Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753756AbbB0LVl (ORCPT ); Fri, 27 Feb 2015 06:21:41 -0500 Received: from mail-wg0-f48.google.com ([74.125.82.48]:38178 "EHLO mail-wg0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752788AbbB0LVh (ORCPT ); Fri, 27 Feb 2015 06:21:37 -0500 Message-ID: <54F052B1.4070300@vanguardiasur.com.ar> Date: Fri, 27 Feb 2015 08:19:13 -0300 From: Ezequiel Garcia Organization: VanguardiaSur User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Chung-Lin Tang , Arnd Bergmann CC: Tobias Klauser , Walter Goossens , Ley Foon Tan , linux-arch@vger.kernel.org, "nios2-dev@lists.rocketboards.org" , "linux-kernel@vger.kernel.org" Subject: Re: nios2: is the ptrace ABI correct? References: <10088870.tldQegtTla@wuerfel> <54EDB2FC.4050901@vanguardiasur.com.ar> <10841724.NbdcAaCe1a@wuerfel> <54F03184.7080600@codesourcery.com> In-Reply-To: <54F03184.7080600@codesourcery.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3585 Lines: 98 Hi Chung-Lin Tang, On 02/27/2015 05:57 AM, Chung-Lin Tang wrote: > On 15/2/25 10:07 PM, Arnd Bergmann wrote: >> On Wednesday 25 February 2015 08:33:16 Ezequiel Garcia wrote: >>> >>> /me is more confused now >>> >>> In arch/nios2/include/asm/ucontext.h >>> >>> struct ucontext { >>> unsigned long uc_flags; >>> struct ucontext *uc_link; >>> stack_t uc_stack; >>> struct mcontext uc_mcontext; >>> sigset_t uc_sigmask; >>> }; >>> >>> And in include/uapi/asm-generic/ucontext.h: >>> >>> struct ucontext { >>> unsigned long uc_flags; >>> struct ucontext *uc_link; >>> stack_t uc_stack; >>> struct sigcontext uc_mcontext; >>> sigset_t uc_sigmask; >>> }; >>> >>> Which one is the one that userspace sees? And why does the kernel has >>> two different structures? >> >> Userspace sees the asm-generic header, which I assume is a bug >> in this case. > > Yes, I believe nios2 doesn't not need this asm-generic/ucontext.h > header; OTOH it just isn't used; no real harm done, so easily fixed. > >>> Given this oddities, I'm wondering how troublesome would be to just >>> re-do this and break the ptrace and signal ABI. For instance, just >>> pushing pt_regs in PTRACE_GETREGSET would make things much clearer. >> >> Could you change pt_regs to match the layout you have for PTRACE_GETREGSET >> instead? It seems much more intuitive. > > There is a reason for this pt_regs arrangement: the nios2 syscall > interface uses r4-r9 for parameters, while the usual C conventions use > only r4-r7, placing r8-r9 at the start of pt_regs creates a natural > stack layout for entering C code after the asm shims in entry.S > >>> I guess Linus would burn me for even suggesting to breaking users... but >>> do we have any users at all? This arch has just been mainlined. Altera's >>> out-of-tree is already ABI-incompatible with mainline so that's not an >>> issue. >>> >>> The only one using this ABI is gdb, which is easily fixed. >> >> You can change anything you like as long as nobody complains about >> regressions. > > PTRACE_GET/SETREGSET is a new feature in nios2-linux that we're still > about to support in upstream GDB, so things could be fixed if needed, > but why can't you just use the [0...] ordering in userspace? > Sure, that's doable. However, I believe the problem is the pt_regs struct is exported in ptrace.h so we seem to be telling userspace to use it. > BTW, it's even that way in signal stacks as well; nios2 does not > use/export sigcontext inside struct ucontext. We just use a int[32] > array there. > I think we are more or less on the same page. Right now, my biggest problem is how to remove the pt_regs from being exported to userspace, without breaking things. The struct is defined and used in a few UAPI headers: arch/nios2/include/uapi/asm/ptrace.h arch/nios2/include/uapi/asm/sigcontext.h arch/nios2/include/uapi/asm/elf.h For ucontext, we would need to remove arch/nios2/include/uapi/asm/sigcontext.h and avoid using asm-generic/ucontext.h. For ptrace, we could move pt_regs from the UAPI header to some internal header. That way userspace is not exposed the wrong struct. For the elf coredump, I have no idea yet :) -- Ezequiel Garcia, VanguardiaSur www.vanguardiasur.com.ar -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/