some more docs, retore full Linux configs, wont touch that now

README.adoc

@@ -193,7 +193,24 @@ We tend to support the following Ubuntu host versions at least:
 
 ==== About the QEMU Buildroot setup
 
-link:https://en.wikipedia.org/wiki/Buildroot[] is a set of `make` scripts that downloads everything from source
+link:https://en.wikipedia.org/wiki/Buildroot[] is a set of `make` scripts that downloads from source and compiles compatible versions of:
+
+* GCC
+* Linux kernel
+* glibc
+* BusyBox
+
+It therefore produces a pristine, blob-less and debuggable setup.
+
+The price that you pay is that the first build takes a while, but it is well worth it.
+
+link:https://en.wikipedia.org/wiki/QEMU[QEMU] is a system simulator: it simulates a CPU and devices such as interrupt handlers, timers, UART, screen, keyboard, etc.
+
+QEMU is the leading cross arch system simulator as of 2018. It is even the default Android simulator that developers get with Android Studio 3 to develop apps without real hardware.
+
+QEMU is also supported by Buildroot in-tree, see e.g.: https://github.com/buildroot/buildroot/blob/2018.05/configs/qemu_aarch64_virt_defconfig
+
+All of this makes QEMU the natural choice of system simulator.
 
 === gem5 Buildroot setup
 
@@ -2574,9 +2591,9 @@ We also have one letter shorthand names for the architectures and `--arch` optio
 
 ....
 # aarch64
-./run --arch aarch64
+./run -a A
 # arm
-./run --arch arm
+./run -a a
 # x86_64
 ./run -a x
 ....
@@ -9665,10 +9682,10 @@ This directory has the following structure:
 
 Every directory inside it is a Buildroot package.
 
-Those packages get automatically added to Buildroot's `BR2_EXTERNAL` so you just need to turn them on during build, e.g.:
+Those packages get automatically added to Buildroot's `BR2_EXTERNAL`, so all you need to do is to turn them on during build, e.g.:
 
 ....
-BR2_SAMPLE_PACKAGE=y
+./build --buildroot-config BR2_SAMPLE_PACKAGE=y
 ....
 
 ==== patches

build

@@ -12,6 +12,7 @@ import re
 import common
 
 defaults = {
+    'buildroot_bare_kernel': False,
     'buildroot_config': [],
     'buildroot_config_fragment': [],
     'initramfs': False,
@@ -146,7 +147,7 @@ def main(args, extra_args=None):
                 default_kernel_config_fragments = []
             else:
                 kernel_config_fragment_dir = os.path.join(common.root_dir, 'kernel_config')
-                default_kernel_config_fragments = ['min']
+                default_kernel_config_fragments = ['min', 'default']
                 if args.linux_reconfigure:
                     # https://stackoverflow.com/questions/49260466/why-when-i-change-br2-linux-kernel-custom-config-file-and-run-make-linux-reconfi
                     pathlib.Path(os.path.join(kernel_config_fragment_dir, 'min')).touch()

kernel_config/default

@@ -1,28 +1,16 @@
+# Misc.
 CONFIG_BLK_DEV_INITRD=y
-CONFIG_STRICT_DEVMEM=n
+CONFIG_DEBUG_FS=y
 CONFIG_DYNAMIC_DEBUG=y
 CONFIG_MODULE_SRCVERSION_ALL=y
 CONFIG_OVERLAY_FS=y
+CONFIG_STRICT_DEVMEM=n
 
 # GDB debugging.
-CONFIG_DEBUG_FS=y
 CONFIG_DEBUG_INFO=y
 CONFIG_DEBUG_KERNEL=y
 CONFIG_GDB_SCRIPTS=y
 
-# Non-static variables show up on /proc/kallsyms
-# https://stackoverflow.com/questions/20196636/does-kallsyms-have-all-the-symbol-of-kernel-functions/44614878#44614878
-CONFIG_KALLSYMS_ALL=y
-
-# /proc/config.gz
-CONFIG_IKCONFIG=y
-CONFIG_IKCONFIG_PROC=y
-
-# TODO make example.
-# This seems to allow userspace to create arbitrary configuration trees,
-# which kernel modules can then read and interpret.
-CONFIG_CONFIGFS_FS=y
-
 # KGDB
 CONFIG_CONSOLE_POLL=y
 CONFIG_KDB_CONTINUE_CATASTROPHIC=0
@@ -38,6 +26,19 @@ CONFIG_MAGIC_SYSRQ=y
 CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE=0x1
 CONFIG_SERIAL_KGDB_NMI=n
 
+# Non-static variables show up on /proc/kallsyms
+# https://stackoverflow.com/questions/20196636/does-kallsyms-have-all-the-symbol-of-kernel-functions/44614878#44614878
+CONFIG_KALLSYMS_ALL=y
+
+# /proc/config.gz
+CONFIG_IKCONFIG=y
+CONFIG_IKCONFIG_PROC=y
+
+# TODO make example.
+# This seems to allow userspace to create arbitrary configuration trees,
+# which kernel modules can then read and interpret.
+CONFIG_CONFIGFS_FS=y
+
 # Module.symvers in kernel tree and modules tree contains CRC of signatures.
 # TODO: I think the CRC are stored in the built kernel and module, and checked
 # at insmod, but bgrep did not find it in kernel image.

kernel_config/min

@@ -1,4 +1,4 @@
-# This file contains only configs which are required to boot all configurations.
+# This file contains only configs which are required to boot all configurations and get a shell.
 
 ## gem5 x86