[Bug c++/47634] New: Incorrect checking of attribute format printf on constructor of derived class with virtual base

[Bug c++/47634] New: Incorrect checking of attribute format printf on constructor of derived class with virtual base

[dan at randomdan dot homeip.net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47634

           Summary: Incorrect checking of attribute format printf on
                    constructor of derived class with virtual base
           Product: gcc
           Version: 4.4.5
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: dan@randomdan.homeip.net


Given the below code, gcc produces the following warnings:

exception.cpp: In function 'int main(int, char**)':
exception.cpp:28: warning: format not a string literal and no format arguments

Changing the __attribute__ on VDerived's constructor to be the same as Derived
produces the following error:
exception.cpp:9: error: format string argument not a string type

Compiled simply with:
g++ exception.cpp

class Base {
    public:
        Base() {
        }
};

class VDerived : public virtual Base {
    public:
        VDerived(int x, const char * f, ...) __attribute__((format(printf, 5,
6)));
};

class Derived : public Base {
    public:
        Derived(int x, const char * f, ...) __attribute__((format(printf, 3,
4)));
};

VDerived::VDerived(int x, const char * f, ...)
{
}

Derived::Derived(int x, const char * f, ...)
{
}

int
main(int, char **)
{
    throw VDerived(1, "%s %d", "foo", 1);
    throw Derived(1, "%s %d", "bar", 1);
}

[Bug c++/47634] Incorrect checking of attribute format printf on constructor of derived class with virtual base

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47634

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=101833

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I have not exactly looked into this bug but I did find an ICE dealing with the
code: PR 101833.

[Bug c++/47634] Incorrect checking of attribute format printf on constructor of derived class with virtual base

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47634

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mpolacek at gcc dot gnu.org
     Ever confirmed|0                           |1
           Assignee|unassigned at gcc dot gnu.org      |mpolacek at gcc dot gnu.org
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2022-03-31

[Bug c++/47634] Incorrect checking of attribute format printf on constructor of derived class with virtual base

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47634

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:0c723bb4be2a67657828b692997855afcdc5d286

commit r13-167-g0c723bb4be2a67657828b692997855afcdc5d286
Author: Marek Polacek <polacek@redhat.com>
Date:   Thu Mar 31 18:31:39 2022 -0400

    c, c++: attribute format on a ctor with a vbase [PR101833, PR47634]

    Attribute format takes three arguments: archetype, string-index, and
    first-to-check.  The last two specify the position in the function
    parameter list.  r63030 clarified that "Since non-static C++ methods have
    an implicit this argument, the arguments of such methods should be counted
    from two, not one, when giving values for string-index and first-to-check."
    Therefore one has to write

      struct D {
        D(const char *, ...) __attribute__((format(printf, 2, 3)));
      };

    However -- and this is the problem in this PR -- ctors with virtual
    bases also get two additional parameters: the in-charge parameter and
    the VTT parameter (added in maybe_retrofit_in_chrg).  In fact we'll end up
    with two clones of the ctor: an in-charge and a not-in-charge version (see
    build_cdtor_clones).  That means that the argument position the user
    specified in the attribute argument will refer to different arguments,
    depending on which constructor we're currently dealing with.  This can
    cause a range of problems: wrong errors, confusing warnings, or crashes.

    This patch corrects that; for C we don't have to do anything, and in C++
    we can use num_artificial_parms_for.  It would be wrong to rewrite the
    attributes the user supplied, so I've changed POS to be passed by
    reference so that we don't have to change all the call sites of
    positional_argument and we still get the default_conversion adjustment.

    Attribute format_arg is not affected, because it requires that the
    function returns "const char *" which will never be the case for cdtors.

            PR c++/101833
            PR c++/47634

    gcc/c-family/ChangeLog:

            * c-attribs.cc (positional_argument): Pass POS by reference.  Deal
            with FN being either a function declaration or function type.  Use
            maybe_adjust_arg_pos_for_attribute.
            * c-common.cc (check_function_arguments): Maybe pass FNDECL down to
            check_function_format.
            * c-common.h (maybe_adjust_arg_pos_for_attribute): Declare.
            (positional_argument): Adjust.
            * c-format.cc (get_constant): Rename to ...
            (validate_constant): ... this.  Take EXPR by reference.  Return
bool
            instead of tree.
            (handle_format_arg_attribute): Don't overwrite FORMAT_NUM_EXPR by
the
            return value of validate_constant.
            (decode_format_attr): Don't overwrite FORMAT_NUM_EXPR and
            FIRST_ARG_NUM_EXPR by the return value of validate_constant.
            (check_function_format): Adjust a parameter name.
            (handle_format_attribute): Maybe pass FNDECL down to
decode_format_attr.

    gcc/c/ChangeLog:

            * c-objc-common.cc (maybe_adjust_arg_pos_for_attribute): New.

    gcc/cp/ChangeLog:

            * tree.cc (maybe_adjust_arg_pos_for_attribute): New.

    gcc/ChangeLog:

            * tree-core.h (struct attribute_spec): Update comment for HANDLER.

    gcc/testsuite/ChangeLog:

            * g++.dg/ext/attr-format-arg1.C: New test.
            * g++.dg/ext/attr-format1.C: New test.
            * g++.dg/ext/attr-format2.C: New test.
            * g++.dg/ext/attr-format3.C: New test.

[Bug c++/47634] Incorrect checking of attribute format printf on constructor of derived class with virtual base

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47634

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Fixed for GCC 13.