linux-kernel - Re: [PATCH 5/5] arm64: Add uprobe support

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Message-ID: <20160809184943.GA17112@redhat.com>
Date:	Tue, 9 Aug 2016 20:49:44 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Pratyush Anand <panand@...hat.com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux@....linux.org.uk,
	catalin.marinas@....com, will.deacon@....com,
	linux-kernel@...r.kernel.org, wcohen@...hat.com,
	dave.long@...aro.org, steve.capper@...aro.org,
	srikar@...ux.vnet.ibm.com, vijaya.kumar@...iumnetworks.com,
	Shi Yang <yang.shi@...aro.org>,
	Andre Przywara <andre.przywara@....com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Ashok Kumar <ashoks@...adcom.com>,
	James Morse <james.morse@....com>,
	Jungseok Lee <jungseoklee85@...il.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Mark Rutland <mark.rutland@....com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Robin Murphy <robin.murphy@....com>,
	Sandeepa Prabhu <sandeepa.s.prabhu@...il.com>,
	Shaokun Zhang <zhangshaokun@...ilicon.com>,
	"Suzuki K. Poulose" <suzuki.poulose@....com>,
	Vladimir Murzin <vladimir.murzin@....com>
Subject: Re: [PATCH 5/5] arm64: Add uprobe support

On 08/02, Pratyush Anand wrote:
>
> This patch adds support for uprobe on ARM64 architecture.

I know nothing about ARM, so I can't actually review this change.
But it looks good to me ;)

Just one note,

> +int arch_uprobe_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
> +{
> +	struct uprobe_task *utask = current->utask;
> +
> +	/* saved fault code is restored in post_xol */
> +	utask->autask.saved_fault_code = current->thread.fault_code;
> +
> +	/* An invalid fault code between pre/post xol event */
> +	current->thread.fault_code = UPROBE_INV_FAULT_CODE;
> +
> +	/* Instruction point to execute ol */
> +	instruction_pointer_set(regs, utask->xol_vaddr);
> +
> +	user_enable_single_step(current);

I don't think we want user_{enable,disable{_single_step in the long term,
please look at 9bd1190a11c9d2 "uprobes/x86: Do not (ab)use TIF_SINGLESTEP
/user_*_single_step() for single-stepping". it seems that ARM64 sets/clears
TIF_SINGLESTEP. You can also lool at saved_tf logic, probably ARM64 needs
the same.

However, I agree we can do this later and initial version can use these
ptrace helpers.

Oleg.