On 8/13/19 9:12 AM, Bart Van Assche wrote: > On 8/12/19 7:53 PM, Jens Axboe wrote: >> On 8/12/19 8:01 PM, Bart Van Assche wrote: >>> Instead of declaring the whole structure packed, only declare non-aligned >>> members packed. This patch is an alternative way to fix the following gcc 9 >>> compiler warnings: >>> >>> eta.c: In function 'calc_thread_status': >>> eta.c:510:7: error: taking address of packed member of 'struct jobs_eta' may result in an unaligned pointer value [-Werror=address-of-packed-member] >>> 510 | je->rate); >>> | ~~^~~~~~ >>> eta.c:522:66: error: taking address of packed member of 'struct jobs_eta' may result in an unaligned pointer value [-Werror=address-of-packed-member] >>> 522 | calc_rate(unified_rw_rep, disp_time, io_bytes, disp_io_bytes, je->rate); >>> | ~~^~~~~~ >>> eta.c:523:64: error: taking address of packed member of 'struct jobs_eta' may result in an unaligned pointer value [-Werror=address-of-packed-member] >>> 523 | calc_iops(unified_rw_rep, disp_time, io_iops, disp_io_iops, je->iops); >>> | >> >> This seems fragile. Not that we change the struct all the time, or even often, >> but it'd be easy to add members and end up with different layout on 32-bit >> vs 64-bit. >> >> How do we improve on that? > > Hi Jens, > > Do you agree that the "BUILD_BUG_ON(sizeof(struct jobs_eta) != 160)" > statement added by the previous patch should catch such differences? 160 > bytes namely is the size of an entirely packed jobs_eta structure. I guess that's good enough, though it'd be nice to check for holes explicitly. I wonder if there's an easy way to do that, though... -- Jens Axboe
