NSObject&gt;
- (void)invalidate
  __attribute__((annotate("objc_instance_variable_invalidator")));
@end

@interface NeedInvalidation : NSObject &lt;Invalidation&gt;
@end

@interface MissingInvalidationMethodDecl : NSObject {
  NeedInvalidation *Var; // warn
}
@end

@implementation MissingInvalidationMethodDecl
@end
</pre></div></div></td></tr>

</tbody></table>

<!------------------------- security alpha ------------------------------------>
<h3 id="security_alpha_checkers">Security Alpha Checkers</h3>
<table class="checkers">
<colgroup><col class="namedescr"><col class="example"></colgroup>
<thead><tr><td>Name, Description</td><td>Example</td></tr></thead>

<tbody>
<tr><td><div class="namedescr expandable"><span class="name">
alpha.security.ArrayBound</span><span class="lang">
(C)</span><div class="descr">
Warn about buffer overflows (older checker).</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
void test() {
  char *s = "";
  char c = s[1]; // warn
}
</pre></div><div class="separator"></div>
<div class="example"><pre>
struct seven_words {
  int c[7];
};

void test() {
  struct seven_words a, *p;
  p = &a;
  p[0] = a;
  p[1] = a;
  p[2] = a; // warn
}
</pre></div><div class="separator"></div>
<div class="example"><pre>
// note: requires unix.Malloc or
// alpha.unix.MallocWithAnnotations checks enabled.
void test() {
  int *p = malloc(12);
  p[3] = 4; // warn
}
</pre></div><div class="separator"></div>
<div class="example"><pre>
void test() {
  char a[2];
  int *b = (int*)a;
  b[1] = 3; // warn
}
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.security.ArrayBoundV2</span><span class="lang">
(C)</span><div class="descr">
Warn about buffer overflows (newer checker).</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
void test() {
  char *s = "";
  char c = s[1]; // warn
}
</pre></div><div class="separator"></div>
<div class="example"><pre>
void test() {
  int buf[100];
  int *p = buf;
  p = p + 99;
  p[1] = 1; // warn
}
</pre></div><div class="separator"></div>
<div class="example"><pre>
// note: compiler has internal check for this.
// Use -Wno-array-bounds to suppress compiler warning.
void test() {
  int buf[100][100];
  buf[0][-1] = 1; // warn
}
</pre></div><div class="separator"></div>
<div class="example"><pre>
// note: requires alpha.security.taint check turned on.
void test() {
  char s[] = "abc";
  int x = getchar();
  char c = s[x]; // warn: index is tainted
}
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.security.MallocOverflow</span><span class="lang">
(C)</span><div class="descr">
Check for overflows in the arguments to <code>malloc()</code>.</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
void test(int n) {
  void *p = malloc(n * sizeof(int)); // warn
}
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.security.ReturnPtrRange</span><span class="lang">
(C)</span><div class="descr">
Check for an out-of-bound pointer being returned to callers.</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
static int A[10];

int *test() {
  int *p = A + 10;
  return p; // warn
}
</pre></div><div class="separator"></div>
<div class="example"><pre>
int test(void) {
  int x;
  return x; // warn: undefined or garbage returned
}
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.security.taint.TaintPropagation</span><span class="lang">
(C)</span><div class="descr">
Generate taint information used by other checkers.</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
void test() {
  char x = getchar(); // 'x' marked as tainted
  system(&x); // warn: untrusted data is passed to a system call
}
</pre></div><div class="separator"></div>
<div class="example"><pre>
// note: compiler internally checks if the second param to
// sprintf is a string literal or not.
// Use -Wno-format-security to suppress compiler warning.
void test() {
  char s[10], buf[10];
  fscanf(stdin, "%s", s); // 's' marked as tainted

  sprintf(buf, s); // warn: untrusted data as a format string
}
</pre></div><div class="separator"></div>
<div class="example"><pre>
void test() {
  size_t ts;
  scanf("%zd", &ts); // 'ts' marked as tainted
  int *p = (int *)malloc(ts * sizeof(int));
    // warn: untrusted data as bufer size
}
</pre></div></div></td></tr>

</tbody></table>

<!--------------------------- unix alpha -------------------------------------->
<h3 id="unix_alpha_checkers">Unix Alpha Checkers</h3>
<table class="checkers">
<colgroup><col class="namedescr"><col class="example"></colgroup>
<thead><tr><td>Name, Description</td><td>Example</td></tr></thead>

<tbody>
<tr><td><div class="namedescr expandable"><span class="name">
alpha.unix.Chroot</span><span class="lang">
(C)</span><div class="descr">
Check improper use of <code>chroot</code>.</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
void f();

void test() {
  chroot("/usr/local");
  f(); // warn: no call of chdir("/") immediately after chroot
}
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.unix.MallocWithAnnotations</span><span class="lang">
(C)</span><div class="descr">
Check for memory leaks, double free, and use-after-free problems. Assumes that
all user-defined functions which might free a pointer are
annotated.</div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
void __attribute((ownership_returns(malloc))) *my_malloc(size_t);

void test() {
  int *p = my_malloc(1);
} // warn: potential leak
</pre></div><div class="separator"></div>
<div class="example"><pre>
void __attribute((ownership_returns(malloc))) *my_malloc(size_t);
void __attribute((ownership_takes(malloc, 1))) my_free(void *);

void test() {
  int *p = my_malloc(1);
  my_free(p);
  my_free(p); // warn: attempt to free released
}
</pre></div><div class="separator"></div>
<div class="example"><pre>
void __attribute((ownership_returns(malloc))) *my_malloc(size_t);
void __attribute((ownership_holds(malloc, 1))) my_hold(void *);

