[Bug sanitizer/113304] New: zero-length array and bound checking error

[Bug sanitizer/113304] New: zero-length array and bound checking error

[marcandre.lureau at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113304

            Bug ID: 113304
           Summary: zero-length array and bound checking error
           Product: gcc
           Version: 13.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: unassigned at gcc dot gnu.org
          Reporter: marcandre.lureau at gmail dot com
                CC: dodji at gcc dot gnu.org, dvyukov at gcc dot gnu.org,
                    jakub at gcc dot gnu.org, kcc at gcc dot gnu.org, marxin at gcc dot gnu.org
  Target Milestone: ---

gcc (GCC) 13.2.1 20231205 (Red Hat 13.2.1-6)

gcc -fsanitize=bounds-strict -lubsan test.c

test.c:6:11: runtime error: index 3 out of bounds for type 'int [*]'

typedef struct BN {
    int d[0];
} BN;

void test(BN *foo) {
    foo->d[3] = 0;
}

int main(int argc, char *argv[])
{
    struct BN {
        int d[4];
    } foo;

    test((BN *)&foo);

    return 0;
}



This coding style is used in bignum libraries, such as libtpms BN
implementation. Is this incompatible with bounds-strict usage?

[Bug sanitizer/113304] zero-length array and bound checking error

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113304

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |documentation

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
-fsanitize=bounds-strict is the basically the same as `-fsanitize=bounds
-fstrict-flex-arrays=3` which says [0] is not a flexiable array either.

This should be better documented though.  Even -fstrict-flex-arrays needs some
slightly better documentation, maybe examples will help.

[Bug sanitizer/113304] zero-length array and bound checking error

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113304

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2024-01-10
             Status|UNCONFIRMED                 |NEW

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note -fsanitize=bounds-strict ignores the attribute strict_flex_array too which
is definitely not documented.

Confirmed for the documentation improvement.