Re: [PATCH v6 8/8] linux-user: Load pie executables at upper memory

[Akihiko Odaki]

On 2023/08/02 18:34, Helge Deller wrote:
> On 8/2/23 10:44, Akihiko Odaki wrote:
> > On 2023/08/02 17:42, Helge Deller wrote:
> > > On 8/2/23 09:49, Akihiko Odaki wrote:
> > > > On 2023/08/02 8:27, Helge Deller wrote:
> > > > > Fix the elf loader to calculate a valid TASK_UNMAPPED_BASE address 
> > > > > for all
> > > > > 32-bit architectures, based on the GUEST_ADDR_MAX constant.
> > > > >
> > > > > Additionally modify the elf loader to load dynamic pie executables at
> > > > > around:
> > > > > ~ 0x5500000000  for 64-bit guest binaries on 64-bit host,
> > > > > - 0x00300000    for 32-bit guest binaries on 64-bit host, and
> > > > > - 0x00000000    for 32-bit guest binaries on 32-bit host.
> > > >
> > > > Why do you change guest addresses depending on the host?
> > >
> > > The addresses are guest-addresses.
> > > A 32-bit guest PIE can't be loaded at e.g. 0x5500000000,
> > > while a 64-bit guest PIE needs to be loaded at 0x5500000000.
> >
> > I mean, why do you use address 0x00000000 for 32-bit guest binaries on 
> > 32-bit host while you use address 0x00300000 on 64-bit host?
>
> To keep the memory pressure for the 32-bit qemu binary minimal.
> On 64-bit host we have the full 32-bit address space for the guest.
>
> Helge

That makes sense. I'm worried that using 0x00000000 may break NULL 
checks on the guest though.

Regards,
Akihiko Odaki