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Date:   Fri, 26 Feb 2021 09:47:25 -0800
From:   Sean Christopherson <seanjc@google.com>
To:     Nadav Amit <nadav.amit@gmail.com>
Cc:     Linux-MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
        Hugh Dickins <hughd@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Andrew Morton <akpm@linux-foundation.org>, x86@kernel.org
Subject: Re: [RFC 1/6] vdso/extable: fix calculation of base
Message-ID: <YDk0Ld5TIEnhA0Cb@google.com>
References: <20210225072910.2811795-1-namit@vmware.com>
 <20210225072910.2811795-2-namit@vmware.com>
 <YDgTrqNDk+vPF9LA@google.com>
 <2CDFE432-90D3-43EE-BA9F-2CFEB8BB343C@gmail.com>
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On Fri, Feb 26, 2021, Nadav Amit wrote:
> 
> > On Feb 25, 2021, at 1:16 PM, Sean Christopherson <seanjc@google.com> wrote:
> > It's been literally years since I wrote this code, but I distinctly remember the
> > addresses being relative to the base.  I also remember testing multiple entries,
> > but again, that was a long time ago.
> > 
> > Assuming things have changed, or I was flat out wrong, the comment above the
> > macro magic should also be updated.
> > 
> > /*
> > * Inject exception fixup for vDSO code.  Unlike normal exception fixup,
> > * vDSO uses a dedicated handler the addresses are relative to the overall
> > * exception table, not each individual entry.
> > */
> 
> I will update the comment. I am not very familiar with pushsection stuff,
> but the offsets were wrong.
> 
> Since you say you checked it, I wonder whether it can somehow be caused
> by having exception table entries defined from multiple object files.

Oooh, I think that would do it.  Have you checked what happens if there are
multiple object files and multiple fixups within an object file?

> Anyhow, this change follows the kernel’s (not vDSO) exception table
> scheme.