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

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] ?