linux-kernel - Re: [PATCH v4 14/27] x86/percpu: Adapt percpu for PIE support

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Message-ID: <01000163ae145cac-5ac07b51-8f08-4da5-bb93-0238d59756d3-000000@email.amazonses.com>
Date:   Tue, 29 May 2018 22:46:00 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     Thomas Garnier <thgarnie@...gle.com>
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Subject: Re: [PATCH v4 14/27] x86/percpu: Adapt percpu for PIE support

On Tue, 29 May 2018, Thomas Garnier wrote:

> Perpcu uses a clever design where the .percu ELF section has a virtual
> address of zero and the relocation code avoid relocating specific
> symbols. It makes the code simple and easily adaptable with or without
> SMP support.
>
> This design is incompatible with PIE because generated code always try to
> access the zero virtual address relative to the default mapping address.

We always access relative to the "segment register".

You can already change the segment register to relocate the per cpu
sections arbitrarily since all per cpu "addresses" are offsets relative to
the segment register. I am not sure what exactly you are trying to
accomplish here?

Maybe you need to explain it better?