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From: "pshevchuk at pshevchuk dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/114806] New: placement new doesn't check array length
Date: Mon, 22 Apr 2024 15:58:43 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 13.2.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114806

            Bug ID: 114806
           Summary: placement new doesn't check array length
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pshevchuk at pshevchuk dot com
  Target Milestone: ---

Created attachment 58008
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D58008&action=3Dedit
Example code but as attachment

#include <new>
#include <cstdio>

int main()
{
    int sz =3D -1;
    char buf[9];
    char* res =3D new (buf) char[sz];
    std::puts(res =3D=3D (char*) nullptr? "correct" : "wrong");
}

This program should output "correct", since:

expr.new.9: array bound is erroneous since it's less than zero before
conversion to std::size_t (9.1)

expr.new.9.5.1: the placement new is nothrow, so the result of this operati=
on
must be nullptr. It isn't

Curiously, if you replace the allocated type with an array of ints, it will
incorrectly throw the std::bad_array_new_length exception instead of return=
ing
nullptr.

Seems to be present in gcc 8.2 and in gcc13 too=