* Re: [PATCH] jfs: avoid undefined behavior from left-shifting by 32 bits
[not found] <1357413561-42508-1-git-send-email-nickolai@csail.mit.edu>
@ 2013-01-07 14:33 ` Dave Kleikamp
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From: Dave Kleikamp @ 2013-01-07 14:33 UTC (permalink / raw)
To: Nickolai Zeldovich; +Cc: linux-kernel, jfs-discussion
On 01/05/2013 01:19 PM, Nickolai Zeldovich wrote:
> Shifting a 32-bit int by 32 bits is undefined behavior in C, and
> results in different behavior on different architectures (e.g., x86
> and PowerPC). diAlloc() in fs/jfs/jfs_imap.c computes a mask using
> 0xffffffffu<<(32-bitno), which can left-shift by 32 bits. To avoid
> unexpected behavior, explicitly check for bitno==0 and use a 0 mask.
Thanks. Pushed to
git://github.com/kleikamp/linux-shaggy.git jfs-next
Shaggy
>
> Signed-off-by: Nickolai Zeldovich <nickolai@csail.mit.edu>
> ---
> fs/jfs/jfs_imap.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/jfs/jfs_imap.c b/fs/jfs/jfs_imap.c
> index 6ba4006..f7e042b 100644
> --- a/fs/jfs/jfs_imap.c
> +++ b/fs/jfs/jfs_imap.c
> @@ -1493,7 +1493,7 @@ int diAlloc(struct inode *pip, bool dir, struct inode *ip)
> /* mask any prior bits for the starting words of the
> * summary map.
> */
> - mask = ONES << (EXTSPERSUM - bitno);
> + mask = (bitno == 0) ? 0 : (ONES << (EXTSPERSUM - bitno));
> inosmap = le32_to_cpu(iagp->inosmap[sword]) | mask;
> extsmap = le32_to_cpu(iagp->extsmap[sword]) | mask;
>
>
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