linux-kernel - Re: [PATCH] unwind deferred: Annotate struct unwind_cache with __counted

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Message-ID: <20251114095734.42b51e6c@gandalf.local.home>
Date: Fri, 14 Nov 2025 09:57:34 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Thorsten Blum <thorsten.blum@...ux.dev>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>, Kees Cook <kees@...nel.org>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] unwind deferred: Annotate struct unwind_cache with
 __counted_by

On Fri, 14 Nov 2025 08:53:32 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> --- a/include/linux/unwind_deferred_types.h
> +++ b/include/linux/unwind_deferred_types.h
> @@ -2,10 +2,14 @@
>  #ifndef _LINUX_UNWIND_USER_DEFERRED_TYPES_H
>  #define _LINUX_UNWIND_USER_DEFERRED_TYPES_H
>  
> +/* Make the cache fit in a 4K page */
> +#define UNWIND_MAX_ENTRIES					\
> +	((SZ_4K - offset_of(struct unwind_cache, entries)) / sizeof(long))
> +
>  struct unwind_cache {
>  	unsigned long		unwind_completed;
>  	unsigned int		nr_entries;
> -	unsigned long		entries[];
> +	unsigned long		entries[UNWIND_MAX_ENTRIES];
>  };
>  

Nope, this fails with:

/work/git/test-linux.git/include/linux/stddef.h:16:33: error: invalid use of undefined type ‘struct unwind_cache’
   16 | #define offsetof(TYPE, MEMBER)  __builtin_offsetof(TYPE, MEMBER)
      |                                 ^~~~~~~~~~~~~~~~~~
/work/git/test-linux.git/include/linux/unwind_deferred_types.h:9:19: note: in expansion of macro ‘offsetof’
    9 |         ((SZ_4K - offsetof(struct unwind_cache, entries)) / sizeof(long))
      |                   ^~~~~~~~
/work/git/test-linux.git/include/linux/unwind_deferred_types.h:14:41: note: in expansion of macro ‘UNWIND_MAX_ENTRIES’
   14 |         unsigned long           entries[UNWIND_MAX_ENTRIES];
      |                                         ^~~~~~~~~~~~~~~~~~

-- Steve