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From: Roland McGrath <roland@redhat.com>
To: Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Subject: [PATCH] x86_64 ptrace orig_ax on ia32 task
Date: Fri,  7 Mar 2008 14:56:02 -0800 (PST)	[thread overview]
Message-ID: <20080307225602.6491B26F990@magilla.localdomain> (raw)
In-Reply-To: Roland McGrath's message of  Thursday, 28 February 2008 19:57:07 -0800 <20080229035707.EAE862700FD@magilla.localdomain>


This makes 64-bit ptrace calls setting the 64-bit orig_ax field
for a 32-bit task sign-extend the low 32 bits up to 64.  This
matches what a 64-bit debugger expects when tracing a 32-bit task.

This follows on my "x86_64 ia32 syscall restart fix".
This didn't matter until that was fixed.

The debugger ignores or zeros the high half of every register slot it
sets (including the orig_rax pseudo-register) uniformly.  It expects
that the setting of the low 32 bits always has the same meaning as a
32-bit debugger setting those same 32 bits with native 32-bit
facilities.

This never arose before because the syscall restart check never
matched any -ERESTART* values due to lack of sign extension.  Before
that fix, even 32-bit ptrace setting orig_eax to -1 failed to trigger
the restart check anyway.  So this was never noticed as a regression
of 64-bit debuggers vs 32-bit debuggers on the same 64-bit kernel.

Signed-off-by: Roland McGrath <roland@redhat.com>
---
 arch/x86/kernel/ptrace.c |   14 ++++++++++++++
 1 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index f8eed1b..92b44e1 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -322,6 +322,20 @@ static int putreg(struct task_struct *child,
 	case offsetof(struct user_regs_struct, flags):
 		return set_flags(child, value);
 
+#ifdef CONFIG_IA32_EMULATION
+	case offsetof(struct user_regs_struct, orig_ax):
+		/*
+		 * For a 32-bit task, setting only the low 32 bits and
+		 * leaving the high bits untouched (all 0) has the same
+		 * effect as setting those bits via 32-bit ptrace would.
+		 * This means sign-extending an orig_eax of -1, which
+		 * here is an orig_rax of (u32)-1.
+		 */
+		if (test_tsk_thread_flag(child, TIF_IA32))
+			value = (long) (s32) value;
+		break;
+#endif
+
 #ifdef CONFIG_X86_64
 	case offsetof(struct user_regs_struct,fs_base):
 		if (value >= TASK_SIZE_OF(child))

  parent reply	other threads:[~2008-03-07 22:57 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-29  3:57 [PATCH] x86_64 ia32 syscall restart fix Roland McGrath
2008-02-29 15:52 ` Ingo Molnar
2008-02-29 16:26   ` Linus Torvalds
2008-02-29 16:45     ` Ingo Molnar
2008-02-29 17:03       ` Linus Torvalds
2008-02-29 17:17         ` Ingo Molnar
2008-02-29 17:37           ` Ingo Molnar
2008-02-29 21:02             ` Andrew Morton
2008-02-29 21:20               ` Ingo Molnar
2008-03-01  5:48                 ` [stable] " Greg KH
2008-02-29 22:42     ` Roland McGrath
2008-02-29 23:18       ` Linus Torvalds
2008-03-07 22:56 ` Roland McGrath [this message]
2008-03-07 23:18   ` [PATCH] x86_64 ptrace orig_ax on ia32 task Linus Torvalds
2008-03-08  1:37     ` Roland McGrath
2008-03-10 19:19   ` Chuck Ebbert
2008-03-10 19:48     ` Linus Torvalds
2008-03-10 20:01       ` Roland McGrath
2008-03-11  9:32         ` Ingo Molnar

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