fix: stop advertising unimplemented Zkr in FDT ISA string#3
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The emulator CPU doesn't implement the `seed` CSR that the Zkr (cryptographic seed) extension requires, but the hardcoded ISA extension string in riscv_exts advertised it. Linux 6.18+ `arch_get_random_seed_longs` trusts the FDT, issues `csrrwi x13, seed, 0` at `start_kernel+0x68a` (before any console is initialized), and the undefined instruction trap kills the kernel before it can even complain (Oops — illegal instruction, then immediate panic). Empirical repro: boot any recent-mainline Linux kernel with Zkr detection enabled; it will oops at `random_init_early`. Confirmed in Scalar Evolution / Alpine riscv64 linux-lts 6.18.22 under this emulator. Drop zkr from the advertised extension list until the CSR is wired up. Other zk* extensions (zbkb, zbkx) stay because they're just bit-manip instructions already covered by the JIT.
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SolAstrius
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May 1, 2026
The emulator CPU doesn't implement the `seed` CSR that the Zkr (cryptographic seed) extension requires, but the hardcoded ISA extension string in riscv_exts advertised it. Linux 6.18+ `arch_get_random_seed_longs` trusts the FDT, issues `csrrwi x13, seed, 0` at `start_kernel+0x68a` (before any console is initialized), and the undefined instruction trap kills the kernel before it can even complain (Oops — illegal instruction, then immediate panic). Empirical repro: boot any recent-mainline Linux kernel with Zkr detection enabled; it will oops at `random_init_early`. Confirmed in Scalar Evolution / Alpine riscv64 linux-lts 6.18.22 under this emulator. Drop zkr from the advertised extension list until the CSR is wired up. Other zk* extensions (zbkb, zbkx) stay because they're just bit-manip instructions already covered by the JIT.
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Summary
The emulator CPU doesn't implement the `seed` CSR that the Zkr (cryptographic seed) extension requires, but the hardcoded ISA extension list in `rvvm.c` advertises it. Modern Linux kernels (6.18+) trust the FDT and call `csrrwi x13, seed, 0` from `arch_get_random_seed_longs` during `random_init_early` — before any console is initialised — and the undefined-instruction trap panics the guest immediately.
Drop `zkr` from `riscv_exts` until the CSR is wired up.
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