On Tue, Mar 23, 2021 at 7:37 AM kernel test robot <lkp@xxxxxxxxx> wrote: > > tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master > head: 84196390620ac0e5070ae36af84c137c6216a7dc > commit: 97e4910232fa1f81e806aa60c25a0450276d99a2 linux/compiler-clang.h: define HAVE_BUILTIN_BSWAP* > date: 9 days ago > config: mips-randconfig-r023-20210322 (attached as .config) > compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 78a65cd945d006ff02f9d24d9cc20a302ed93b08) > reproduce (this is a W=1 build): > wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross > chmod +x ~/bin/make.cross > # install mips cross compiling tool for clang build > # apt-get install binutils-mips-linux-gnu > # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=97e4910232fa1f81e806aa60c25a0450276d99a2 > git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git > git fetch --no-tags linus master > git checkout 97e4910232fa1f81e806aa60c25a0450276d99a2 > # save the attached .config to linux build tree > COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=mips > > If you fix the issue, kindly add following tag as appropriate > Reported-by: kernel test robot <lkp@xxxxxxxxx> > > All warnings (new ones prefixed by >>): > > drivers/net/ethernet/chelsio/cxgb4/sge.c:814:28: warning: unused function 'calc_tx_descs' [-Wunused-function] > static inline unsigned int calc_tx_descs(const struct sk_buff *skb, > ^ > >> drivers/net/ethernet/chelsio/cxgb4/sge.c:2396:13: warning: stack frame size of 1168 bytes in function 'ethofld_xmit' [-Wframe-larger-than=] > static void ethofld_xmit(struct net_device *dev, struct sge_eosw_txq *eosw_txq) > ^ > 2 warnings generated. This looks related to a warning we saw on powerpc. I've tried digging into it a little bit more, but all I found is that the use of __builtin_bswap32() changes the inlining decisions but doesn't actively cause worse code. In fact, if I force the inlining like this: --- a/drivers/net/ethernet/chelsio/cxgb4/sge.c +++ b/drivers/net/ethernet/chelsio/cxgb4/sge.c @@ -2257,7 +2257,7 @@ static void *write_eo_wr(struct adapter *adap, struct sge_eosw_txq *eosw_txq, return cpl; } -static int ethofld_hard_xmit(struct net_device *dev, +static __attribute__((flatten)) __always_inline int ethofld_hard_xmit(struct net_device *dev, struct sge_eosw_txq *eosw_txq) { struct port_info *pi = netdev2pinfo(dev); @@ -2393,7 +2393,7 @@ static int ethofld_hard_xmit(struct net_device *dev, return ret; } -static void ethofld_xmit(struct net_device *dev, struct sge_eosw_txq *eosw_txq) +static noinline void ethofld_xmit(struct net_device *dev, struct sge_eosw_txq *eosw_txq) { struct sk_buff *skb; int pktcount, ret; I see a different effect: the function's frame grows to 2232 bytes with the open-coded bswap32 slightly less at 2200 bytes with the builtin bswap32, all because of too many variables getting spilled. On the other hand, marking ethofld_hard_xmit as flatten+noinline, I don't get these spills with either version of bswap32, and the stack usage of ethofld_hard_xmit()/ethofld_xmit() goes down to 472+112 bytes. If I remove -fsanitize=alignment, the total stack size for these functions is no more than 368 bytes regardless of the inlining or the bswap32() implementation. I would conclude that there is something wrong in clang that leads to badly optimized code in this file, but that my __builtin_bswap32() change is only what triggers the right conditions here, not the root cause. Arnd
