linux-kernel - [PATCH] fsnotify: avoid gcc-10 zero-length-bounds warning

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Date:   Tue,  5 May 2020 16:30:09 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Alexander Viro <viro@...iv.linux.org.uk>
Cc:     Arnd Bergmann <arnd@...db.de>,
        "Gustavo A . R . Silva" <gustavo@...eddedor.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Jan Kara <jack@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Amir Goldstein <amir73il@...il.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] fsnotify: avoid gcc-10 zero-length-bounds warning

gcc-10 warns about accesses into the f_handle[] zero-length array.

fs/notify/fdinfo.c: In function 'show_mark_fhandle':
fs/notify/fdinfo.c:66:47: error: array subscript 'i' is outside the bounds of an interior zero-length array 'unsigned char[0]' [-Werror=zero-length-bounds]
   66 |   seq_printf(m, "%02x", (int)f.handle.f_handle[i]);
      |                              ~~~~~~~~~~~~~~~~~^~~
In file included from fs/notify/fdinfo.c:3:
include/linux/fs.h:988:16: note: while referencing 'f_handle'
  988 |  unsigned char f_handle[0];
      |                ^~~~~~~~

This is solved by using a flexible array instead.

Cc: Gustavo A. R. Silva <gustavo@...eddedor.com>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
Gustavo has done the same thing as part of a treewide change, but keeping
this separate lets us backport it to stable kernels more easily later.
---
 include/linux/fs.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 8690dc56e883..b229c55a8232 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -986,7 +986,7 @@ struct file_handle {
 	__u32 handle_bytes;
 	int handle_type;
 	/* file identifier */
-	unsigned char f_handle[0];
+	unsigned char f_handle[];
 };
 
 static inline struct file *get_file(struct file *f)
-- 
2.26.0