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Date: Thu, 8 Mar 2012 14:48:09 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Peter Zijlstra <peterz@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
        Christoph Hellwig <hch@infradead.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Anton Arapov <anton@redhat.com>,
        Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
        Jim Keniston <jkenisto@linux.vnet.ibm.com>,
        Jiri Olsa <jolsa@redhat.com>, Josh Stone <jistone@redhat.com>
Subject: Re: [PATCH] uprobes/core: handle breakpoint and signal step
 exception.
Message-ID: <20120308134809.GB28488@elte.hu>
References: <20120223110245.12459.7391.sendpatchset@srdronam.in.ibm.com>
 <20120227091212.GA7092@elte.hu>
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* Srikar Dronamraju <srikar@linux.vnet.ibm.com> wrote:

> @@ -233,9 +233,11 @@ static inline void __user *arch_compat_alloc_user_space(long len)
>  
>  	if (test_thread_flag(TIF_IA32)) {
>  		sp = task_pt_regs(current)->sp;
> +#ifdef CONFIG_X86_64
>  	} else {
>  		/* -128 for the x32 ABI redzone */
>  		sp = __this_cpu_read(old_rsp) - 128;
> +#endif
>  	}
>  
>  	return (void __user *)round_down(sp - len, 16);

So 'sp' is undefined if that TIF check fails?

Also, on a 32-bit kernel the TIF check probably fails all the 
time, because we don't set TIF_IA32 (and don't know that flag).

It would probably be better to make the whole helper inline 
#ifdef 64-bit, it does not look very useful on 32-bit.

Thanks,

	Ingo