Set 8250.nr_uarts when running x86 kernels

Author: gsingh93

Makefile

@@ -392,7 +392,10 @@ endif
 
 ifeq ($(ARCH),x86_64)
   QEMU_BIN := qemu-system-x86_64
-  QEMU_KERNEL_CMDLINE += console=ttyS0 kpti no5lvl
+
+  # 8250.nr_uarts=1 is needed because some Android kernels set
+  # `CONFIG_SERIAL_8250_RUNTIME_UARTS` to zero
+  QEMU_KERNEL_CMDLINE += console=ttyS0 kpti no5lvl 8250.nr_uarts=1
 
   QEMU_ARGS += -cpu kvm64,+smep,+smap
 

config/config.fragment

@@ -92,3 +92,8 @@ CONFIG_TRACING=y
 
 # Allow lvl5 paging
 CONFIG_X86_5LEVEL=y
+
+# Some ACK kernels set this to zero. Technically we don't need it because we
+# also set it in the kernel command line, but it helps if someone wants to use
+# our prebuilt kernels and run them manually
+CONFIG_SERIAL_8250_RUNTIME_UARTS=4