linux-kernel - Re: [PATCH] parisc: prefer _THIS_IP_ and _RET_IP

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Date:   Fri, 3 Aug 2018 13:57:05 -0400
From:   John David Anglin <dave.anglin@...l.net>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     deller@....de, jejb@...isc-linux.org,
        Nathan Chancellor <natechancellor@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Pravin Shedge <pravin.shedge4linux@...il.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        linux-parisc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] parisc: prefer _THIS_IP_ and _RET_IP_ statement
 expressions

On 2018-08-02 4:31 PM, Nick Desaulniers wrote:
> If I understand your point correctly, is it that you're saying that
> _THIS_IP_  should be implemented in terms of inline assembly (as in
> what current_text_addr() is currently)?  If that's what you mean and
> I'm understanding correctly, my point is that we should be preferring
> the generic C implementation as that's what's being used in most
> places currently, so if it was broken you'd likely already know about
> it.  Unless unwinding is truly broken by the additional label, I don't
> think we need an inline assembly implementation of current_text_addr()
> for parisc (or any arch for that matter).  If we do, then it can be
> localized to the parisc unwinding code, that way it can be
> consolidated everywhere else for every other arch.
The label breaks the unwind data, not the unwind code.  So, localizing 
the use of
current_text_addr() to the parisc unwind code doesn't help.

Personally, I prefer the implementation of current_text_addr() because:

1) The generated code is smaller, and
2) it doesn't introduce any unnecessary labels into the text.

As noted, these labels can cause issues with unwinding.

Dave

-- 
John David Anglin  dave.anglin@...l.net