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

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Message-ID: <20091218005650.GA20667@redhat.com>
Date:	Fri, 18 Dec 2009 01:56:50 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	"K.Prasad" <prasad@...ux.vnet.ibm.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>, Roland McGrath <roland@...hat.com>
Cc:	linux-kernel@...r.kernel.org, utrace-devel@...hat.com
Subject: x86: do_debug && PTRACE_SINGLESTEP broken by
	08d68323d1f0c34452e614263b212ca556dae47f

Hi.

do_debug() is obviously wrong wrt PTRACE_SINGLESTEP/TIF_SINGLESTEP, no?

Afaics this was broken by

	hw-breakpoints: modifying generic debug exception to use thread-specific debug registers
	commit 08d68323d1f0c34452e614263b212ca556dae47f

To verify, the "patch" below fixes the stepping for me, not sure what
is the proper fix...

Oleg.

--- arch/x86/kernel/traps.c~	2009-12-18 00:20:49.000000000 +0100
+++ arch/x86/kernel/traps.c	2009-12-18 01:44:05.000000000 +0100
@@ -575,7 +575,7 @@ dotraplinkage void __kprobes do_debug(st
 		regs->flags &= ~X86_EFLAGS_TF;
 	}
 	si_code = get_si_code(tsk->thread.debugreg6);
-	if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS))
+//	if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS))
 		send_sigtrap(tsk, regs, error_code, si_code);
 	preempt_conditional_cli(regs);
 

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