linux-kernel - [PATCH v2] vfs: bogus warnings in fs/namei.c

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Date:	Thu, 11 Oct 2012 13:20:00 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Jan Kara <jack@...e.cz>, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, arm@...nel.org,
	linux-fsdevel@...r.kernel.org
Subject: [PATCH v2] vfs: bogus warnings in fs/namei.c

The follow_link() function always initializes its *p argument,
or returns an error, but when building with 'gcc -s', the compiler
gets confused by the __always_inline attribute to the function
and can no longer detect where the cookie was initialized.

The solution is to always initialize the pointer from follow_link,
even in the error path. When building with -O2, this has zero impact
on generated code and adds a single instruction in the error path
for a -Os build on ARM.

Without this patch, building with gcc-4.6 through gcc-4.8 and
CONFIG_CC_OPTIMIZE_FOR_SIZE results in:

fs/namei.c: In function 'link_path_walk':
fs/namei.c:649:24: warning: 'cookie' may be used uninitialized in this function [-Wuninitialized]
fs/namei.c:1544:9: note: 'cookie' was declared here
fs/namei.c: In function 'path_lookupat':
fs/namei.c:649:24: warning: 'cookie' may be used uninitialized in this function [-Wuninitialized]
fs/namei.c:1934:10: note: 'cookie' was declared here
fs/namei.c: In function 'path_openat':
fs/namei.c:649:24: warning: 'cookie' may be used uninitialized in this function [-Wuninitialized]
fs/namei.c:2899:9: note: 'cookie' was declared here

Signed-off-by: Arnd Bergmann <arnd@...db.de>

diff --git a/fs/namei.c b/fs/namei.c
index 6d47fac..c1f18e4 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -810,6 +810,7 @@ follow_link(struct path *link, struct nameidata *nd, void **p)
 	return error;
 
 out_put_nd_path:
+	*p = NULL;
 	path_put(&nd->path);
 	path_put(link);
 	return error;
--
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