From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58999) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cBV7Z-00011D-Ii for qemu-devel@nongnu.org; Mon, 28 Nov 2016 18:14:05 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cBV7U-0004jb-3l for qemu-devel@nongnu.org; Mon, 28 Nov 2016 18:13:57 -0500 Received: from mail-oi0-x242.google.com ([2607:f8b0:4003:c06::242]:35457) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1cBV7T-0004jR-Uy for qemu-devel@nongnu.org; Mon, 28 Nov 2016 18:13:56 -0500 Received: by mail-oi0-x242.google.com with SMTP id v84so15944417oie.2 for ; Mon, 28 Nov 2016 15:13:55 -0800 (PST) MIME-Version: 1.0 Sender: alistair23@gmail.com In-Reply-To: <20161128195701.24912-3-lersek@redhat.com> References: <20161128195701.24912-1-lersek@redhat.com> <20161128195701.24912-3-lersek@redhat.com> From: Alistair Francis Date: Mon, 28 Nov 2016 15:13:24 -0800 Message-ID: Content-Type: text/plain; charset=UTF-8 Subject: Re: [Qemu-devel] [PATCH for-2.8 2/2] loader: fix undefined behavior in rom_order_compare() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Laszlo Ersek Cc: qemu devel list , Peter Maydell , Paolo Bonzini , Alistair Francis , "Michael S. Tsirkin" On Mon, Nov 28, 2016 at 11:57 AM, Laszlo Ersek wrote: > 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" > Cc: Alistair Francis > Cc: Paolo Bonzini > Cc: Peter Maydell > Cc: qemu-devel@nongnu.org > Fixes: 3e76099aacb4dae0d37ebf95305369e03d1491e6 > Signed-off-by: Laszlo Ersek Reviewed-by: Alistair Francis Thanks, Alistair > --- > 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 c0d645a87134..766e48f2aec2 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); > } > > -- > 2.9.2 > >