[Bug c++/111742] New: Misaligned generated code with MI using aligned virtual base

[Bug c++/111742] New: Misaligned generated code with MI using aligned virtual base

[cuzdav at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111742

            Bug ID: 111742
           Summary: Misaligned generated code with MI using aligned
                    virtual base
           Product: gcc
           Version: 13.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: cuzdav at gmail dot com
  Target Milestone: ---

Generated code is misaligned (and crashes in slightly more complex code), in
trunk all the way back to gcc 8.1, when built in c++11 or higher, with O3. 
(Linux, x86)

Complete code:
//////////////////////////////////////////
struct X {
  void * a = nullptr;
  void * b = nullptr;
};

struct alignas(16) AlignedData { };

struct A : virtual AlignedData {
  X xxx;
};

struct B : virtual AlignedData {};

struct Test : B, A {};

Test* t = new Test;

int main() {}
//////////////////////////////////////////

Compiler Explorer demo:
https://godbolt.org/z/aodTdaedW

Running with UB-san reports this:
/app/example.cpp:14:8: runtime error: constructor call on misaligned address
0x00000227f2b8 for type 'struct A', which requires 16 byte alignment
0x00000227f2b8: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00
00 00 00  00 00 00 00
              ^ 
/app/example.cpp:8:8: runtime error: member access within misaligned address
0x00000227f2b8 for type 'struct A', which requires 16 byte alignment
0x00000227f2b8: note: pointer points here
 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00
00 00 00  00 00 00 00
              ^

[Bug c++/111742] Misaligned generated code with MI using aligned virtual base

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111742

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
It is just a santizer issue. Dup of bug 83780.

*** This bug has been marked as a duplicate of bug 83780 ***

[Bug c++/111742] Misaligned generated code with MI using aligned virtual base

[cuzdav at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111742

--- Comment #2 from Chris Uzdavinis <cuzdav at gmail dot com> ---
No, this is not a ubsan report.
Code *crashes* and I thought showing the UBsan warning was enough to
demonstrate it.
A minimal change to make the code crash instead of just report ubsan errors:


struct X {
  void * a = nullptr;
  void * b = nullptr;
};

struct alignas(16) AlignedData { };

struct A : virtual AlignedData {
    int x = 0;       // << ********add this
  X xxx;
    int& ref = x;    // << ********and this
};

struct B : virtual AlignedData {};

struct Test : B, A {};

Test* t = new Test;

int main() {}


*** SEGFAULT ***

https://godbolt.org/z/f57vs7jxP

[Bug c++/111742] Misaligned generated code with MI using aligned virtual base

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111742

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Then it is a dup of bug 71644.

*** This bug has been marked as a duplicate of bug 71644 ***