From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1MnWCw-0002Lz-Ip for qemu-devel@nongnu.org; Tue, 15 Sep 2009 07:28:26 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1MnWCr-0002JV-BV for qemu-devel@nongnu.org; Tue, 15 Sep 2009 07:28:25 -0400 Received: from [199.232.76.173] (port=58009 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1MnWCr-0002JI-2N for qemu-devel@nongnu.org; Tue, 15 Sep 2009 07:28:21 -0400 Received: from mail.gmx.net ([213.165.64.20]:50937) by monty-python.gnu.org with smtp (Exim 4.60) (envelope-from ) id 1MnWCp-0000dd-TN for qemu-devel@nongnu.org; Tue, 15 Sep 2009 07:28:20 -0400 Content-Type: text/plain; charset="iso-8859-1" Date: Tue, 15 Sep 2009 13:28:16 +0200 From: "Johannes Luber" In-Reply-To: Message-ID: <20090915112816.99190@gmx.net> MIME-Version: 1.0 References: <20090914090001.99230@gmx.net> Subject: Re: [Qemu-devel] tlb_update_dirty() question Content-Transfer-Encoding: 8bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Blue Swirl Cc: qemu-devel@nongnu.org > On Mon, Sep 14, 2009 at 12:00 PM, Johannes Luber wrote: ... > > > > The comment is particularly insightful. p is supposed to be a host > pointer yet the initialization code uses "(unsigned long)" in a cast for an > expression which has the type target_phys_addr_t because the struct variable > "addend" has this type. > > The addend is target_phys_addr_t type, because then we can get back to > host address ranges on 32 bit host. Consider for example guest address > at 8G backed by host memory at 1G: the addend is -7G. Looking at int tlb_set_page_exec(CPUState *env, target_ulong vaddr, target_phys_addr_t paddr, int prot, int mmu_idx, int is_softmmu) { } (I assume that the only place addend is set), I see these two lines: addend = (unsigned long)qemu_get_ram_ptr(pd & TARGET_PAGE_MASK); ... te->addend = addend - vaddr; Assuming target_ulong and unsigned long as 32-bit values (despite being on 64-bit system) I don't see how your example can work. There is no way to make addend bigger than (+/-)4G. > > > This cast assumes that unsigned long is at least as big as > target_phys_addr_t. Under Unix this may be true, but Windows C compilers treat long == > int and int remains a 32-bit type. Why isn't simply target_phys_addr_t used > as cast? target_phys_addr_t does support max(target pointer size, host > pointer size), doesn't it? Or is there another option? > > No, the cast assumes that sum of guest addr and addend is a valid host > address, which should be true. For memory, the resulting address is > simply pointer to host memory. If any of the lowest bits of the sum > are set, the area is MMIO. > All in all, I take it that Qemu basically targets only Unix (the link to the Windows source version is merely a patch set). At least I know that my assumptions have been right and so I can fix these "(unsigned long)" places for myself. Thanks for your time! Johannes -- GRATIS für alle GMX-Mitglieder: Die maxdome Movie-FLAT! Jetzt freischalten unter http://portal.gmx.net/de/go/maxdome01