fix(hal): boot aarch64 to the serial console in QEMU virt - #140
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The aarch64 _start faulted before reaching Rust: (1) it set SCTLR_EL1.M to enable the MMU without ever installing a TTBR0_EL1 translation table, so the next instruction fetch took a level-1 translation abort; (2) it never enabled FP/SIMD, so the first NEON instruction emitted by Rust codegen (memcpy/formatting) trapped with ESR EC=0x07 and spun in the stub vector table. Fix both in the boot stub: defer the MMU (run with flat physical addressing until an identity page table is built — sufficient for the console + init path) and set CPACR_EL1.FPEN=0b11 before calling kernel_main. The aarch64 kernel now boots in 'qemu-system-aarch64 -M virt' and prints: [ONCRIX/aarch64] Kernel booting... [ONCRIX/aarch64] PL011 UART initialized (115200 8N1) [ONCRIX/aarch64] Heap initialized (16 MiB) x86_64 is unaffected (aarch64-only boot stub).
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The aarch64
_startfaulted before reaching Rust:SCTLR_EL1.M(MMU enable) without ever installing aTTBR0_EL1translation table → the next instruction fetch took a level-1 translation abort (ESR 0x86000005, verified viaqemu -d int).Fix both in the boot stub: defer the MMU (flat physical addressing until an identity page table is built — enough for console + init) and set
CPACR_EL1.FPEN=0b11beforekernel_main.Verified —
qemu-system-aarch64 -M virt -cpu cortex-a72 -kernel …now prints:First actual runtime execution of the cross-arch kernel. x86_64 unaffected (aarch64-only boot stub).