void test() {
  int *p = my_malloc(1);
  my_hold(p);
  free(p); // warn: attempt to free non-owned memory
}
</pre></div><div class="separator"></div>
<div class="example"><pre>
void __attribute((ownership_takes(malloc, 1))) my_free(void *);

void test() {
  int *p = malloc(1);
  my_free(p);
  *p = 1; // warn: use after free
}
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.unix.PthreadLock</span><span class="lang">
(C)</span><div class="descr">
Simple lock -> unlock checker; applies to:<div class=functions>
pthread_mutex_lock<br>
pthread_rwlock_rdlock<br>
pthread_rwlock_wrlock<br>
lck_mtx_lock<br>
lck_rw_lock_exclusive<br>
lck_rw_lock_shared<br>
pthread_mutex_trylock<br>
pthread_rwlock_tryrdlock<br>
pthread_rwlock_tryrwlock<br>
lck_mtx_try_lock<br>
lck_rw_try_lock_exclusive<br>
lck_rw_try_lock_shared<br>
pthread_mutex_unlock<br>
pthread_rwlock_unlock<br>
lck_mtx_unlock<br>
lck_rw_done</div></div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
pthread_mutex_t mtx;

void test() {
  pthread_mutex_lock(&mtx);
  pthread_mutex_lock(&mtx);
    // warn: this lock has already been acquired
}
</pre></div><div class="separator"></div>
<div class="example"><pre>
lck_mtx_t lck1, lck2;

void test() {
  lck_mtx_lock(&lck1);
  lck_mtx_lock(&lck2);
  lck_mtx_unlock(&lck1);
    // warn: this was not the most recently acquired lock
}
</pre></div><div class="separator"></div>
<div class="example"><pre>
lck_mtx_t lck1, lck2;

void test() {
  if (lck_mtx_try_lock(&lck1) == 0)
    return;

  lck_mtx_lock(&lck2);
  lck_mtx_unlock(&lck1);
    // warn: this was not the most recently acquired lock
}
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.unix.SimpleStream</span><span class="lang">
(C)</span><div class="descr">
Check for misuses of stream APIs:<div class=functions>
fopen<br>
fclose</div>(demo checker, the subject of the demo
(<a href="http://llvm.org/devmtg/2012-11/Zaks-Rose-Checker24Hours.pdf">Slides</a>
,<a href="http://llvm.org/devmtg/2012-11/videos/Zaks-Rose-Checker24Hours.mp4">Video</a>)
by Anna Zaks and Jordan Rose presented at the <a href="http://llvm.org/devmtg/2012-11/">
2012 LLVM Developers' Meeting).</a></div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
void test() {
  FILE *F = fopen("myfile.txt", "w");
} // warn: opened file is never closed
</pre></div><div class="separator"></div>
<div class="example"><pre>
void test() {
  FILE *F = fopen("myfile.txt", "w");

  if (F)
    fclose(F);

  fclose(F); // warn: closing a previously closed file stream
}
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.unix.Stream</span><span class="lang">
(C)</span><div class="descr">
Check stream handling functions:<div class=functions>fopen<br>
tmpfile<br>
fclose<br>
fread<br>
fwrite<br>
fseek<br>
ftell<br>
rewind<br>
fgetpos<br>
fsetpos<br>
clearerr<br>
feof<br>
ferror<br>
fileno</div></div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
void test() {
  FILE *p = fopen("foo", "r");
} // warn: opened file is never closed
</pre></div><div class="separator"></div>
<div class="example"><pre>
void test() {
  FILE *p = fopen("foo", "r");
  fseek(p, 1, SEEK_SET); // warn: stream pointer might be NULL
  fclose(p);
}
</pre></div><div class="separator"></div>
<div class="example"><pre>
void test() {
  FILE *p = fopen("foo", "r");

  if (p)
    fseek(p, 1, 3);
     // warn: third arg should be SEEK_SET, SEEK_END, or SEEK_CUR

  fclose(p);
}
</pre></div><div class="separator"></div>
<div class="example"><pre>
void test() {
  FILE *p = fopen("foo", "r");
  fclose(p);
  fclose(p); // warn: already closed
}
</pre></div><div class="separator"></div>
<div class="example"><pre>
void test() {
  FILE *p = tmpfile();
  ftell(p); // warn: stream pointer might be NULL
  fclose(p);
}
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.unix.cstring.BufferOverlap</span><span class="lang">
(C)</span><div class="descr">
Checks for overlap in two buffer arguments; applies to:<div class=functions>
memcpy<br>
mempcpy</div></div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
void test() {
  int a[4] = {0};
  memcpy(a + 2, a + 1, 8); // warn
}
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.unix.cstring.NotNullTerminated</span><span class="lang">
(C)</span><div class="descr">
Check for arguments which are not null-terminated strings; applies
to:<div class=functions>
strlen<br>
strnlen<br>
strcpy<br>
strncpy<br>
strcat<br>
strncat</div></div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
void test() {
  int y = strlen((char *)&test); // warn
}
</pre></div></div></td></tr>


<tr><td><div class="namedescr expandable"><span class="name">
alpha.unix.cstring.OutOfBounds</span><span class="lang">
(C)</span><div class="descr">
Check for out-of-bounds access in string functions; applies
to:<div class=functions>
strncopy<br>
strncat</div></div></div></td>
<td><div class="exampleContainer expandable">
<div class="example"><pre>
void test(char *y) {
  char x[4];
  if (strlen(y) == 4)
    strncpy(x, y, 5); // warn
}
</pre></div></div></td></tr>

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