On 8 June 2016 at 10:29, Laurent Vivier <laur...@vivier.eu> wrote: > > > Le 07/06/2016 à 23:08, Peter Maydell a écrit : >> On 7 June 2016 at 20:36, Laurent Vivier <laur...@vivier.eu> wrote: >>> >>> >>> Le 27/05/2016 à 16:52, Peter Maydell a écrit : >>>> host_to_target_siginfo() is implemented by a combination of >>>> host_to_target_siginfo_noswap() followed by tswap_siginfo(). >>>> The first of these two functions assumes that the target_siginfo_t >>>> it is writing to is correctly aligned, but the pointer passed >>>> into host_to_target_siginfo() is directly from the guest and >>>> might be misaligned. Use a local variable to avoid this problem. >>>> (tswap_siginfo() does now correctly handle a misaligned destination.) >>> >>> You mean the pointer from the guest can not be correctly aligned for the >>> guest? >> >> Might not be correctly aligned for the host (for that matter >> it might not be correctly aligned for the guest, >> if the guest is being malicious or buggy, but it's the >> host alignment we care about.) > > Because of the "abi_ulong _addr", I think this structure is always > aligned for the guest.
No, because the address of the structure in guest memory comes from a pointer passed to us by the guest. The guest could pass any value at all that it likes for that pointer including one that is arbitrarily misaligned. I think it's pretty much always a bug to do a direct access to a structure field that's in guest memory, though we do it a fair bit and get away with it because x86-64 doesn't have alignment restrictions. thanks -- PMM
