Re: [Qemu-devel] [PATCH v2 06/10] elfload: only give abi_long/ulong the alignment specified by the target

[Paolo Bonzini <pbonzini@redhat.com>]

Il 04/04/2013 16:37, Peter Maydell ha scritto:
>> Regarding the others, none of them are in target-generic places, and
>> > none of them affect m68k (ARM only uses non-standard alignment for llong):
>> >
>> > - linux-user/mips64/syscall.h is correct with target_ulong, and in
>> > general MIPS is best left as it is (it often uses uint32_t/uint64_t or
>> > target_long/ulong explicitly so that n32 is handled correctly).
> Hmm, is this really right? target_ulong before this patch would
> have had an explicit alignment attribute, and it no longer does.
> So if you're running a mips64 guest on an m68k host then you'll
> now get structs with the natural m68k alignment rather than the
> desired mips64 alignment...

Note that target_ulong and abi_ulong would have different sizes.  Better
to get alignment wrong on m68k, than size wrong on all platforms. :)

Also I think this should not be a problem.  These structures have no
holes in them, the padding is always written down explicitly and they
are accessed (or should be) via copy_from/to_user.

> (I can entirely believe that we get this wrong in a lot of
> places, and that in theory just about anything in a target_
> struct needs an alignment specifier.)

Yes, or more simply just use abi_* types.  It doesn't help that
potential problems would only show up on m68k.

Paolo