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Re: kern/54486: athn driver panics on arm

The following reply was made to PR kern/54486; it has been noted by GNATS.

From: Andreas Gustafsson <>
Cc: (Andreas Gustafsson)
Subject: Re: kern/54486: athn driver panics on arm
Date: Fri, 23 Aug 2019 22:57:52 +0300

 Looks like gcc is optimizing the memcpy() call on line 2528 of
 src/sys/dev/usb/if_athn_usb.c into an unaligned 32-bit store:
                 txf = (struct ar_tx_frame *)&htc[1];
                 memset(txf, 0, sizeof(*txf));
                 txf->data_type = AR_HTC_NORMAL;
                 txf->node_idx = sta_index;
                 txf->vif_idx = 0;
                 txf->tid = tid;
 The fields at the beginning and end of *txf are being assigned to, so
 only the middle part really needs the memset()ting, and gcc apparently
 figures the way to do that is to store a 32-bit word of zeros there,
 at an unaligned address.
 I would not be surprised if this optimizaion is also breaking other
 parts of the arm kernel.  Does anyone know the right way to fix this?
 Andreas Gustafsson,

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