From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39170) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cBnL1-000622-L1 for qemu-devel@nongnu.org; Tue, 29 Nov 2016 13:41:08 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cBnKw-00019C-Ii for qemu-devel@nongnu.org; Tue, 29 Nov 2016 13:41:07 -0500 Received: from mx1.redhat.com ([209.132.183.28]:33758) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cBnKw-00017V-9s for qemu-devel@nongnu.org; Tue, 29 Nov 2016 13:41:02 -0500 References: <20161128195701.24912-1-lersek@redhat.com> <20161128195701.24912-3-lersek@redhat.com> <20161129182831-mutt-send-email-mst@kernel.org> From: Laszlo Ersek Message-ID: <964fe6d4-37e5-b77b-f22e-ad09784a7de3@redhat.com> Date: Tue, 29 Nov 2016 19:40:58 +0100 MIME-Version: 1.0 In-Reply-To: <20161129182831-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit 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: "Michael S. Tsirkin" Cc: qemu devel list , Alistair Francis , Paolo Bonzini , Peter Maydell On 11/29/16 17:29, Michael S. Tsirkin wrote: > 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. Just to comply with the word of the standard above; it says "any valid pointer to void". > >> -- >> 2.9.2