[Bug ada/123832] New: Stack corruption when combining "&" and 'Image

[liam at liampwll dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123832

            Bug ID: 123832
           Summary: Stack corruption when combining "&" and 'Image
           Product: gcc
           Version: 15.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ada
          Assignee: unassigned at gcc dot gnu.org
          Reporter: liam at liampwll dot com
                CC: dkm at gcc dot gnu.org
  Target Milestone: ---

I'm not sure of the exact cause here, but the below trivial program seems to
cause some kind of stack corruption, specifically it overwrites an address
which ada.strings.text_buffers.unbounded.buffer_type.Finalize reads and causes
a segfault. I have also seen this silently corrupt data in a larger program.
This occurs on 16, 15.2, 14.3, 13.4, and 12.5.

pragma Ada_2022;

procedure Example is
   type T is array (1 .. 13) of Integer;

   function "&" (Left : T; Right : T) return T
   is (others => 2);
   --  Finalize will attempt to read at address 0xA when above is 2.
   --  That changes to 0xB when above is 3.

   function To_Virtual_String (Item : String) return T
   is (others => 0);

   procedure F (S : T) is null;

   X : array (1 .. 1) of Integer := [others => 0];
begin
   F ((others => 0) & To_Virtual_String (X'Image));
end Example;