Create basic BR2_EXTERNAL, with a twist

Initial defconfig is based on Buildroot qemu_x86_64_defconfig, with a
Bootlin pre-built toolchain and a very basic qemu.sh script, generated
by a local post-image.sh, for `make run`.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

.gitignore

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+*~
+.gdb_history
+/.ccache
+/dl
+/output*
+/local.mk

.gitmodules

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+[submodule "buildroot"]
+	path = buildroot
+	url = https://github.com/buildroot/buildroot.git

Makefile

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+export BR2_EXTERNAL := $(CURDIR)
+export PATH         := $(CURDIR)/bin:$(PATH)
+
+ARCH ?= $(shell uname -m)
+O    ?= $(CURDIR)/output
+
+config := $(O)/.config
+bmake   = $(MAKE) -C buildroot O=$(O) $1
+
+
+all: $(config) buildroot/Makefile
+	@+$(call bmake,$@)
+
+$(config):
+	@+$(call bmake,list-defconfigs)
+	@echo "ERROR: No configuration selected."
+	@echo "Please choose a configuration from the list above by running"
+	@echo "'make <board>_defconfig' before building an image."
+	@exit 1
+
+%: buildroot/Makefile
+	@+$(call bmake,$@)
+
+buildroot/Makefile:
+	@git submodule update --init
+
+run:
+	@echo "Starting Qemu  ::  Ctrl-a x -- exit | Ctrl-a c -- toggle console/monitor"
+	@(cd $(O)/images && ./qemu.sh)
+

board/common/post-image.sh

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+#!/bin/sh
+
+# shellcheck disable=SC1090
+. "$BR2_CONFIG" 2>/dev/null
+
+cat <<-EOF >"$BINARIES_DIR/qemu.sh"
+	#!/bin/sh
+	line=\$(stty -g)
+	stty raw
+	qemu-system-x86_64 -M pc -cpu kvm64 -enable-kvm -nographic		\\
+	    -kernel bzImage -append "rootwait root=/dev/vda console=ttyS0"	\\
+	    -drive file=rootfs.ext2,if=virtio,format=raw			\\
+	    -net nic,model=virtio -net user
+	stty "\$line"
+EOF
+chmod +x "$BINARIES_DIR/qemu.sh"

configs/x86_defconfig

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+# Architecture
+BR2_x86_64=y
+BR2_x86_corei7=y
+BR2_DL_DIR="$(BR2_EXTERNAL_INFIX_PATH)/dl"
+BR2_CCACHE=y
+BR2_CCACHE_DIR="$(BR2_EXTERNAL_INFIX_PATH)/.ccache"
+BR2_ENABLE_DEBUG=y
+BR2_GLOBAL_PATCH_DIR="$(BR2_EXTERNAL_INFIX_PATH)/patches"
+BR2_TOOLCHAIN_EXTERNAL=y
+BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_X86_64_CORE_I7_UCLIBC_BLEEDING_EDGE=y
+
+# System
+BR2_SYSTEM_DHCP="eth0"
+BR2_TARGET_GENERIC_HOSTNAME="infix"
+BR2_TARGET_GENERIC_ISSUE="Inf/IX by KernelKit"
+
+# Filesystem
+BR2_TARGET_ROOTFS_EXT2=y
+# BR2_TARGET_ROOTFS_TAR is not set
+
+# Image
+BR2_ROOTFS_POST_BUILD_SCRIPT="board/qemu/x86_64/post-build.sh"
+
+# Image
+BR2_ROOTFS_POST_IMAGE_SCRIPT="board/qemu/post-image.sh $(BR2_EXTERNAL_INFIX_PATH)/board/common/post-image.sh"
+BR2_ROOTFS_POST_SCRIPT_ARGS="$(BR2_DEFCONFIG)"
+
+# Linux headers same as kernel
+BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_5_15=y
+
+# Kernel
+BR2_LINUX_KERNEL=y
+BR2_LINUX_KERNEL_CUSTOM_VERSION=y
+BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="5.15.18"
+BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
+BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="board/qemu/x86_64/linux.config"
+BR2_LINUX_KERNEL_NEEDS_HOST_LIBELF=y
+
+# host-qemu for gitlab testing
+#BR2_PACKAGE_HOST_QEMU=y
+#BR2_PACKAGE_HOST_QEMU_SYSTEM_MODE=y

external.desc

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+name: INFIX
+desc: Inf/IX by KernelKit