[Xen-changelog] [qemu-xen master] loader: fix undefined behavior in rom_order_compare()

[patchbot@xxxxxxx]

commit 1b57bd4f2f4993104a5cb48912435396faa10d58
Author:     Laszlo Ersek <lersek@xxxxxxxxxx>
AuthorDate: Tue Nov 29 20:55:33 2016 +0100
Commit:     Michael S. Tsirkin <mst@xxxxxxxxxx>
CommitDate: Wed Nov 30 04:22:18 2016 +0200

    loader: fix undefined behavior in rom_order_compare()
    
    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@xxxxxxxxxx>
    Cc: Alistair Francis <alistair.francis@xxxxxxxxxx>
    Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
    Cc: Peter Maydell <peter.maydell@xxxxxxxxxx>
    Cc: qemu-devel@xxxxxxxxxx
    Fixes: 3e76099aacb4dae0d37ebf95305369e03d1491e6
    Signed-off-by: Laszlo Ersek <lersek@xxxxxxxxxx>
    Reviewed-by: Alistair Francis <alistair.francis@xxxxxxxxxx>
    Reviewed-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
    Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
 hw/core/loader.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/core/loader.c b/hw/core/loader.c
index c0d645a..4574249 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);
 }
 
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#master

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