From: Marc Kleine-Budde > Sent: 08 February 2021 13:16 > > On 04.02.2021 17:26:13, Arnd Bergmann wrote: > > From: Arnd Bergmann <arnd@xxxxxxxx> > > > > struct ucan_message_in contains member with 4-byte alignment > > but is itself marked as unaligned, which triggers a warning: > > > > drivers/net/can/usb/ucan.c:249:1: warning: alignment 1 of 'struct ucan_message_in' is less than 4 [- > Wpacked-not-aligned] > > > > Mark the outer structure to have the same alignment as the inner > > one. > > > > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx> > > Applied to linux-can-next/testing. I've just had a look at that file. Are any of the __packed or __aligned actually required at all. AFAICT there is one structure that would have end-padding. But I didn't actually spot anything validating it's length. Which may well mean that it is possible to read off the end of the USB receive buffer - plausibly into unmapped addresses. I looked because all the patches to 'fix' the compiler warning are dubious. Once you've changed the outer alignment (eg of a union) then the compiler will assume that any pointer to that union is aligned. So any _packed() attributes that are required for mis-aligned accesses get ignored - because the compiler knows the pointer must be aligned. So while the changes remove the warning, they may be removing support for misaligned addresses. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
