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Date: Wed, 24 Aug 2016 17:47:11 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Pratyush Anand <panand@redhat.com>
Cc: linux-arm-kernel@lists.infradead.org, linux@arm.linux.org.uk,
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Subject: Re: [PATCH 5/5] arm64: Add uprobe support
Message-ID: <20160824154711.GA25531@redhat.com>
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Hi Pratyush,

On 08/24, Pratyush Anand wrote:
>
> > 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.
>
> IIUC, then you mean that TIF_SINGLESTEP is a per task flag,

Yes, and nobody but ptrace should use it, otherwise ptrace/uprobes can confuse
each other. And uprobes simply doesn't need to set/clear it.

> while
> arch_uprobe_pre/post_xol() should enable/disable single stepping using a per
> uprobe_task,

I can't really answer since I know nothing about arm. x86 just needs to set
X86_EFLAGS_TF, I guess arm needs to modify some register too?

> and we should have a flag in "struct arch_uprobe_task" to handle
> this, right?

Probably yes, because we need to record/restore X86_EFLAGS_TF in case it
was already set by ptrace or something else.

> > However, I agree we can do this later and initial version can use these
> > ptrace helpers.
>
> Yes, I would also like to do that change latter, because these set of patches
> have already been tested heavily with systemtap, so it would be better to go
> with an incremental changes latter on.

Yes, yes, I agree. Let me repeat that this patch looks good to me as initial
version, but obviously I can't really revit it and/or ack.

Oleg.