From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=60471 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PljIl-0000wm-2U for qemu-devel@nongnu.org; Sat, 05 Feb 2011 09:39:52 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PljIj-0000NM-N6 for qemu-devel@nongnu.org; Sat, 05 Feb 2011 09:39:50 -0500 Received: from moutng.kundenserver.de ([212.227.126.187]:56853) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PljIj-0000Mc-8F for qemu-devel@nongnu.org; Sat, 05 Feb 2011 09:39:49 -0500 Message-ID: <4D4D612F.2010904@mail.berlios.de> Date: Sat, 05 Feb 2011 15:39:43 +0100 From: Stefan Weil MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] Porting QEMU to new hosts with unusual ABI (sizeof(long) != sizeof(void *)) List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: QEMU Developers Cc: Blue Swirl , Anthony Liguori Currently, most QEMU code assumes that pointers and long integers have the same size, typically 32 bit on 32 bit hosts, 64 bit on 64 bit hosts. While this assumption works on QEMU's major hosts, it is not generally true. There exist 64 bit host OS which use an ABI with 32 bit long integers, maybe to be more compatible with an older 32 bit OS version, so here is sizeof(long) < sizeof(void *). Other ABIs might use "near" pointers which may reduce code size and improve code speed. This results in sizeof(long) > sizeof(void *). Both cases will break current QEMU, because lots of code lines use type casts from pointer to long or vice versa like these two examples: start = (long)mmap((void *)host_start, host_len ... code_gen_ptr = (void *)(((unsigned long)code_gen_ptr + ...)) Both variants (unsigned long) and (long) can be found (relation 3:2). Changing the existing limitation of QEMU's code simply needs replacing all those type casts, variable declarations and printf format specifiers by portable code. The standard integral type which matches the size of a pointer is defined in stdint.h (which also defines int8_t, ...). It is intptr_t (signed version) or uintptr_t (unsigned version). There is no need to use both. => Replace (unsigned long), (long) type casts of pointers by (uintptr_t). All variables (auto, struct members, parameters) which hold such values must be fixed, too. In the following examples, ptr_var is of that kind. => Replace unsigned long ptr_var, long ptr_var by uintptr_t ptr_var. Finally, the fixed variables are used in printf-like statements, so here the format specifier needs a change. inttypes.h defines PRIxPTR which should be used. => Replace "%lx" by "%" PRIxPTR to print the integer value ptr_var. A single patch which includes all these changes touches 39 files. Splitting it into smaller patches is not trivial because of cross dependencies. Because of its size, it will raise merge conflicts when it is not applied soon. Would these kind of changes be interesting for QEMU? Are there suggestions how it should be done? What about ram_addr_t? Should it be replaced by uintptr_t? Should we use macros like QEMU_PTR2UINT(p), QEMU_UINT2PTR(u)? My current version of the patch is available from http://qemu.weilnetz.de/0001-Fix-conversions-from-pointer-to-integral-type-and-vi.patch. Kind regards, Stefan Weil