linux-kernel - [PATCH 10/15] hpfs: avoid gcc-10 zero-length-bounds warning

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Date:   Thu, 30 Apr 2020 23:30:52 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     linux-kernel@...r.kernel.org,
        Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
Cc:     Arnd Bergmann <arnd@...db.de>
Subject: [PATCH 10/15] hpfs: avoid gcc-10 zero-length-bounds warning

gcc-10 now warns about accessing members of a zero-length array
field:

fs/hpfs/anode.c: In function 'hpfs_add_sector_to_btree':
fs/hpfs/anode.c:209:27: error: array subscript 0 is outside the bounds of an interior zero-length array 'struct bplus_internal_node[0]' [-Werror=zero-length-bounds]
  209 |    anode->btree.u.internal[0].down = cpu_to_le32(a);
      |    ~~~~~~~~~~~~~~~~~~~~~~~^~~
In file included from fs/hpfs/hpfs_fn.h:26,
                 from fs/hpfs/anode.c:10:
fs/hpfs/hpfs.h:411:32: note: while referencing 'internal'
  411 |     struct bplus_internal_node internal[0]; /* (internal) 2-word entries giving
      |                                ^~~~~~~~

It would be nice to make it a flexible-array member, but that is not
possible inside of a union, so work around the warnings by adding
a temporary pointer that hides the problem.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 fs/hpfs/anode.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/hpfs/anode.c b/fs/hpfs/anode.c
index c14c9a035ee0..55788ca7969f 100644
--- a/fs/hpfs/anode.c
+++ b/fs/hpfs/anode.c
@@ -200,14 +200,17 @@ secno hpfs_add_sector_to_btree(struct super_block *s, secno node, int fnod, unsi
 		brelse(bh);
 		a = na;
 		if ((new_anode = hpfs_alloc_anode(s, a, &na, &bh))) {
+			struct bplus_internal_node *internal;
+
 			anode = new_anode;
 			/*anode->up = cpu_to_le32(up != -1 ? up : ra);*/
 			anode->btree.flags |= BP_internal;
 			anode->btree.n_used_nodes = 1;
 			anode->btree.n_free_nodes = 59;
 			anode->btree.first_free = cpu_to_le16(16);
-			anode->btree.u.internal[0].down = cpu_to_le32(a);
-			anode->btree.u.internal[0].file_secno = cpu_to_le32(-1);
+			internal = anode->btree.u.internal;
+			internal->down = cpu_to_le32(a);
+			internal->file_secno = cpu_to_le32(-1);
 			mark_buffer_dirty(bh);
 			brelse(bh);
 			if ((anode = hpfs_map_anode(s, a, &bh))) {
-- 
2.26.0