netdev - Re: [PATCH net-next v12 13/22] ovpn: implement peer lookup logic

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Message-ID: <Z08tV5vQe2S4iawi@hog>
Date: Tue, 3 Dec 2024 17:09:59 +0100
From: Sabrina Dubroca <sd@...asysnail.net>
To: Antonio Quartulli <antonio@...nvpn.net>
Cc: Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
	ryazanov.s.a@...il.com, Simon Horman <horms@...nel.org>,
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Donald Hunter <donald.hunter@...il.com>,
	Shuah Khan <shuah@...nel.org>, Andrew Lunn <andrew@...n.ch>
Subject: Re: [PATCH net-next v12 13/22] ovpn: implement peer lookup logic

2024-12-03, 15:58:17 +0100, Antonio Quartulli wrote:
> On 02/12/2024 16:07, Antonio Quartulli wrote:
> [...]
> > +#define ovpn_get_hash_slot(_key, _key_len, _tbl) ({	\
> > +	typeof(_tbl) *__tbl = &(_tbl);			\
> > +	jhash(_key, _key_len, 0) % HASH_SIZE(*__tbl);	\
> > +})
> > +
> > +#define ovpn_get_hash_head(_tbl, _key, _key_len) ({		\
> > +	typeof(_tbl) *__tbl = &(_tbl);				\
> > +	&(*__tbl)[ovpn_get_hash_slot(_key, _key_len, *__tbl)];	\
> > +})
> 
> clang a reporting various warnings like this:
> 
> ../drivers/net/ovpn/peer.c:406:9: warning: variable '__tbl' is uninitialized
> when used within its own initialization [-Wuninitialized]
>   406 |         head = ovpn_get_hash_head(ovpn->peers->by_id, &peer_id,
>       |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   407 |                                   sizeof(peer_id));
>       |                                   ~~~~~~~~~~~~~~~~
> ../drivers/net/ovpn/peer.c:179:48: note: expanded from macro
> 'ovpn_get_hash_head'
>   179 |         &(*__tbl)[ovpn_get_hash_slot(_key, _key_len, *__tbl)];  \
>       |                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~
> ../drivers/net/ovpn/peer.c:173:26: note: expanded from macro
> 'ovpn_get_hash_slot'
>   173 |         typeof(_tbl) *__tbl = &(_tbl);                  \
>       |                       ~~~~~     ^~~~
> 
> Anybody willing to help me understand this issue?
> 
> I have troubles figuring out how __tbl is being used uninitialized.
> I wonder if the parameters naming is fooling clang (or me) somehow.

Not really a solution to this specific issue, but do you actually need
ovpn_get_hash_slot as a separate macro? AFAICT all users could also be
converted to ovpn_get_hash_head, then you can merge ovpn_get_hash_slot
into ovpn_get_hash_head and maybe clang won't get confused?

No guarantee that this fixes anything (except saving one or two lines
in a few functions).

-- 
Sabrina