linux, rvy: add default QEMU -cpu flags

[heshamelmatary]

Currently the launch target will add -cpu codasip-a730 only if --riscv-cheri-isa experimental_std093 is passed, and will discard -cpu if not. Discarding -cpu will result in a CHERI-enabled RVY QEMU, but with extended CHERI flags/features disabled such as cheri_pte, cheri_levels, etc, in the QEMU 7.1 branch.

This PR fixes this by:
1- Always pass -cpu rv64,cheri_pte,cheri_levels for CHERI-Linux by default, without having to check for the --riscv-cheri-isa flag.
2- Use a more generic -cpu rv64 and not codasip-a730.

[arichardson]

Can you do this globally instead of just for Linux?

[heshamelmatary]

Can you do this globally instead of just for Linux?

@arichardson I have now moved this to run_qemu's init. We can also probably remove this check in favour of the change in this PR

[paul-metzger]

Can you do this globally instead of just for Linux?

@arichardson I have now moved this to run_qemu's init. We can also probably remove this check in favour of the change in this PR

It looks like we can't remove the check and the corresponding if and else branches entirely because self._qemu_arch_suffix wouldn't be set. If we want to remove the code that sets -cpu and drop l730 support, then we could refactor the if branch to

if riscv_cheri_isa is RiscvCheriISA.EXPERIMENTAL_STD093:
                self._qemu_arch_suffix = f"riscv{xlen}cheristd"
else:
                self._qemu_arch_suffix = f"riscv{xlen}cheri"

so that _qemu_arch_suffix is still set.

[arichardson]

Can you place this in the qemu options init instead?

It just needs to be updated to use
xtarget.is_experimental_cheri093_std(self.config) instead of just checking the command line flag.

And yes we can use the generic CPU instead of a730

[arichardson]

Can you place this in the qemu options init instead?

It just needs to be updated to use xtarget.is_experimental_cheri093_std(self.config) instead of just checking the command line flag.

And yes we can use the generic CPU instead of a730

If the problem is that the config argument is not available there we could probably just add it.

[heshamelmatary]

this check

Can you do this globally instead of just for Linux?

@arichardson I have now moved this to run_qemu's init. We can also probably remove this check in favour of the change in this PR

It looks like we can't remove the check and the corresponding if and else branches entirely because self._qemu_arch_suffix wouldn't be set. If we want to remove the code that sets -cpu and drop l730 support, then we could refactor the if branch to

if riscv_cheri_isa is RiscvCheriISA.EXPERIMENTAL_STD093:
                self._qemu_arch_suffix = f"riscv{xlen}cheristd"
else:
                self._qemu_arch_suffix = f"riscv{xlen}cheri"

so that _qemu_arch_suffix is still set.

I think that's not even needed here. I've been running CHERI-Linux without that flag and it picks the correct QEMU's suffix

[heshamelmatary]

Can you place this in the qemu options init instead?

It just needs to be updated to use xtarget.is_experimental_cheri093_std(self.config) instead of just checking the command line flag.

That's what I tried first thing, but QemuOptions doesn't have config eg:

AttributeError: 'QemuOptions' object has no attribute 'config'

[heshamelmatary]

Can you place this in the qemu options init instead?
It just needs to be updated to use xtarget.is_experimental_cheri093_std(self.config) instead of just checking the command line flag.
And yes we can use the generic CPU instead of a730

If the problem is that the config argument is not available there we could probably just add it.

Yeah that was the issue. I just added it now (in the last push) as an argument if that's what you meant?