Date:   Thu, 8 Aug 2019 22:45:34 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     kbuild test robot <lkp@...el.com>
Cc:     kbuild-all@...org, Josh Poimboeuf <jpoimboe@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [arnd-playground:randconfig-5.3-rc2 32/347] fs/reiserfs/prints.o:
 warning: objtool: __reiserfs_error()+0x80: unreachable instruction

On Thu, Aug 8, 2019 at 9:06 PM kbuild test robot <lkp@...el.com> wrote:
>
> tree:   https://kernel.googlesource.com/pub/scm/linux/kernel/git/arnd/playground.git randconfig-5.3-rc2
> head:   bfe9aede7372c8310a9bf31963460c9dd11d1f82
> commit: 97919a3ec80e9841c4bbac14a80e8b9d482666d4 [32/347] [SUBMITTED 20190718] reiserfs: fix code unwinding with clang
> config: x86_64-lkp (attached as .config)
> compiler: gcc-7 (Debian 7.4.0-10) 7.4.0
> reproduce:
>         git checkout 97919a3ec80e9841c4bbac14a80e8b9d482666d4
>         # save the attached .config to linux build tree
>         make ARCH=x86_64
>
> If you fix the issue, kindly add following tag
> Reported-by: kbuild test robot <lkp@...el.com>
>
> All warnings (new ones prefixed by >>):
>
> >> fs/reiserfs/namei.o: warning: objtool: entry_points_to_object()+0x117: unreachable instruction
> --
> >> fs/reiserfs/do_balan.o: warning: objtool: get_FEB()+0x55: unreachable instruction
> >> fs/reiserfs/prints.o: warning: objtool: __reiserfs_error()+0x80: unreachable instruction
> >> fs/reiserfs/lbalance.o: warning: objtool: leaf_move_items()+0x210: unreachable instruction
> >> fs/reiserfs/fix_node.o: warning: objtool: create_virtual_node()+0x295: unreachable instruction
> >> fs/reiserfs/inode.o: warning: objtool: reiserfs_update_sd_size()+0x26b: unreachable instruction
> >> fs/reiserfs/ibalance.o: warning: objtool: balance_internal()+0x30d: unreachable instruction
> >> fs/reiserfs/stree.o: warning: objtool: reiserfs_cut_from_item()+0x239: unreachable instruction
> >> fs/reiserfs/tail_conversion.o: warning: objtool: direct2indirect()+0x29c: unreachable instruction
> >> fs/reiserfs/item_ops.o: warning: objtool: direntry_check_left()+0x5d: unreachable instruction
> >> fs/reiserfs/journal.o: warning: objtool: flush_commit_list()+0x552: unreachable instruction

Great fun. The patch I did was my workaround for a related problem with clang,
see below.

Josh, is this warning above something you are interested in? I don't
think it happens in mainline, but it could happen anywhere. I think
the patch below can be dropped once clang is fixed, but I have so far
been unable to build a new compiler for testing.

       Arnd

commit 97919a3ec80e9841c4bbac14a80e8b9d482666d4
Author: Arnd Bergmann <arnd@...db.de>
Date:   Fri Jul 12 16:19:52 2019 +0200

    [SUBMITTED 20190718] reiserfs: fix code unwinding with clang

    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.

    Link: https://groups.google.com/d/msgid/clang-built-linux/20190712135755.7qa4wxw3bfmwn5rp%40treble
    Signed-off-by: Arnd Bergmann <arnd@...db.de>

diff --git a/fs/reiserfs/prints.c b/fs/reiserfs/prints.c
index 9fed1c05f1f4..da996eaaebac 100644
--- 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...) \

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