| Message ID | 20230214132025.1532147-1-arnd@kernel.org (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | Johannes Berg |
| Headers | show |
| Series | wifi: mac80211: avoid u32_encode_bits() warning | expand |
From: Arnd Bergmann <arnd@kernel.org> Date: Tue, 14 Feb 2023 14:20:21 +0100 > From: Arnd Bergmann <arnd@arndb.de> > > gcc-9 triggers a false-postive warning in ieee80211_mlo_multicast_tx() > for u32_encode_bits(ffs(links) - 1, ...), since ffs() can return zero > on an empty bitmask, and the negative argument to u32_encode_bits() > is then out of range: > > In file included from include/linux/ieee80211.h:21, > from include/net/cfg80211.h:23, > from net/mac80211/tx.c:23: > In function 'u32_encode_bits', > inlined from 'ieee80211_mlo_multicast_tx' at net/mac80211/tx.c:4437:17, > inlined from 'ieee80211_subif_start_xmit' at net/mac80211/tx.c:4485:3: > include/linux/bitfield.h:177:3: error: call to '__field_overflow' declared with attribute error: value doesn't fit into mask > 177 | __field_overflow(); \ > | ^~~~~~~~~~~~~~~~~~ > include/linux/bitfield.h:197:2: note: in expansion of macro '____MAKE_OP' > 197 | ____MAKE_OP(u##size,u##size,,) > | ^~~~~~~~~~~ > include/linux/bitfield.h:200:1: note: in expansion of macro '__MAKE_OP' > 200 | __MAKE_OP(32) > | ^~~~~~~~~ > > Newer compiler versions do not cause problems with the zero argument > because they do not consider this a __builtin_constant_p(). > It's also harmless since the hweight16() check already guarantees > that this cannot be 0. > > Replace the ffs() with an equivalent find_first_bit() check that > matches the later for_each_set_bit() style and avoids the warning. > > Fixes: 963d0e8d08d9 ("wifi: mac80211: optionally implement MLO multicast TX") > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > --- > net/mac80211/tx.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c > index defe97a31724..118648af979c 100644 > --- a/net/mac80211/tx.c > +++ b/net/mac80211/tx.c > @@ -4434,7 +4434,7 @@ static void ieee80211_mlo_multicast_tx(struct net_device *dev, > u32 ctrl_flags = IEEE80211_TX_CTRL_MCAST_MLO_FIRST_TX; > > if (hweight16(links) == 1) { > - ctrl_flags |= u32_encode_bits(ffs(links) - 1, > + ctrl_flags |= u32_encode_bits(find_first_bit(&links, 16) - 1, Uff, IIRC find_first_bit() matches __ffs() calling convention, not ffs() one. They're off-by-one from each other, which means you need to drop this `- 1`. As this branch happens only when hweight is 1 => @links has a bit set, it's safe to just use __ffs() here directly, but up to you. find_first_bit() is fine, too, since it will be optimized out to __ffs() at the end in this case. > IEEE80211_TX_CTRL_MLO_LINK); > > __ieee80211_subif_start_xmit(skb, sdata->dev, 0, ctrl_flags, Thanks, Olek
diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c index defe97a31724..118648af979c 100644 --- a/net/mac80211/tx.c +++ b/net/mac80211/tx.c @@ -4434,7 +4434,7 @@ static void ieee80211_mlo_multicast_tx(struct net_device *dev, u32 ctrl_flags = IEEE80211_TX_CTRL_MCAST_MLO_FIRST_TX; if (hweight16(links) == 1) { - ctrl_flags |= u32_encode_bits(ffs(links) - 1, + ctrl_flags |= u32_encode_bits(find_first_bit(&links, 16) - 1, IEEE80211_TX_CTRL_MLO_LINK); __ieee80211_subif_start_xmit(skb, sdata->dev, 0, ctrl_flags,