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

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 0

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.




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