On Tue, Sep 17, 2019 at 6:27 AM Jose Abreu <jose.ab...@synopsys.com> wrote: > > From: David Laight <david.lai...@aculab.com> > Date: Sep/17/2019, 11:36:21 (UTC+00:00) > > > From: Jose Abreu > > > Sent: 17 September 2019 08:59 > > > From: Nathan Chancellor <natechancel...@gmail.com> > > > Date: Sep/17/2019, 08:32:32 (UTC+00:00) > > > > > > > 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: > > ... > > > > ../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); > > > > ~~~~~~~~~~~~~~ ^ > > ... > > > > 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 > > > > 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. > > > > > > This is because we write 32 bits at a time to the reg but internally the > > > driver uses 8 bits to store the array. If you look at > > > dwxgmac2_rss_configure() you'll see that cfg->key is casted to u32 which > > > is the value we use in HW writes. Then the for loop just does the math > > > to check how many u32's has to write. > > > > That stinks of a possible misaligned data access..... > > It's possible to happen only if structure field is not aligned. I guess > I can either change all to u32 or just __align the field of the struct
Would __aligning the struct still produce the warning? It's good to know that this case is intentional, but I would like to consider other instances of it before we seriously consider turning it off. If the driver can be rewritten to just make use of u32, I would find that preferrable. -- Thanks, ~Nick Desaulniers
