netdev - Re: [iproute PATCH v3 0/6] Big C99 style initializer rework

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Message-ID: <20160624114753.GB28345@orbyte.nwl.cc>
Date:	Fri, 24 Jun 2016 13:47:53 +0200
From:	Phil Sutter <phil@....cc>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	Stephen Hemminger <shemming@...cade.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	David Ahern <dsa@...ulusnetworks.com>,
	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	Julien Floret <julien.floret@...nd.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [iproute PATCH v3 0/6] Big C99 style initializer rework

Hi,

On Fri, Jun 24, 2016 at 09:17:07AM +0000, David Laight wrote:
> From: Phil Sutter
> > Sent: 23 June 2016 18:34
> >
> > This is v3 of my C99-style initializer related patch series.
> ...
> 
> It would be interesting to know how this affect the kernel code size?
> 
> While gcc will generate a memset() call for 'struct foo = {0}' if you
> initialise some members it might generate explicit zeroing instructions
> for all the other words of the structure.
> 
> I've seen gcc use memset() to zero the end of a structure, it may use
> memset() for large gaps earlier in the structure.
> 
> But if you initialise a byte half way down you are very unlikely to
> get a single memset() and then a write to the single location.

I did a standard build ('make distclean; make') before and after this
commit in my tree. The 'ip' binary didn't change in size at all (quite
surprising), the 'tc' binary shrunk by 48 bytes.

Cheers, Phil