Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933972AbaD3Q2t (ORCPT ); Wed, 30 Apr 2014 12:28:49 -0400 Received: from mail-ob0-f180.google.com ([209.85.214.180]:36687 "EHLO mail-ob0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933742AbaD3Q2r (ORCPT ); Wed, 30 Apr 2014 12:28:47 -0400 MIME-Version: 1.0 In-Reply-To: <201404301335.s3UDZX4J017978@glazunov.sibelius.xs4all.nl> References: <53554846.3070608@zytor.com> <53608125.2020103@zytor.com> <536085B7.5070002@zytor.com> <201404301335.s3UDZX4J017978@glazunov.sibelius.xs4all.nl> From: Hui Zhu Date: Thu, 1 May 2014 00:28:07 +0800 Message-ID: Subject: Re: [PATCH] Fix get ERESTARTSYS with m32 in x86_64 when debug by GDB To: Mark Kettenis Cc: "H. Peter Anvin" , pinskia@gmail.com, Thomas Gleixner , Ingo Molnar , x86@kernel.org, eparis@redhat.com, ak@linux.intel.com, "linux-kernel@vger.kernel.org" , "gdb@sourceware.org" , Pedro Alves Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 30, 2014 at 9:35 PM, Mark Kettenis wrote: >> Date: Tue, 29 Apr 2014 22:10:15 -0700 >> From: "H. Peter Anvin" >> >> On 04/29/2014 10:08 PM, Andrew Pinski wrote: >> > >> > restoring the values is hard since even the ptrace interface does not >> > allow for that. >> > >> >> So that begs the ultimate question, which is: given the fact that there >> is *state missing* from the state vector (this is the core of the >> problem), is there a way we can add that state so that gdb will be able >> to save and restore it? > > Carrying around additional state in GDB is complicated; I'd rather > avoid it. > > arch/x86/kernel/ptrace.c:putreg32() has this bit of code: > > case offsetof(struct user32, regs.orig_eax): > /* > * A 32-bit debugger setting orig_eax means to restore > * the state of the task restarting a 32-bit syscall. > * Make sure we interpret the -ERESTART* codes correctly > * in case the task is not actually still sitting at the > * exit from a 32-bit syscall with TS_COMPAT still set. > */ > regs->orig_ax = value; > if (syscall_get_nr(child, regs) >= 0) > task_thread_info(child)->status |= TS_COMPAT; > break; > > which gets used for 32-bit compat ptrace(2). Perhaps the same logic > should be added to putreg() if the child is a 32-bit process? Make a new patch that add following code to putreg(): case offsetof(struct user_regs_struct, orig_ax): /* * A 64-bit debugger setting orig_ax of a 32-bit inferior * means to restore the state of the task restarting a * 32-bit syscall. * Make sure we interpret the -ERESTART* codes correctly * in case the task is not actually still sitting at the * exit from a 32-bit syscall with TS_COMPAT still set. */ if (test_ti_thread_flag(task_thread_info(child), TIF_IA32)) { struct pt_regs *regs = task_pt_regs(child); regs->orig_ax = value; if (syscall_get_nr(child, regs) >= 0) task_thread_info(child)->status |= TS_COMPAT; return 0; } > > If (and only if) the goal of that TS_COMPAT flag solely is to trigger > the error code sign-extension in arch/x86/asm/syscall.h:syscall_get_error(), > we could work around to problem in GDB by checking "orig_ax" to see if > we're continuing an interrupted system call and sign extend the error > code in the real "eax" register if we are. I will update patch in https://sourceware.org/ml/gdb-patches/2014-04/msg00429.html according to this comments. Thanks, Hui Signed-off-by: Hui Zhu --- --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -452,6 +452,23 @@ static int putreg(struct task_struct *ch if (child->thread.gs != value) return do_arch_prctl(child, ARCH_SET_GS, value); return 0; + case offsetof(struct user_regs_struct, orig_ax): + /* + * A 64-bit debugger setting orig_ax of a 32-bit inferior + * means to restore the state of the task restarting a + * 32-bit syscall. + * Make sure we interpret the -ERESTART* codes correctly + * in case the task is not actually still sitting at the + * exit from a 32-bit syscall with TS_COMPAT still set. + */ + if (test_ti_thread_flag(task_thread_info(child), TIF_IA32)) { + struct pt_regs *regs = task_pt_regs(child); + regs->orig_ax = value; + if (syscall_get_nr(child, regs) >= 0) + task_thread_info(child)->status |= TS_COMPAT; + return 0; + } + break; #endif } -- 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/