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

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D5F4E3E8D@AcuExch.aculab.com>
Date:	Fri, 24 Jun 2016 09:17:07 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Phil Sutter' <phil@....cc>,
	Stephen Hemminger <shemming@...cade.com>
CC:	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

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.

	David