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

[Blue Swirl]

On 10/12/07, J. Mayer <address@hidden> wrote:
> On Thu, 2007-10-11 at 22:26 +0300, Blue Swirl wrote:
> > On 10/10/07, Fabrice Bellard <address@hidden> 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.
> >
> > I made a patch to rename target_ulong/long to abi_ulong/long and also
> > add a new emulator target that uses the 32 bit ABI with 64 bit CPU.
> >
> > Some Sparc32 binaries run, others don't, possibly indicating bugs in
> > the Sparc64 emulation!
> >
> > The patch is quite large because of the renaming, but this shouldn't
> > have effect to any other target. Any comments?
>
> Great !
> The patch seems safe, at first look, then I noticed a few things that
> are not correct or may be improved:
> * In linux-user/main.c: PowerPC DCR access should keep using
> target_ulong. This is a hardware bus, not an ABI dependent stuff. If a
> 32 bits cast is needed, it would be done in the micro-ops that handle
> the DCR bus accesses.
> * in linux-user/qemu.h: why is there still a OVERRIDE_ELF_CLASS
> variable, when checking TARGET_ABI32 should be sufficient ? It seems to
> me that having 2 defines which are, in fact, synonymous may be a source
> of confusion.
> * in configure: you also added a sparc64-softmmu target, which seems not
> related with this particular patch.
> * in configure: why add a specific TARGET_ABI32_DIR variable for that
> case ? It seems to me that a TARGET_ABI_DIR variable could be useful for
> all targets. Let me give an example: I want to add a ppcemb-linux-user
> target, emulating a PowerPC 32 with 64 bits registers and SIMD
> extensions but I don't want to duplicate the linux-user/ppc
> subdirectory. Having a TARGET_ABI_DIR available for all targets would
> solve my problem. In fact, even ppc and ppc64 could be merged... As you
> need this feature in your case, I think it would be a good idea to add
> it for all targets. And then, the kludge in Makefile.target could be
> replaced by:
> -CPPFLAGS+=-I$(SRC_PATH)/linux-user -I
> $(SRC_PATH)/linux-user/$(TARGET_ARCH)
> +CPPFLAGS+=-I$(SRC_PATH)/linux-user -I
> $(SRC_PATH)/linux-user/$(TARGET_ABI_DIR)
> which is simpler and easier to understand, imho.

Thanks, I updated the patch to reflect your comments. Is the ppcemb
part correct or should just use existing values?

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