The patch titled
avoid negative (and full-width) shifts in radix-tree.c
has been added to the -mm tree. Its filename is
avoid-negative-and-full-width-shifts-in-radix-treec.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: avoid negative (and full-width) shifts in radix-tree.c
From: Peter Lund <firefly@xxxxxxxx>
Negative shifts are not allowed in C (the result is undefined). Same thing
with full-width shifts.
It works on most platforms but not on the VAX with gcc 4.0.1 (it results in an
"operand reserved" fault).
Shifting by more than the width of the value on the left is also not
allowed. I think the extra '>> 1' tacked on at the end in the original
code was an attempt to work around that. Getting rid of that is an extra
feature of this patch.
Here's the chapter and verse, taken from the final draft of the C99
standard ("6.5.7 Bitwise shift operators", paragraph 3):
"The integer promotions are performed on each of the operands. The
type of the result is that of the promoted left operand. If the
value of the right operand is negative or is greater than or equal
to the width of the promoted left operand, the behavior is
undefined."
Thank you to Jan-Benedict Glaw, Christoph Hellwig, Maciej Rozycki, Pekka
Enberg, Andreas Schwab, and Christoph Lameter for review. Special thanks
to Andreas for spotting that my fix only removed half the undefined
behaviour.
Signed-off-by: Peter Lund <firefly@xxxxxxxx>
Christoph Lameter <clameter@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: "Maciej W. Rozycki" <macro@xxxxxxxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxxxxxx>
Cc: Andreas Schwab <schwab@xxxxxxx>
Cc: Nick Piggin <nickpiggin@xxxxxxxxxxxx>
Cc: WU Fengguang <wfg@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/radix-tree.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
diff -puN lib/radix-tree.c~avoid-negative-and-full-width-shifts-in-radix-treec lib/radix-tree.c
--- a/lib/radix-tree.c~avoid-negative-and-full-width-shifts-in-radix-treec
+++ a/lib/radix-tree.c
@@ -1049,12 +1049,14 @@ radix_tree_node_ctor(void *node, struct
static __init unsigned long __maxindex(unsigned int height)
{
- unsigned int tmp = height * RADIX_TREE_MAP_SHIFT;
- unsigned long index = (~0UL >> (RADIX_TREE_INDEX_BITS - tmp - 1)) >> 1;
+ unsigned int width = height * RADIX_TREE_MAP_SHIFT;
+ int shift = RADIX_TREE_INDEX_BITS - width;
- if (tmp >= RADIX_TREE_INDEX_BITS)
- index = ~0UL;
- return index;
+ if (shift < 0)
+ return ~0UL;
+ if (shift >= BITS_PER_LONG)
+ return 0UL;
+ return ~0UL >> shift;
}
static __init void radix_tree_init_maxindex(void)
_
Patches currently in -mm which might be from firefly@xxxxxxxx are
avoid-negative-and-full-width-shifts-in-radix-treec.patch
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