linux-kernel - Re: [PATCH 0/3] Add __ioread32

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Message-Id: <20150915195031.0a1756a2.akpm@linux-foundation.org>
Date:	Tue, 15 Sep 2015 19:50:31 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Stephen Boyd <sboyd@...eaurora.org>,
	Andy Gross <agross@...eaurora.org>,
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-soc@...r.kernel.org,
	linux-mips@...ux-mips.org, Hauke Mehrtens <hauke@...ke-m.de>,
	Paul Walmsley <paul@...an.com>,
	Rafał Miłecki <zajec5@...il.com>,
	Bjorn Andersson <bjorn.andersson@...ymobile.com>
Subject: Re: [PATCH 0/3] Add __ioread32_copy() and use it

On Wed, 16 Sep 2015 04:32:19 +0200 Andi Kleen <andi@...stfloor.org> wrote:

> > __iowrite32_copy() is marked __visible.  I don't actually know what
> > that does and Andi's d47d5c8194579bc changelog (which sucks the big
> > one) didn't explain it.  Apparently it has something to do with being
> > implemented in assembly, but zillions of functions are implemented in
> > assembly, so why are only two functions marked this way?  Anyway,
> > __ioread32_copy() is implemented in C so I guess __visible isn't needed
> > there.
> 
> __visible is needed for C functions that are called from assembler.
> Otherwise the compiler may optimize them away.

Under what circumstances will the compiler (or linker?) do this? 
LTO enabled?

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