From: Andi Kleen <andi@firstfloor.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "Andi Kleen" <andi@firstfloor.org>,
"Stephen Boyd" <sboyd@codeaurora.org>,
"Andy Gross" <agross@codeaurora.org>,
linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, linux-soc@vger.kernel.org,
linux-mips@linux-mips.org, "Hauke Mehrtens" <hauke@hauke-m.de>,
"Paul Walmsley" <paul@pwsan.com>,
"Rafał Miłecki" <zajec5@gmail.com>,
"Bjorn Andersson" <bjorn.andersson@sonymobile.com>
Subject: Re: [PATCH 0/3] Add __ioread32_copy() and use it
Date: Sat, 19 Sep 2015 22:16:29 +0200 [thread overview]
Message-ID: <20150919201628.GI1747@two.firstfloor.org> (raw)
In-Reply-To: <20150918121919.fa20552946703ae772d636e9@linux-foundation.org>
On Fri, Sep 18, 2015 at 12:19:19PM -0700, Andrew Morton wrote:
> On Wed, 16 Sep 2015 04:55:46 +0200 Andi Kleen <andi@firstfloor.org> wrote:
>
> > > Under what circumstances will the compiler (or linker?) do this?
> >
> > Compiler.
> >
> > > LTO enabled?
> >
> > Yes it's for LTO. The optimization allows the compiler to drop unused
> > functions, which is very popular with users (a lot use it to get smaller
> > kernel images)
> >
>
> Does this look truthful and complete?
>
>
> --- a/include/linux/compiler-gcc.h~a
> +++ a/include/linux/compiler-gcc.h
> @@ -205,7 +205,10 @@
>
> #if GCC_VERSION >= 40600
> /*
> - * Tell the optimizer that something else uses this function or variable.
> + * When used with Link Time Optimization, gcc can optimize away C functions or
> + * variables which are referenced only from assembly code. __visible tells the
> + * optimizer that something else uses this function or variable, thus preventing
> + * this.
Yes,
In a few cases I also used it to work around LTO bugs in older gcc
releases. I don't think any of those fixes made it into mainline though,
and they are not needed anymore with 5.x
-Andi
prev parent reply other threads:[~2015-09-19 20:16 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-15 19:41 [PATCH 0/3] Add __ioread32_copy() and use it Stephen Boyd
2015-09-15 19:41 ` [PATCH 1/3] lib: iomap_copy: Add __ioread32_copy() Stephen Boyd
2015-09-15 19:41 ` [PATCH 2/3] soc: qcom: smd: Use __ioread32_copy() instead of open-coding it Stephen Boyd
2015-09-15 19:41 ` [PATCH 3/3] FIRMWARE: bcm47xx_nvram: Use __ioread32_copy() instead of open-coding Stephen Boyd
2015-09-15 22:58 ` [PATCH 0/3] Add __ioread32_copy() and use it Andrew Morton
2015-09-16 0:50 ` Stephen Boyd
2015-09-16 22:09 ` Andrew Morton
2015-09-16 2:32 ` Andi Kleen
2015-09-16 2:50 ` Andrew Morton
2015-09-16 2:55 ` Andi Kleen
2015-09-18 19:19 ` Andrew Morton
2015-09-19 20:16 ` Andi Kleen [this message]
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