Re: [PATCH net-next 07/15] batman-adv: ensure u16 aligned mac address in structs

[Sven Eckelmann <sven@narfation.org>]

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https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260831135117.574836-1-sw%40simonwunderlich.de?part=7

> > An u8 array in structures have a natural alignment of only 1 byte. An
> > u8[ETH_ALEN] array must therefore be assumed to only be 1 byte aligned. But
> > many etherdevices.h functions are requiring a 2 byte (u16) alignment.
> >
> > All these addresses were either on the start of a struct or after a struct
> > member which required at least an alignment of 2 byte. Still, annote all
> > u8[ETH_ALEN] arrays on the stack as __aligned(2) to make sure that this
> > assumption isn't broken by other modifications inside the structs.
> 
> Discovered by: gpt-5-6-sol, opus-5 · Missed by: sashiko-gemini
> Should "arrays on the stack" read "arrays in structs" here?

Yes, copy+paste error. Minor for this PR

> > diff --git a/net/batman-adv/types.h b/net/batman-adv/types.h
> > index 99667f632d4d..c42a4aa8f41a 100644
> > --- a/net/batman-adv/types.h
> > +++ b/net/batman-adv/types.h
> 
> [ ... ]
> 
> > @@ -634,12 +634,12 @@ struct batadv_hardif_neigh_node {
> >  	struct hlist_node list;
> >  
> >  	/** @addr: the MAC address of the neighboring interface */
> > -	u8 addr[ETH_ALEN];
> > +	u8 addr[ETH_ALEN] __aligned(2);
> >  
> >  	/**
> >  	 * @orig: the address of the originator this neighbor node belongs to
> >  	 */
> > -	u8 orig[ETH_ALEN];
> > +	u8 orig[ETH_ALEN] __aligned(2);
> 
> Discovered by: gpt-5-6-sol, opus-5 · Missed by: sashiko-gemini
> Is the claim "All these addresses were either on the start of a struct or
> after a struct member which required at least an alignment of 2 byte"
> accurate for batadv_hardif_neigh_node.orig?
> 
> That member directly follows u8 addr[ETH_ALEN], which only requires 1 byte
> alignment; orig ends up on an even offset because ETH_ALEN happens to be
> even, not because the preceding member forces 2 byte alignment.  Would it
> be worth rewording that sentence?

But the struct member required indirectly an aligned of 2 bytes

Regards,
	Sven

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