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From: "raimue at codingfarm dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug analyzer/106473] New: -Wanalyzer-malloc-leak false positive
 regression when returning heap-allocation through nested pointers
Date: Fri, 29 Jul 2022 07:13:38 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106473

            Bug ID: 106473
           Summary: -Wanalyzer-malloc-leak false positive regression when
                    returning heap-allocation through nested pointers
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: analyzer
          Assignee: dmalcolm at gcc dot gnu.org
          Reporter: raimue at codingfarm dot de
  Target Milestone: ---

Source:

void foo(char **args[], int *argc) {
    *argc =3D 1;
    (*args)[0] =3D __builtin_malloc(42);
}


Compiler output:

$ gcc-12 -Wall -fanalyzer -c -o foo.o foo.c
foo.c: In function 'foo':
foo.c:4:1: warning: leak of '<unknown>' [CWE-401] [-Wanalyzer-malloc-leak]
    4 | }
      | ^
  'foo': events 1-2
    |
    |    3 |     (*args)[0] =3D __builtin_malloc(42);
    |      |                  ^~~~~~~~~~~~~~~~~~~~
    |      |                  |
    |      |                  (1) allocated here
    |    4 | }
    |      | ~=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
    |      | |
    |      | (2) '<unknown>' leaks here; was allocated at (1)
    |


Notes:
This is only reported with the write to argc happening first, which should =
be
considered completely unrelated to args. Reordering the two statements reso=
lves
the analyzer report.


Tested versions:

gcc 10.3: FAIL
gcc 11.2: OK
gcc 12.0: FAIL

I therefore consider this a regression as it was not reported by gcc 11.


Compiler Explorer link:
  https://gcc.godbolt.org/z/zGanPa3fs=