On 9/17/19 2:32 AM, Nathan Chancellor wrote: > Hi all, > > Clang recently added a new diagnostic in r371605, -Wsizeof-array-div, > that tries to warn when sizeof(X) / sizeof(Y) does not compute the > number of elements in an array X (i.e., sizeof(Y) is wrong). See that > commit for more details: > > https://github.com/llvm/llvm-project/commit/3240ad4ced0d3223149b72a4fc2a4d9b67589427 > > Some ethernet drivers have an instance of this warning due to receive > side scaling support: > > > ../drivers/net/ethernet/amd/xgbe/xgbe-dev.c:361:49: warning: expression > does not compute the number of elements in this array; element type is > 'u8' (aka 'unsigned char'), not 'u32' (aka 'unsigned int') > [-Wsizeof-array-div] > unsigned int key_regs = sizeof(pdata->rss_key) / sizeof(u32); > ~~~~~~~~~~~~~~ ^ > ../drivers/net/ethernet/amd/xgbe/xgbe-dev.c:361:49: note: place > parentheses around the 'sizeof(u32)' expression to silence this warning > > > ../drivers/net/ethernet/stmicro/stmmac/dwxgmac2_core.c:537:36: warning: > expression does not compute the number of elements in this array; > element type is 'u8' (aka 'unsigned char'), not 'u32' (aka 'unsigned > int') [-Wsizeof-array-div] > for (i = 0; i < (sizeof(cfg->key) / sizeof(u32)); i++) { > ~~~~~~~~ ^ > ../drivers/net/ethernet/stmicro/stmmac/dwxgmac2_core.c:537:36: note: > place parentheses around the 'sizeof(u32)' expression to silence this > warning > > > ../drivers/net/ethernet/synopsys/dwc-xlgmac-hw.c:2329:49: warning: > expression does not compute the number of elements in this array; > element type is 'u8' (aka 'unsigned char'), not 'u32' (aka 'unsigned > int') [-Wsizeof-array-div] > unsigned int key_regs = sizeof(pdata->rss_key) / sizeof(u32); > ~~~~~~~~~~~~~~ ^ > ../drivers/net/ethernet/synopsys/dwc-xlgmac-hw.c:2329:49: note: place > parentheses around the 'sizeof(u32)' expression to silence this warning > > > What is the reasoning behind having the key being an array of u8s but > seemlingly converting it into an array of u32s? It's not immediately
Probably because the ethtool functions that get and set the RSS key passes the key buffer in as a u8 pointer. Having said that, there's no reason that any casting can't be done in the ethtool callback functions, if needed (which I don't think it is, since the key buffer is used in memcpy() calls), instead. Thanks, Tom > apparent from reading over the code but I am not familiar with it so I > might be making a mistake. I assume this is intentional? If so, the > warning can be silenced and we'll send patches to do so but we want to > make sure we aren't actually papering over a mistake.> > Cheers! > Nathan >
