Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754694AbdDKLqX (ORCPT ); Tue, 11 Apr 2017 07:46:23 -0400 Received: from mga01.intel.com ([192.55.52.88]:16391 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752623AbdDKLqW (ORCPT ); Tue, 11 Apr 2017 07:46:22 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.37,185,1488873600"; d="scan'208";a="1154318282" Date: Tue, 11 Apr 2017 14:46:16 +0300 From: "Kirill A. Shutemov" To: Ingo Molnar , Andy Lutomirski Cc: "Kirill A. Shutemov" , Linus Torvalds , Andrew Morton , x86@kernel.org, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andi Kleen , Dave Hansen , linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/8] x86/boot/64: Add support of additional page table level during early boot Message-ID: <20170411114616.otx2f6aw5lcvfc2o@black.fi.intel.com> References: <20170406140106.78087-1-kirill.shutemov@linux.intel.com> <20170406140106.78087-4-kirill.shutemov@linux.intel.com> <20170411070203.GA14621@gmail.com> <20170411105106.4zgbzuu4s4267zyv@node.shutemov.name> <20170411112845.GA15212@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170411112845.GA15212@gmail.com> User-Agent: NeoMutt/20161126 (1.7.0) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2305 Lines: 57 On Tue, Apr 11, 2017 at 01:28:45PM +0200, Ingo Molnar wrote: > > * Kirill A. Shutemov wrote: > > > On Tue, Apr 11, 2017 at 09:02:03AM +0200, Ingo Molnar wrote: > > > I realize that you had difficulties converting this to C, but it's not going to > > > get any easier in the future either, with one more paging mode/level added! > > > > > > If you are stuck on where it breaks I'd suggest doing it gradually: first add a > > > trivial .c, build and link it in and call it separately. Then once that works, > > > move functionality from asm to C step by step and test it at every step. > > > > I've described the specific issue with converting this code to C in cover > > letter: how to make compiler to generate 32-bit code for a specific > > function or translation unit, without breaking linking afterwards (-m32 > > break it). > > Have you tried putting it into a separate .c file, and building it 32-bit? Yes, I have. The patch below fails linking: ld: i386 architecture of input file `arch/x86/boot/compressed/head64.o' is incompatible with i386:x86-64 output > > I think arch/x86/entry/vdso/Makefile contains an example of how to build 32-bit > code even on 64-bit kernels. I'll look closer (building proccess it's rather complicated), but my understanding is that VDSO is stand-alone binary and doesn't really links with the rest of the kernel, rather included as blob, no? Andy, may be you have an idea? diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index 44163e8c3868..8c1acacf408e 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -76,6 +76,8 @@ vmlinux-objs-$(CONFIG_EARLY_PRINTK) += $(obj)/early_serial_console.o vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/kaslr.o ifdef CONFIG_X86_64 vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/pagetable.o + vmlinux-objs-y += $(obj)/head64.o +$(obj)/head64.o: KBUILD_CFLAGS := -m32 -D__KERNEL__ -O2 endif $(obj)/eboot.o: KBUILD_CFLAGS += -fshort-wchar -mno-red-zone diff --git a/arch/x86/boot/compressed/head64.c b/arch/x86/boot/compressed/head64.c new file mode 100644 index 000000000000..42e1d64a15f4 --- /dev/null +++ b/arch/x86/boot/compressed/head64.c @@ -0,0 +1,3 @@ +void __startup32(void) +{ +} -- Kirill A. Shutemov