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Date: Mon, 26 Oct 2020 09:08:38 -0700 From: Kyle Huey <me@...ehuey.com> To: Peter Zijlstra <peterz@...radead.org> Cc: open list <linux-kernel@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, "Robert O'Callahan" <rocallahan@...il.com>, Alexandre Chartre <alexandre.chartre@...cle.com>, "Paul E. McKenney" <paulmck@...nel.org>, Frederic Weisbecker <frederic@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <sean.j.christopherson@...el.com>, Masami Hiramatsu <mhiramat@...nel.org>, Petr Mladek <pmladek@...e.com>, Joel Fernandes <joel@...lfernandes.org>, Steven Rostedt <rostedt@...dmis.org>, Boris Ostrovsky <boris.ostrovsky@...cle.com>, Juergen Gross <jgross@...e.com>, Brian Gerst <brgerst@...il.com>, Andy Lutomirski <luto@...nel.org>, Josh Poimboeuf <jpoimboe@...hat.com>, Daniel Thompson <daniel.thompson@...aro.org> Subject: Re: [REGRESSION] x86/debug: After PTRACE_SINGLESTEP DR_STEP is no longer reported in dr6 On Mon, Oct 26, 2020 at 8:55 AM Peter Zijlstra <peterz@...radead.org> wrote: > Urgh, now I have to try and remember how all that worked again ... Sorry. > I suspect it's either one (or both) of the last two: > > f4956cf83ed1 ("x86/debug: Support negative polarity DR6 bits") > d53d9bc0cf78 ("x86/debug: Change thread.debugreg6 to thread.virtual_dr6") I think it's the latter, particularly the removal of this assignment[0] > Just to clarify, the sequence is something like: > > - tracer: ptrace(PTRACE_SINGLESTEP) > - tracee: #DB, DR6 contains DR_STEP > - tracer: ptrace_get_debugreg(6) Right. > Also, can you confirm that pthread_set_debugreg(6) should not do > anything useful? I don't believe it did anything useful. - Kyle [0] https://github.com/torvalds/linux/commit/d53d9bc0cf78#diff-51ce909c2f65ed9cc668bc36cc3c18528541d8a10e84287874cd37a5918abae5L790
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