| Message ID | 20220520055940.2309280-1-kuba@kernel.org (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net-next] eth: mtk_eth_soc: silence the GCC 12 array-bounds warning | expand |
On Thu, May 19, 2022 at 10:59:40PM -0700, Jakub Kicinski wrote: > GCC 12 gets upset because in mtk_foe_entry_commit_subflow() > this driver allocates a partial structure. The writes are > within bounds. I'm wondering if the partial structure is worth it: struct mtk_flow_entry { union { struct hlist_node list; struct { struct rhash_head l2_node; struct hlist_head l2_flows; }; }; u8 type; s8 wed_index; u16 hash; union { struct mtk_foe_entry data; struct { struct mtk_flow_entry *base_flow; struct hlist_node list; struct {} end; } l2_data; }; struct rhash_head node; unsigned long cookie; }; It allocates upto l2_data.end struct rhash contains a single pointer So this is saving 8 or 16 bytes depending on architecture. I estimate the structure as a whole is at least 100 bytes on 32bit systems. I suppose it might make sense if this makes the allocation go from 129 bytes to <= 128, and the allocater is rounding up to the nearest power of 2? Andrew
On Fri, 20 May 2022 15:06:52 +0200 Andrew Lunn wrote: > On Thu, May 19, 2022 at 10:59:40PM -0700, Jakub Kicinski wrote: > > GCC 12 gets upset because in mtk_foe_entry_commit_subflow() > > this driver allocates a partial structure. The writes are > > within bounds. > > I'm wondering if the partial structure is worth it: > > struct mtk_flow_entry { > union { > struct hlist_node list; > struct { > struct rhash_head l2_node; > struct hlist_head l2_flows; > }; > }; > u8 type; > s8 wed_index; > u16 hash; > union { > struct mtk_foe_entry data; > struct { > struct mtk_flow_entry *base_flow; > struct hlist_node list; > struct {} end; > } l2_data; > }; > struct rhash_head node; > unsigned long cookie; > }; > > > It allocates upto l2_data.end > > struct rhash contains a single pointer > > So this is saving 8 or 16 bytes depending on architecture. > > I estimate the structure as a whole is at least 100 bytes on 32bit > systems. > > I suppose it might make sense if this makes the allocation go from 129 > bytes to <= 128, and the allocater is rounding up to the nearest power > of 2? Good point, I'm not sure what Felix prefers. I think isolating the necessary fields into a different structure and encapsulating that into something with the extra two members (or maybe the GROUP_MEMBER macro thing?) would be another way forward. I'd still like explicit feedback on the Makefile hack. Is it too ugly? We could wait for GCC 12 to get its act together was well, but I'm guessing Dave and I are not the only people who will upgrade to Fedora 36 and enter a world of pain...
diff --git a/drivers/net/ethernet/mediatek/Makefile b/drivers/net/ethernet/mediatek/Makefile index 45ba0970504a..611f7b4d4eb8 100644 --- a/drivers/net/ethernet/mediatek/Makefile +++ b/drivers/net/ethernet/mediatek/Makefile @@ -11,3 +11,8 @@ mtk_eth-$(CONFIG_NET_MEDIATEK_SOC_WED) += mtk_wed_debugfs.o endif obj-$(CONFIG_NET_MEDIATEK_SOC_WED) += mtk_wed_ops.o obj-$(CONFIG_NET_MEDIATEK_STAR_EMAC) += mtk_star_emac.o + +# FIXME: temporarily silence -Warray-bounds on non W=1 builds +ifndef KBUILD_EXTRA_WARN +CFLAGS_mtk_ppe.o += $(call cc-disable-warning, array-bounds) +endif
GCC 12 gets upset because in mtk_foe_entry_commit_subflow() this driver allocates a partial structure. The writes are within bounds. Silence these warnings for now, our build bot runs GCC 12 so we won't allow any new instances. Signed-off-by: Jakub Kicinski <kuba@kernel.org> --- CC: nbd@nbd.name CC: john@phrozen.org CC: sean.wang@mediatek.com CC: Mark-MC.Lee@mediatek.com CC: matthias.bgg@gmail.com --- drivers/net/ethernet/mediatek/Makefile | 5 +++++ 1 file changed, 5 insertions(+)