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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/108552] Linux i386 kernel 5.14 memory
 corruption for pre_compound_page() when gcov is enabled
Date: Sun, 29 Jan 2023 10:08:32 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108552

--- Comment #40 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Jan Hubicka from comment #39)
> I was wonering if we should not provide flag to turn all counts
> volatile.   That way we will still have race conditions on their updates
> (and it would be chepaer than atomic) but we won't run into such wrong
> code issues nor large profile mismatches.

Yes, see above.  Or a mode in which we would just avoid hoisting and sinking
the gcov vars but keep them non-volatile.  Or both.
But I guess it would be nice to get Vlad's patch into trunk and release
branches for now (perhaps with an extra check for startswith "__gcov" on
DECL_NAME, so that we don't do it for the Fortran tokens).

As for the patch, just small nits, I think get_base_address returns always
non-NULL, so it could be
      if (tree expr =3D MEM_EXPR (res))
        {
          expr =3D get_base_address (expr);
          if (VAR_P (expr)
              && DECL_NONALIASED (expr)
              && DECL_NAME (expr))
            {
              const char *name =3D IDENTIFIER_POINTER (DECL_NAME (expr));
              /* Don't reread coverage counters from memory, if single
                 update model is used in threaded code, other threads
                 could change the counters concurrently.  See PR108552.  */
              if (startswith (name, "__gcov"))
                return x;
            }
        }=