[Qemu-devel] Re: linux-user issues

[Paul Brook <paul@codesourcery.com>]

> On Sat, 13 Mar 2010, Paul Brook wrote:
> > > a) elfload.c:859
> > >
> > >    #define TARGET_ELF_PAGESTART(_v) ((_v) & ~(unsigned
> > >  long)(TARGET_ELF_EXEC_PAGESIZE-1))
> > >
> > >    This means that for 64bit guest on a 32bit host the _v's value is
> > >    silently reduced to 32bit, the cast should be abi_ulong.
> > >
> > > b) mmap.c:428
> > >
> > >    real_start = start & qemu_host_page_mask;
> > >
> > >    Same thing basically qemu_host_page_mask is unsigned long and so
> > >    the upper bits are sliently cleared. Again qemu_host_page_mask
> > >    should probably be abi_ulong.
> > >
> > > The above two make elf binary with one of the segments above 4G load
> > > and run on 32bit guest only to fail well into execution and without
> > > any indication that it shouldn't have been allowed to run in the first
> > > place.
> >
> > I'd be amazed if these are the only two issues, and expect 64-bit guests
> > on 32-bit hosts to be generally unsafe.
> 
> These are the two issues i've been bitten by while trying to solve
> x86_64's far jumps, if you are okay with code silently misbehaving
> fine by me.

I never said this was ok behavior. Only that you've probably only discovered 
the tip of the iceberg.

Paul