Re: [PATCH net-next 08/11] ath9k: work around false-positive gcc warning

Kalle Valo
2020-11-07T11:18:20Z

Johannes Berg <johannes@sipsolutions.net> writes:

> On Mon, 2020-11-02 at 18:26 +0200, Kalle Valo wrote:
>> Arnd Bergmann <arnd@kernel.org> writes:
>>
>> > From: Arnd Bergmann <arnd@arndb.de>
>> >
>> > gcc-10 shows a false-positive warning with CONFIG_KASAN:
>> >
>> > drivers/net/wireless/ath/ath9k/dynack.c: In function 'ath_dynack_sample_tx_ts':
>> > include/linux/etherdevice.h:290:14: warning: writing 4 bytes into a region of size 0 [-Wstringop-overflow=]
>> > 290 | *(u32 *)dst = *(const u32 *)src;
>> > | ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~
>> >
>> > Until gcc is fixed, work around this by using memcpy() in place
>> > of ether_addr_copy(). Hopefully gcc-11 will not have this problem.
>> >
>> > Link: https://godbolt.org/z/sab1MK
>> > Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97490
>> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>> > ---
>> > drivers/net/wireless/ath/ath9k/dynack.c | 6 ++++++
>> > 1 file changed, 6 insertions(+)
>> >
>> > diff --git a/drivers/net/wireless/ath/ath9k/dynack.c b/drivers/net/wireless/ath/ath9k/dynack.c
>> > index fbeb4a739d32..e4eb96b26ca4 100644
>> > --- a/drivers/net/wireless/ath/ath9k/dynack.c
>> > +++ b/drivers/net/wireless/ath/ath9k/dynack.c
>> > @@ -247,8 +247,14 @@ void ath_dynack_sample_tx_ts(struct ath_hw *ah, struct sk_buff *skb,
>> > ridx = ts->ts_rateindex;
>> >
>> > da->st_rbf.ts[da->st_rbf.t_rb].tstamp = ts->ts_tstamp;
>> > +#if defined(CONFIG_KASAN) && (CONFIG_GCC_VERSION >= 100000) && (CONFIG_GCC_VERSION < 110000)
>> > + /* https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97490 */
>> > + memcpy(da->st_rbf.addr[da->st_rbf.t_rb].h_dest, hdr->addr1, ETH_ALEN);
>> > + memcpy(da->st_rbf.addr[da->st_rbf.t_rb].h_src, hdr->addr2, ETH_ALEN);
>> > +#else
>> > ether_addr_copy(da->st_rbf.addr[da->st_rbf.t_rb].h_dest, hdr->addr1);
>> > ether_addr_copy(da->st_rbf.addr[da->st_rbf.t_rb].h_src, hdr->addr2);
>> > +#endif
>>
>> Isn't there a better way to handle this? I really would not want
>> checking for GCC versions become a common approach in drivers.
>>
>> I even think that using memcpy() always is better than the ugly ifdef.
>
> If you put memcpy() always somebody will surely go and clean it up to
> use ether_addr_copy() soon ...

I can always add a comment and hope that the cleanup people read
comments :) I did that now in the pending branch:

https://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git/commit/?h=pending&id=25cfc077bd7a798d1aa527ad2aa9932bb3284376

Does that look ok? I prefer that over the ifdef.

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