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[for-2.8,v2,2/2] loader: fix undefined behavior in rom_order_compare()

Message ID 20161129195533.23113-3-lersek@redhat.com
State Superseded
Headers show

Commit Message

Laszlo Ersek Nov. 29, 2016, 7:55 p.m. UTC 
According to ISO C99 / N1256 (referenced in HACKING):

> 6.5.8 Relational operators

>

> 4 For the purposes of these operators, a pointer to an object that is

>   not an element of an array behaves the same as a pointer to the first

>   element of an array of length one with the type of the object as its

>   element type.

>

> 5 When two pointers are compared, the result depends on the relative

>   locations in the address space of the objects pointed to. If two

>   pointers to object or incomplete types both point to the same object,

>   or both point one past the last element of the same array object, they

>   compare equal. If the objects pointed to are members of the same

>   aggregate object, pointers to structure members declared later compare

>   greater than pointers to members declared earlier in the structure,

>   and pointers to array elements with larger subscript values compare

>   greater than pointers to elements of the same array with lower

>   subscript values. All pointers to members of the same union object

>   compare equal. If the expression /P/ points to an element of an array

>   object and the expression /Q/ points to the last element of the same

>   array object, the pointer expression /Q+1/ compares greater than /P/.

>   In all other cases, the behavior is undefined.


Our AddressSpace objects are allocated generally individually, and kept in
the "address_spaces" linked list, so we mustn't compare their addresses
with relops.

Convert the pointers subjected to the relop in rom_order_compare() to
"uintptr_t":

> 7.18.1.4 Integer types capable of holding object pointers

>

> 1 [...]

>

>   The following type designates an unsigned integer type with the

>   property that any valid pointer to void can be converted to this type,

>   then converted back to pointer to void, and the result will compare

>   equal to the original pointer:

>

>   /uintptr_t/

>

>   These types are optional.


Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Alistair Francis <alistair.francis@xilinx.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: qemu-devel@nongnu.org
Fixes: 3e76099aacb4dae0d37ebf95305369e03d1491e6
Signed-off-by: Laszlo Ersek <lersek@redhat.com>

Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>

---

Notes:
    v2:
    - fix checkpatch error (also verify with the script)
    - pick up R-b from Alistair

 hw/core/loader.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

-- 
2.9.2
diff mbox

Patch

diff --git a/hw/core/loader.c b/hw/core/loader.c
index c0d645a87134..45742494e6fd 100644
--- a/hw/core/loader.c
+++ b/hw/core/loader.c
@@ -818,7 +818,7 @@  static QTAILQ_HEAD(, Rom) roms = QTAILQ_HEAD_INITIALIZER(roms);
 
 static inline bool rom_order_compare(Rom *rom, Rom *item)
 {
-    return (rom->as > item->as) ||
+    return ((uintptr_t)(void *)rom->as > (uintptr_t)(void *)item->as) ||
            (rom->as == item->as && rom->addr >= item->addr);
 }