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[PATCH 6/6] kconfig option for TRIM_UNUSED_EXPSYMS

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  [PATCH 6/6] kconfig option for TRIM_UNUSED_EXPSYMS Nicolas Pitre <nicolas.pitre@linaro.org> - 2016-02-08 21:50 +0100
    Re: [PATCH 6/6] kconfig option for TRIM_UNUSED_EXPSYMS Rusty Russell <rusty@rustcorp.com.au> - 2016-02-09 05:00 +0100
      Re: [PATCH 6/6] kconfig option for TRIM_UNUSED_EXPSYMS Nicolas Pitre <nicolas.pitre@linaro.org> - 2016-02-09 05:40 +0100
      Re: [PATCH 6/6] kconfig option for TRIM_UNUSED_EXPSYMS Sam Ravnborg <sam@ravnborg.org> - 2016-02-09 12:50 +0100
    Re: [PATCH 6/6] kconfig option for TRIM_UNUSED_EXPSYMS Christoph Hellwig <hch@infradead.org> - 2016-02-09 14:30 +0100
      Re: [PATCH 6/6] kconfig option for TRIM_UNUSED_EXPSYMS "Austin S. Hemmelgarn" <ahferroin7@gmail.com> - 2016-02-09 14:40 +0100
      Re: [PATCH 6/6] kconfig option for TRIM_UNUSED_EXPSYMS Nicolas Pitre <nicolas.pitre@linaro.org> - 2016-02-09 18:10 +0100
        Re: [PATCH 6/6] kconfig option for TRIM_UNUSED_EXPSYMS Rusty Russell <rusty@rustcorp.com.au> - 2016-02-10 00:40 +0100

#1329551 — [PATCH 6/6] kconfig option for TRIM_UNUSED_EXPSYMS

The config option to enable it all.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
---
 init/Kconfig | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/init/Kconfig b/init/Kconfig
index 22320804fb..893c4979a9 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1990,6 +1990,22 @@ config MODULE_COMPRESS_XZ
 
 endchoice
 
+config TRIM_UNUSED_EXPSYMS
+	bool "Trim unused exported symbols"
+	depends on MODULES && !UNUSED_SYMBOLS
+	help
+	  The kernel and some modules make many symbols available for
+	  other modules to use via EXPORT_SYMBOL() and variants. Depending
+	  on the set of modules being selected in your kernel configuration,
+	  many of those exported symbols might never be used.
+
+	  This option allows for unused exported symbols to be dropped from
+	  the build. In turn, this provides the compiler more opportunities
+	  (especially when using LTO) for optimizing the code and reducing
+	  binary size.  This might have some security advantages as well.
+
+	  If unsure say N.
+
 endif # MODULES
 
 config MODULES_TREE_LOOKUP
-- 
2.5.0

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#1329887

Nicolas Pitre <nicolas.pitre@linaro.org> writes:
> The config option to enable it all.
>
> Signed-off-by: Nicolas Pitre <nico@linaro.org>

Nice series!  In case you need it, here's my Ack.  Despite the overlap
with modules, it's all build trickery, so best via Sam's tree.

Acked-by: Rusty Russell <rusty@rustcorp.com.au>

Thanks,
Rusty.

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#1329900

On Tue, 9 Feb 2016, Rusty Russell wrote:

> Nicolas Pitre <nicolas.pitre@linaro.org> writes:
> > The config option to enable it all.
> >
> > Signed-off-by: Nicolas Pitre <nico@linaro.org>
> 
> Nice series!  In case you need it, here's my Ack.  Despite the overlap
> with modules, it's all build trickery, so best via Sam's tree.
> 
> Acked-by: Rusty Russell <rusty@rustcorp.com.au>

Thanks


Nicolas

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#1330127

> 
> so best via Sam's tree.
That was some years ago ;-)

	Sam

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#1330231

On Mon, Feb 08, 2016 at 03:28:35PM -0500, Nicolas Pitre wrote:
> The config option to enable it all.

Just enable it by default..

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#1330233

On 2016-02-09 08:28, Christoph Hellwig wrote:
> On Mon, Feb 08, 2016 at 03:28:35PM -0500, Nicolas Pitre wrote:
>> The config option to enable it all.
>
> Just enable it by default..
>
I doubt we care too much about third party modules, but enabling this by 
default will likely cause at least some of them to stop working.  At the 
very least, we need the config option, even if it's enabled by default.

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#1330491

On Tue, 9 Feb 2016, Christoph Hellwig wrote:

> On Mon, Feb 08, 2016 at 03:28:35PM -0500, Nicolas Pitre wrote:
> > The config option to enable it all.
> 
> Just enable it by default..

:-)

Viro took the opposite view with this patch:

http://lkml.org/lkml/2016/2/3/1068

where he's ensuring that no exports are dropped, even if obviously 
they're not used (otherwise some complaints would have come about).  So 
I'm not sure if having this turned on by default is a good thing.

But I don't mind being convinced otherwise.


Nicolas

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#1330774

Nicolas Pitre <nicolas.pitre@linaro.org> writes:
> On Tue, 9 Feb 2016, Christoph Hellwig wrote:
>
>> On Mon, Feb 08, 2016 at 03:28:35PM -0500, Nicolas Pitre wrote:
>> > The config option to enable it all.
>> 
>> Just enable it by default..
>
> :-)
>
> Viro took the opposite view with this patch:
>
> http://lkml.org/lkml/2016/2/3/1068
>
> where he's ensuring that no exports are dropped, even if obviously 
> they're not used (otherwise some complaints would have come about).  So 
> I'm not sure if having this turned on by default is a good thing.
>
> But I don't mind being convinced otherwise.

People do build out-of-tree modules.  Dropping support for that would
simplify our lives, but seems fairly controversial :)

Cheers,
Rusty.

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