Re: [PATCH v4 2/5] docs/about/deprecated: Deprecate the qemu-system-i386 binary

[Daniel P. Berrangé <berrange@xxxxxxxxxx>]

On Mon, Mar 06, 2023 at 02:25:46PM +0000, Daniel P. Berrangé wrote:
> On Mon, Mar 06, 2023 at 03:18:23PM +0100, Thomas Huth wrote:
> > On 06/03/2023 15.06, Daniel P. Berrangé wrote:
> > > On Mon, Mar 06, 2023 at 02:48:16PM +0100, Thomas Huth wrote:
> > > > On 06/03/2023 10.27, Daniel P. Berrangé wrote:
> > > > > On Mon, Mar 06, 2023 at 09:46:55AM +0100, Thomas Huth wrote:
> > > > > > [...] If a 32-bit CPU guest
> > > > > > +environment should be enforced, you can switch off the "long mode" 
> > > > > > CPU
> > > > > > +flag, e.g. with ``-cpu max,lm=off``.
> > > > > 
> > > > > I had the idea to check this today and this is not quite sufficient,
> > > > [...]
> > > > > A further difference is that qemy-system-i686 does not appear to 
> > > > > enable
> > > > > the 'syscall' flag, but I've not figured out where that difference is
> > > > > coming from in the code.
> > > > 
> > > > I think I just spotted this by accident in target/i386/cpu.c
> > > > around line 637:
> > > > 
> > > > #ifdef TARGET_X86_64
> > > > #define TCG_EXT2_X86_64_FEATURES (CPUID_EXT2_SYSCALL | CPUID_EXT2_LM)
> > > > #else
> > > > #define TCG_EXT2_X86_64_FEATURES 0
> > > > #endif
> > > 
> > > Hmm, so right now the difference between qemu-system-i386 and
> > > qemu-system-x86_64 is based on compile time conditionals. So we
> > > have the burden of building everything twice and also a burden
> > > of testing everything twice.
> > > 
> > > If we eliminate qemu-system-i386 we get rid of our own burden,
> > > but users/mgmt apps need to adapt to force qemu-system-x86_64
> > > to present a 32-bit system.
> > > 
> > > What about if we had qemu-system-i386 be a hardlink to
> > > qemu-system-x86_64, and then changed behaviour based off the
> > > executed binary name ?
> > 
> > We could also simply provide a shell script that runs:
> > 
> >  qemu-system-x86_64 -cpu qemu32 $*
> > 
> > ... that'd sounds like the simplest solution to me.
> 
> That woudn't do the right thing if the user ran 'qemu-system-i386 -cpu max'
> because their '-cpu max' would override the -cpu arg in the shell script
> that forced 32-bit mode.

It would also fail to work with SELinux, because policy restrictions
doesn't allow for an intermediate wrapper script to exec binaries.

With regards,
Daniel
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