Re: [PATCH] Avoid depending on destructor order

[Jason Merrill <jason@redhat.com>]

On 9/19/22 12:20, Thomas Neumann wrote:
> In some scenarios (e.g., when mixing gcc and clang code), it can
> happen that frames are deregistered after the lookup structure
> has already been destroyed. That in itself would be fine, but
> it triggers an assert in __deregister_frame_info_bases that
> expects to find the frame.
> 
> To avoid that, we now remember that the btree as already been
> destroyed and disable the assert in that case.

OK.

> libgcc/ChangeLog:
> 
>      * unwind-dw2-fde.c: (release_register_frames) Remember
>      when the btree has been destroyed.
>      (__deregister_frame_info_bases) Disable the assert when
>      shutting down.
> ---
>   libgcc/unwind-dw2-fde.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/libgcc/unwind-dw2-fde.c b/libgcc/unwind-dw2-fde.c
> index 919abfe0664..d237179f4ea 100644
> --- a/libgcc/unwind-dw2-fde.c
> +++ b/libgcc/unwind-dw2-fde.c
> @@ -48,6 +48,7 @@ typedef __UINTPTR_TYPE__ uintptr_type;
>   #include "unwind-dw2-btree.h"
> 
>   static struct btree registered_frames;
> +static bool in_shutdown;
> 
>   static void
>   release_registered_frames (void) __attribute__ ((destructor (110)));
> @@ -57,6 +58,7 @@ release_registered_frames (void)
>     /* Release the b-tree and all frames. Frame releases that happen 
> later are
>      * silently ignored */
>     btree_destroy (&registered_frames);
> +  in_shutdown = true;
>   }
> 
>   static void
> @@ -282,7 +284,7 @@ __deregister_frame_info_bases (const void *begin)
>     __gthread_mutex_unlock (&object_mutex);
>   #endif
> 
> -  gcc_assert (ob);
> +  gcc_assert (in_shutdown || ob);
>     return (void *) ob;
>   }
>