Re: [Qemu-devel] RFC: fix run of 32 bits Linux executables on 64 bits targets

[Blue Swirl]

On 10/11/07, Thiemo Seufer <address@hidden> wrote:
> Fabrice Bellard wrote:
> > Thiemo Seufer wrote:
> >> Fabrice Bellard wrote:
> >>> J. Mayer wrote:
> >>>> Following the patches done for elfload32, it appeared to me that there
> >>>> were still problems that would prevent 32 bits executables to run on 64
> >>>> bits target in linux user mode emulation.
> >>>> [...]
> >>> Are you sure it is a good idea to try to add 32 bit executable support to
> >>> a 64 bit target ? In the end you will need to write a 64 bit to 32 bit
> >>> linux syscall converter which would mean duplicating all the linux-user
> >>> code of the corresponding 32 bit target (think of ioctls with strutures,
> >>> signals frames, etc...).
> >> I would think this feature will be limited to platforms which can handle
> >> 32bit and 64bit binaries with a single personality.
> >
> > I am not sure it is a common case !
> >
> > However, I suggest to emulate a 32 bit user linux system with a 64 bit
> > guest CPU running in 32 bit compatibily mode. It would be useful to test 64
> > bit CPUs in 32 bit compatibility mode. The only required modification in
> > linux user is to rename target_ulong so that it can have a different size
> > of the CPU word default size.
>
> Doesn't work for MIPS64, since it doesn't quite have a compatibility mode
> in the traditional sense. It needs to retain 64bit register width when
> running N32 ABI binaries. (Thus the somewhat odd overrides I added for
> the preliminary N32 support.)

CPU registers (and storage for full width registers) would still be 64
bits. The ABI uses of target_ulong need to be changed to, for example
abi_ulong so that the size can be changed.

Sparc64 does not have a compatibility mode either (except for address
masking), it can run Sparc32 binaries because of the cleverly designed
instruction set. Ops use full 64 bits of a register, but there are two
sets of CPU flags, 32 and 64 bits.