From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:54220) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Rv4DQ-0004EO-QB for qemu-devel@nongnu.org; Wed, 08 Feb 2012 04:53:32 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Rv4DE-00033j-6Y for qemu-devel@nongnu.org; Wed, 08 Feb 2012 04:53:28 -0500 Received: from fmmailgate03.web.de ([217.72.192.234]:51747) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Rv4DD-00033J-Tq for qemu-devel@nongnu.org; Wed, 08 Feb 2012 04:53:16 -0500 Received: from moweb002.kundenserver.de (moweb002.kundenserver.de [172.19.20.108]) by fmmailgate03.web.de (Postfix) with ESMTP id D86521B0B1914 for ; Wed, 8 Feb 2012 10:53:13 +0100 (CET) From: Goswin von Brederlow References: Date: Wed, 08 Feb 2012 10:53:12 +0100 In-Reply-To: (Stefan Hajnoczi's message of "Mon, 6 Feb 2012 12:38:14 +0000") Message-ID: <87y5sdejnb.fsf@frosties.localnet> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] Support for multiboot images in elf64 (EM_X86_64) format List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: qemu-devel@nongnu.org, Goswin von Brederlow Stefan Hajnoczi writes: > On Sat, Feb 4, 2012 at 5:38 PM, Goswin von Brederlow wrote: >> Description: Allow 64bit elf binaries in multiboot format >> =A0This patch allows 64bit elf files with multiboot header to be loade= d. >> =A0The entry point will still be called in 32bit mode and the kernel >> =A0must switch to 64bit mode on its own. The image and all modules mus= t >> =A0also be located in the lower 2GB of ram. All the restrictions of a >> =A032bit image still apply. >> Author: Goswin von Brederlow >> Last-Updated: 2011-04-08 >> --- > > The multiboot specification is 32-bit only. This patch enables a > non-standard 64-bit version of multiboot. Have you checked whether > GRUB or other multiboot loaders have equivalent functionality? Have > you contacted the multiboot specification authors? Not really. The multiboot specification allow for different executable formats as long as the multiboot header is correct. For example you can have an a.out multiboot image. The entry vector specified in the multiboot header is still called in 32bit mode, as per specs. All that changes is that the kvm allows another executable format for loading the image. Actually per mutliboot specs the elf64 image should already be loaded as plain image (which means not neccessarily reloacted to the right address) just like a.out would but kvm doesn't support that. I don't think other loaders support elf64 (yet) unless they support plain images. Frankly I never tried booting a toy kernel on real hardware so there never was the need. >> --- qemu-kvm-0.14.0+dfsg.orig/hw/multiboot.c >> +++ qemu-kvm-0.14.0+dfsg/hw/multiboot.c >> @@ -173,8 +173,7 @@ int load_multiboot(void *fw_cfg, >> =A0 =A0 =A0 =A0 fclose(f); >> >> =A0 =A0 =A0 =A0 if (((struct elf64_hdr*)header)->e_machine =3D=3D EM_X= 86_64) { >> - =A0 =A0 =A0 =A0 =A0 =A0fprintf(stderr, "Cannot load x86-64 image, gi= ve a 32bit one.\n"); >> - =A0 =A0 =A0 =A0 =A0 =A0exit(1); >> + =A0 =A0 =A0 =A0 =A0 mb_debug("qemu: 64bit elf, I hope you know what = you are doing\n"); > > This is silent by default, but given the nature of 64-bit multiboot > support I think this warning should be on by default. Anyone using > this really needs to know what they are doing and QEMU should not > silently do weird things. > > Stefan Fine by me to make this more verbose. I only care about removing the exit(1). MfG Goswin