Re: [PATCH 07/10] uprobes/x86: Introduce arch_uretprobe_is_alive()

From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
	Anton Arapov <arapov@gmail.com>,
	David Long <dave.long@linaro.org>,
	Denys Vlasenko <dvlasenk@redhat.com>,
	"Frank Ch. Eigler" <fche@redhat.com>,
	Ingo Molnar <mingo@kernel.org>, Jan Willeke <willeke@de.ibm.com>,
	Jim Keniston <jkenisto@us.ibm.com>,
	Mark Wielaard <mjw@redhat.com>,
	Pratyush Anand <panand@redhat.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 07/10] uprobes/x86: Introduce arch_uretprobe_is_alive()
Date: Thu, 7 May 2015 16:38:52 +0530	[thread overview]
Message-ID: <20150507110852.GF30396@linux.vnet.ibm.com> (raw)
In-Reply-To: <20150504124914.GA22512@redhat.com>

> 
> diff --git a/arch/x86/include/asm/uprobes.h b/arch/x86/include/asm/uprobes.h
> index f011fd0..60777f3 100644
> --- a/arch/x86/include/asm/uprobes.h
> +++ b/arch/x86/include/asm/uprobes.h
> @@ -57,6 +57,7 @@ struct arch_uprobe {
>  };
> 
>  struct arch_uretprobe {
> +	unsigned long	sp;

While this looks good, I was wondering if you did think of having the sp
in the return_instance structure itself. I mean can we use
user_stack_pointer() to populate the ri->sp?
In which case the weak function itself should suffice for most archs.

Something like this.
prepare_uretprobe() we can have
ri->sp = user_stack_pointer(regs)

and handle_trampoline() would call something like 

	arch_uretprobe_is_alive(next->sp, regs);

bool __weak arch_uretprobe_is_alive(unsigned long sp, struct pt_regs *regs)
{
	return user_stack_pointer(regs) <= sp;
}

Am I missing something?

> 
-- 
Thanks and Regards
Srikar Dronamraju