linux-kernel - Re: [PATCH] x86: make PTRACE_GETREGSET return 32-bit regs if 64-bit process entered kernel with int 80

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Date:	Fri, 15 Feb 2013 16:09:40 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Andi Kleen <andi@...stfloor.org>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: Re: [PATCH] x86: make PTRACE_GETREGSET return 32-bit regs if
	64-bit process entered kernel with int 80

On 02/15, Cyrill Gorcunov wrote:
>
> > strace needs to get that data on every syscall entry in the traced process.
> > Doing open/read/close on every syscall entry is going to slow it down a lot.
>
> Don't you need to read it only once when strace is attached? Compat flag can't
> be arbitrary dropped when program executes, no?

TS_COMPAT is set/cleared every time a 64bit task does int80.

I guess you need TIF_IA32, not TS_COMPAT, for c/r.

Oleg.

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