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From: "dmalcolm at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug analyzer/108806] New: -Wanalyzer-null-dereference false
 positives due to not handling bitmasks
Date: Wed, 15 Feb 2023 16:36:44 +0000
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X-Bugzilla-Version: 13.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108806

            Bug ID: 108806
           Summary: -Wanalyzer-null-dereference false positives due to not
                    handling bitmasks
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: analyzer
          Assignee: dmalcolm at gcc dot gnu.org
          Reporter: dmalcolm at gcc dot gnu.org
            Blocks: 108562
  Target Milestone: ---

Created attachment 54470
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D54470&action=3Dedit
Reproducer

Trunk:    https://godbolt.org/z/77EbbPEW5
GCC 12.2: https://godbolt.org/z/o8bbMhPxW
GCC 11.3: https://godbolt.org/z/o4dK3zn3b
GCC 10.4: https://godbolt.org/z/GzEqzMMjW

Lots of false positives of the form:

<source>: In function 'omap2_inth_read':
<source>:75:18: warning: dereference of NULL 'bank' [CWE-476]
[-Wanalyzer-null-dereference]
   75 |       return bank->inputs;
      |              ~~~~^~~~~~~~
  'omap2_inth_read': events 1-6
    |
    |   40 |   struct omap_intr_handler_bank_s* bank =3D NULL;
    |      |                                    ^~~~
    |      |                                    |
    |      |                                    (1) 'bank' is NULL
    |   41 |=20
    |   42 |   if ((offset & 0xf80) =3D=3D 0x80) {
    |      |      ~=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20
    |      |      |
    |      |      (2) following 'false' branch...
    |......
    |   52 |   switch (offset) {
    |      |   ~~~~~~=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20
    |      |   |
    |      |   (3) ...to here
    |      |   (4) following 'case 128:' branch...
    |......
    |   74 |     case 0x80:
    |      |     ~~~~=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20
    |      |     |
    |      |     (5) ...to here
    |   75 |       return bank->inputs;
    |      |              ~~~~~~~~~~~~=20=20=20=20=20=20=20=20=20=20=20
    |      |                  |
    |      |                  (6) dereference of NULL 'bank'
    |

where if offset =3D=3D 128, then the:

    |   42 |   if ((offset & 0xf80) =3D=3D 0x80) {
    |      |      ~=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20
    |      |      |
    |      |      (2) following 'false' branch...
    |......
    |   52 |   switch (offset) {
    |      |   ~~~~~~=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20
    |      |   |
    |      |   (3) ...to here

edge is impossible, and "bank" will have been properly initialized.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108562
[Bug 108562] [meta-bug] tracker bug for issues with -Wanalyzer-null-derefer=
ence=