Two more defects making Pi 3 boot silently:
1. The kernel8.img that ships in the Pi OS armhf boot partition is a
gzip-compressed PE-COFF Image (first 4 bytes 0x1f8b0800). QEMU's
`-kernel` does NOT auto-decompress; it tries to execute the gzip
header as ARM code and the CPU faults immediately. Result: zero
bytes on ttyAMA0, simulator looks dead. Switch the asset_id to a
pre-decompressed kernel (24 MiB raw vs 9.7 MiB gzipped) so QEMU
gets a valid Image to boot.
2. Even with a real kernel, the original cmdline `console=ttyAMA0`
alone wasn't enough — the kernel can't initialise the BCM2837
PL011 UART early enough for `printk` to reach the serial console
under QEMU's bare-metal boot (no Pi firmware to set it up
beforehand). Adding `earlycon=pl011,mmio32,0x3f201000` makes the
kernel program the UART itself in the early boot path.
Verified: boot output starts streaming within 100 ms of QEMU
launch instead of never.
The cmdline also locks the baud rate at 115200 to match the agetty
drop-in created by scripts/configure-pi3-autologin.sh.
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