From: Arnd Bergmann > Sent: 04 March 2024 13:40 ... > > If not, then the test has to be fixed to only use word-aligned IPv6 > > addresses. > > Because of the gcc issue I mentioned, net/ipv6/ip6_checksum.c > and anything else that accesses misaligned ipv6 headers may need > to be changed as well. Marking in6_addr as '__packed __aligned(2)' > should be sufficient for that. This will prevent gcc from issuing > ldm or ldrd on ARMv6+ as well as making optimization based on > the two lower bits of the address being zero on x86 and others. Eh? x86 pretty much doesn't care unless you are using AVX. > The downside is that it forces 16-bit loads and stores to be > used on architectures that don't have efficient unaligned > access (armv5, alpha, mips, sparc and xtensa among others) > even when the IP headers are fully aligned. Aren't the later accesses to the header also going to fault? IIRC there is an skb_pull() call to ensure all the IP header is in the linear skb fragment? Perhaps there should be an skb_pull_aligned() that will ensure the data is 32bit aligned on systems where the misaligned accesses fault? There might still need to be something to stop gcc generating ldm/ldrd which can fault on systems where a normal register read wouldn't. Do any recent arm cpu have the strongarm 'feature' than ldm always took 16 clocks? David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
