linux-kernel - Re: [PATCH] reiserfs: fix code unwinding with clang

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Date:   Thu, 18 Jul 2019 08:20:45 -0700
From:   Joe Perches <joe@...ches.com>
To:     Arnd Bergmann <arnd@...db.de>, Jan Kara <jack@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     reiserfs-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH] reiserfs: fix code unwinding with clang

On Thu, 2019-07-18 at 15:49 +0200, Arnd Bergmann wrote:
> Building reiserfs with clang leads to objtool warnings about a part of the
> unreachable code that may confuse the ORC unwinder:
> 
> fs/reiserfs/ibalance.o: warning: objtool: balance_internal()+0xe8f: stack state mismatch: cfa1=7+240 cfa2=7+248
> fs/reiserfs/ibalance.o: warning: objtool: internal_move_pointers_items()+0x36f: stack state mismatch: cfa1=7+152 cfa2=7+144
> fs/reiserfs/lbalance.o: warning: objtool: leaf_cut_from_buffer()+0x58b: stack state mismatch: cfa1=7+128 cfa2=7+112
> fs/reiserfs/lbalance.o: warning: objtool: leaf_copy_boundary_item()+0x7a9: stack state mismatch: cfa1=7+104 cfa2=7+96
> fs/reiserfs/lbalance.o: warning: objtool: leaf_copy_items_entirely()+0x3d2: stack state mismatch: cfa1=7+120 cfa2=7+128
> fs/reiserfs/do_balan.o: warning: objtool: replace_key()+0x158: stack state mismatch: cfa1=7+40 cfa2=7+56
> fs/reiserfs/do_balan.o: warning: objtool: balance_leaf()+0x2791: stack state mismatch: cfa1=7+176 cfa2=7+192
> 
> Reword this to use the regular BUG() call directly from the original code
> location, since objtool finds the generated object code more reasonable.
> 
> This will likely get fixed in a future clang release, but in the meantime
> the workaround helps us build cleanly with existing releases.

The original code read better.

This is kinda a gross solution that should probably be
commented on in the code rather than just the commit message.

> diff --git a/fs/reiserfs/prints.c b/fs/reiserfs/prints.c
[]
> @@ -387,7 +387,6 @@ void __reiserfs_panic(struct super_block *sb, const char *id,
>  	else
>  		printk(KERN_WARNING "REISERFS panic: %s%s%s: %s\n",
>  		      id ? id : "", id ? " " : "", function, error_buf);
> -	BUG();
>  }
>  
>  void __reiserfs_error(struct super_block *sb, const char *id,
> @@ -397,8 +396,10 @@ void __reiserfs_error(struct super_block *sb, const char *id,
>  
>  	BUG_ON(sb == NULL);
>  
> -	if (reiserfs_error_panic(sb))
> +	if (reiserfs_error_panic(sb)) {
>  		__reiserfs_panic(sb, id, function, error_buf);
> +		BUG();
> +	}
>  
>  	if (id && id[0])
>  		printk(KERN_CRIT "REISERFS error (device %s): %s %s: %s\n",
> diff --git a/fs/reiserfs/reiserfs.h b/fs/reiserfs/reiserfs.h
> index e5ca9ed79e54..f5bd17ee21f6 100644
> --- a/fs/reiserfs/reiserfs.h
> +++ b/fs/reiserfs/reiserfs.h
> @@ -3185,10 +3185,9 @@ void unfix_nodes(struct tree_balance *);
>  
>  /* prints.c */
>  void __reiserfs_panic(struct super_block *s, const char *id,
> -		      const char *function, const char *fmt, ...)
> -    __attribute__ ((noreturn));
> +		      const char *function, const char *fmt, ...);
>  #define reiserfs_panic(s, id, fmt, args...) \
> -	__reiserfs_panic(s, id, __func__, fmt, ##args)
> +	do { __reiserfs_panic(s, id, __func__, fmt, ##args); BUG(); } while (0)
>  void __reiserfs_error(struct super_block *s, const char *id,
>  		      const char *function, const char *fmt, ...);
>  #define reiserfs_error(s, id, fmt, args...) \