linux-kernel - Re: [PATCH v2] Fix initializing a static union variable

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Date: Sat, 22 Jun 2024 08:35:46 +1000
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Yabin Cui <yabinc@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Steffen Klassert <steffen.klassert@...unet.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH v2] Fix initializing a static union variable

On Fri, Jun 21, 2024 at 02:18:19PM -0700, Yabin Cui wrote:
> saddr_wildcard is a static union variable initialized with {}.
> 
> Empty brace initialization of union types is unspecified prior to C23,
> and even in C23, it doesn't guarantee zero initialization of all fields
> (see sections 4.5 and 6.2 in
> https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2900.htm).

What about all the other places in the kernel that use the same
idiom? A grep shows that there are more than a hundred spots in
the kernel where {} is used to initialise a union.

$ git grep '=[[:blank:]]*{}' | grep union | wc -l
123
$

Also what if the union is embedded into a struct.  Does it get
initialised fully or not? If not then you've got over 5000 {}
initialisations to work through.

$ git grep '=[[:blank:]]*{}' | wc -l
5102
$

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt