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Re: [PATCH v4 2/5] docs/about/deprecated: Deprecate the qemu-system-i386
From: |
Daniel P . Berrangé |
Subject: |
Re: [PATCH v4 2/5] docs/about/deprecated: Deprecate the qemu-system-i386 binary |
Date: |
Mon, 6 Mar 2023 14:06:08 +0000 |
User-agent: |
Mutt/2.2.9 (2022-11-12) |
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 ?
ie if running qemu-system-i386, we could present a 32-bit CPU by
default. We eliminate all of our double compilation burden still.
We still have extra testing burden, but it is in a fairly narrow
area, so does not imply x2 the testing burden just $small-percentage
extra testing ? That would means apps/users would not need to change
at all, but we still get most of the win we're after on the
QEMU side
Essentially #ifdef TARGET_X86_64 would be change 'if (is_64bit) {...}'
in a handful of places, with 'bool is_64bit' initialized in main() from
argv[0] ?
With regards,
Daniel
--
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- [PATCH v4 0/5] Deprecate system emulation support for 32-bit x86 and arm hosts, Thomas Huth, 2023/03/06
- [PATCH v4 2/5] docs/about/deprecated: Deprecate the qemu-system-i386 binary, Thomas Huth, 2023/03/06
- Re: [PATCH v4 2/5] docs/about/deprecated: Deprecate the qemu-system-i386 binary, Daniel P . Berrangé, 2023/03/06
- Re: [PATCH v4 2/5] docs/about/deprecated: Deprecate the qemu-system-i386 binary, Thomas Huth, 2023/03/06
- Re: [PATCH v4 2/5] docs/about/deprecated: Deprecate the qemu-system-i386 binary,
Daniel P . Berrangé <=
- Re: [PATCH v4 2/5] docs/about/deprecated: Deprecate the qemu-system-i386 binary, Thomas Huth, 2023/03/06
- Re: [PATCH v4 2/5] docs/about/deprecated: Deprecate the qemu-system-i386 binary, Daniel P . Berrangé, 2023/03/06
- Re: [PATCH v4 2/5] docs/about/deprecated: Deprecate the qemu-system-i386 binary, Daniel P . Berrangé, 2023/03/06
- Re: [PATCH v4 2/5] docs/about/deprecated: Deprecate the qemu-system-i386 binary, Philippe Mathieu-Daudé, 2023/03/06
[PATCH v4 1/5] docs/about/deprecated: Deprecate 32-bit x86 hosts for system emulation, Thomas Huth, 2023/03/06
[PATCH v4 5/5] gitlab-ci.d/crossbuilds: Drop the 32-bit arm system emulation jobs, Thomas Huth, 2023/03/06
[PATCH v4 3/5] gitlab-ci.d/crossbuilds: Drop the i386 system emulation job, Thomas Huth, 2023/03/06
[PATCH v4 4/5] docs/about/deprecated: Deprecate 32-bit arm hosts for system emulation, Thomas Huth, 2023/03/06