From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51061) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cBlHL-00011X-As for qemu-devel@nongnu.org; Tue, 29 Nov 2016 11:29:12 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cBlHI-0004R7-6w for qemu-devel@nongnu.org; Tue, 29 Nov 2016 11:29:11 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40143) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cBlHH-0004QX-Ub for qemu-devel@nongnu.org; Tue, 29 Nov 2016 11:29:08 -0500 Date: Tue, 29 Nov 2016 18:29:05 +0200 From: "Michael S. Tsirkin" Message-ID: <20161129182831-mutt-send-email-mst@kernel.org> References: <20161128195701.24912-1-lersek@redhat.com> <20161128195701.24912-3-lersek@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161128195701.24912-3-lersek@redhat.com> 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 , Alistair Francis , Paolo Bonzini , Peter Maydell On Mon, Nov 28, 2016 at 08:57:01PM +0100, 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 > --- > 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); > } Can't hurt but why cast to void *? Should not be needed. > -- > 2.9.2