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

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.