[cfe-dev] Prevent RetainCountChecker from Analyzing Function Bodies when They Have Certain Annotate Attribute

[Malhar Thakkar via cfe-dev]

Dear all,

I wish to prevent the RetainCountChecker from analyzing function bodies if
these functions have certain annotate attributes. Consider the following
example to get a better idea of why I wish to do that.

Below is a small snippet from the Integer Set Library (ISL).

typedef struct {
  int ref;
} isl_basic_map;

__attribute__((cf_returns_retained))
isl_basic_map *isl_basic_map_copy(isl_basic_map *bmap);

__attribute__((cf_returns_retained))
isl_basic_map *isl_basic_map_cow
(__attribute__((cf_consumed)) isl_basic_map *bmap);

void free(void *);

__attribute__((annotate("rc_ownership_trusted_implementation")))
isl_basic_map *isl_basic_map_free
(__attribute__((cf_consumed)) isl_basic_map *bmap) {
  if (!bmap)
    return NULL;

  if (--bmap->ref > 0)
    return NULL;

  free(bmap);
  return NULL;
}

__attribute__((cf_returns_retained))
isl_basic_map *foo
(__attribute__((cf_consumed)) isl_basic_map *bmap) {
  // *After this call, 'temp' has a +1 reference count.*
  isl_basic_map *temp = isl_basic_map_copy(bmap);
  // *After this call, 'bmap' has a +1 reference count.*
  bmap = isl_basic_map_cow(bmap);
  // *After this call, assuming the predicate of the second if branch to be
true, 'bmap' has a +1 reference count.*
  isl_basic_map_free(bmap);
  return temp; *// Object leaked: 'bmap'*
}

While running the RetainCountChecker on the above example, it raises a leak
warning for 'bmap' in function 'foo'. This warning is a true positive from
the checker's perspective in the sense that the reference count of 'bmap'
obtained from 'isl_basic_map_cow' is not decremented(from the checker's
perspective) in 'isl_basic_map_free' even though it takes the argument
'bmap' as '__attribute__((cf_consumed))'.

Actually, '--bmap->ref' does decrement the reference count (from ISL's
perspective). Hence, to prevent such false positives (from ISL's
perspective) to be raised, I wish to prevent the RetainCountChecker to
analyze the bodies of the functions having
'rc_ownership_trusted_implementation' annotate attribute. I want the
checker to just look at the declaration of such functions (and not go
inside their bodies) to get the necessary information about reference
counting.

Could someone suggest me a way to achieve my objective?


Thank you.


Regards,
Malhar Thakkar
ᐧ
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