linux-kernel - Re: x86: do_debug && PTRACE_SINGLESTEP broken by 08d68323d1f0c34452e614263b212ca556dae47f

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Date:	Thu, 17 Dec 2009 17:40:21 -0800 (PST)
From:	Roland McGrath <roland@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	"K.Prasad" <prasad@...ux.vnet.ibm.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	utrace-devel@...hat.com
Subject: Re: x86: do_debug && PTRACE_SINGLESTEP broken by
	08d68323d1f0c34452e614263b212ca556dae47f

Comparing to the old (2.6.32) logic, I think it might be this (untested).
I also note this is the sole use of get_si_code, seems like it should
just be rolled in here.


Thanks,
Roland


diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 3339917..16a88f5 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -530,7 +530,6 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
 {
 	struct task_struct *tsk = current;
 	unsigned long dr6;
-	int si_code;
 
 	get_debugreg(dr6, 6);
 
@@ -569,14 +568,15 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
 	 * We already checked v86 mode above, so we can check for kernel mode
 	 * by just checking the CPL of CS.
 	 */
+	dr6 = tsk->thread.debugreg6;
 	if ((dr6 & DR_STEP) && !user_mode(regs)) {
 		tsk->thread.debugreg6 &= ~DR_STEP;
 		set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
 		regs->flags &= ~X86_EFLAGS_TF;
+	} else if (dr6 & (DR_STEP | DR_TRAP_BITS)) {
+		send_sigtrap(tsk, regs, error_code, get_si_code(dr6));
 	}
-	si_code = get_si_code(tsk->thread.debugreg6);
-	if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS))
-		send_sigtrap(tsk, regs, error_code, si_code);
+
 	preempt_conditional_cli(regs);
 
 	return;
--
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