On 6/14/26 08:13, Michael S. Tsirkin wrote:
Yes, I think it does work because we use -fno-strict-aliasing.
For bigger sizes we'll need packed because the addresses
could be unaligned.
...
For most host/guest pairs things simply work even for unaligned.
And yes, guest drivers do do this.
On classical pci, there are no transactions as such and
an unaligned access will be split anyway.
I'm saying, if you're talking about pass-through to real devices, that won't work. For
instance, AArch64 will trap unaligned accesses to Device memory.
You need to actually handle unaligned. Perhaps something like
/* Find unit to fit size and alignment of dst */
uintptr_t test = (uintptr_t)dst | size;
uintptr_t lsb = test & -test;
switch (lsb) {
case 1: // loop over uint8_t
case 2: // loop over uint16_t
case 4: // loop over uint32_t
default: // loop over uint64_t
}
with the expectation that normally we'll have aligned addresses and size such that the
loop will iterate once.
r~
