ARM

README.md

@@ -1,6 +1,6 @@
 # Linux Kernel Module Cheat
 
-Run one command, get into QEMU Buildroot BusyBox with several minimal Linux kernel 4.9 module example tutorials with GDB debug support. Tested in Ubuntu 14.04 - 16.10 hosts.
+Run one command, get into QEMU Buildroot BusyBox with several minimal Linux kernel 4.9 module example tutorials with GDB debug support. x86 and ARM guests supported. Tested in Ubuntu 14.04 - 16.10 hosts.
 
 Usage:
 
@@ -176,6 +176,37 @@ And then tell GDB where the module was loaded with:
     Ctrl + C
     add-symbol-file ../kernel_module-1.0/fops.ko 0xfffffffa00000000
 
+## ARM
+
+The portability of the kernel and toolchains is amazing.
+
+If you already have an x86 build present, first:
+
+    cd buildroot
+    mv output output.x86~
+
+First ARM build:
+
+    ./run -a arm
+
+Run without build:
+
+    ./runqemu -a arm
+
+Debug:
+
+    ./runqemu -a arm -d
+    # On another terminal.
+    ./rungdb -a arm
+
+ARM TODOs:
+
+-   only managed to run in the terminal interface (but weirdly an blank QEMU window is still opened)
+-   Ctrl + C kills the emulator, not sent to guest. See:
+    - <https://github.com/cloudius-systems/osv/issues/49>
+    - <https://unix.stackexchange.com/questions/167165/how-to-pass-ctrl-c-in-qemu>
+-   `fops.ko`, `printf a >fops` crashes with `BUG: recent printk recursion!`
+
 ## Table of contents
 
 1.  [Introduction](introduction.md)

kernel_module/external.mk

@@ -9,7 +9,14 @@ KERNEL_MODULE_SITE = $(BR2_EXTERNAL_KERNEL_MODULE_PATH)
 KERNEL_MODULE_SITE_METHOD = local
 
 define KERNEL_MODULE_BUILD_CMDS
-	$(MAKE) -C '$(@D)' LINUX_DIR='$(LINUX_DIR)' PWD='$(@D)' CC='$(TARGET_CC)' LD='$(TARGET_LD)'
+	$(MAKE) \
+	  -C '$(@D)' \
+	  ARCH='$(KERNEL_ARCH)' \
+	  CC='$(TARGET_CC)' \
+	  CROSS_COMPILE='$(TARGET_CROSS)' \
+	  LD='$(TARGET_LD)' \
+	  LINUX_DIR='$(LINUX_DIR)' \
+	  PWD='$(@D)'
 endef
 
 define KERNEL_MODULE_INSTALL_TARGET_CMDS

kernel_module/test/myrmmod.c

@@ -15,7 +15,7 @@ int main(int argc, char **argv) {
 		return EXIT_FAILURE;
 	}
     if (delete_module(argv[1], O_NONBLOCK) != 0) {
-        perror("delete_modul");
+        perror("delete_module");
         return EXIT_FAILURE;
     }
     return EXIT_SUCCESS;

run

@@ -1,7 +1,25 @@
 #!/usr/bin/env bash
 set -e
 cd buildroot
-make BR2_EXTERNAL="$(pwd)/../kernel_module" qemu_x86_64_defconfig
+arch='x86_64'
+while getopts a: OPT; do
+  case "$OPT" in
+    a)
+      arch=$OPTARG
+      ;;
+  esac
+done
+case "$arch" in
+  x86_64)
+    defconfig=qemu_x86_64_defconfig
+    ;;
+  arm)
+    # qemu_arm_vexpress_defconfig required a newer QEMU than 2.0.0 on a Ubuntu host.
+    # so let's stick to versatile for now.
+    defconfig=qemu_arm_versatile_defconfig
+    ;;
+esac
+make BR2_EXTERNAL="$(pwd)/../kernel_module" "$defconfig"
 # Can't get rid of this for now.
 # http://stackoverflow.com/questions/44078245/is-it-possible-to-use-config-fragments-with-buildroots-config
 cat ../buildroot_config_fragment >> .config

rungdb

@@ -1,22 +1,51 @@
 #!/usr/bin/env bash
+
+set -e
+
+arch=x86_64
+while getopts a: OPT; do
+  case "$OPT" in
+    a)
+      arch=$OPTARG
+      ;;
+  esac
+done
+shift "$(($OPTIND - 1))"
 if [ "$#" -gt 0 ]; then
   brk="-ex 'break $1'"
 else
   brk=""
 fi
-gdb="$(pwd)/buildroot/output/host/usr/bin/x86_64-linux-gdb"
+
+gdb="$(pwd)/buildroot/output/host/usr/bin/${arch}-linux-gdb"
 cd buildroot/output/build/linux-*.*.*/
-cmd="$gdb \
-  -q \
-  -ex 'add-auto-load-safe-path $(pwd)' \
-  -ex 'file vmlinux' \
-  -ex 'set arch i386:x86-64:intel' \
-  -ex 'target remote localhost:1234' \
-  $brk \
-  -ex 'continue' \
-  -ex 'disconnect' \
-  -ex 'set arch i386:x86-64' \
-  -ex 'target remote localhost:1234' \
-  -ex 'lx-symbols ../kernel_module-1.0/'
-"
+case "$arch" in
+  x86_64)
+    # http://stackoverflow.com/questions/11408041/how-to-debug-the-linux-kernel-with-gdb-and-qemu/33203642#33203642
+    # http://stackoverflow.com/questions/4943857/linux-kernel-live-debugging-how-its-done-and-what-tools-are-used/42316607#42316607
+    # http://stackoverflow.com/questions/28607538/how-to-debug-linux-kernel-modules-with-qemu/44095831#44095831
+    cmd="$gdb \
+      -q \
+      -ex 'add-auto-load-safe-path $(pwd)' \
+      -ex 'file vmlinux' \
+      -ex 'set arch i386:x86-64:intel' \
+      -ex 'target remote localhost:1234' \
+      $brk \
+      -ex 'continue' \
+      -ex 'disconnect' \
+      -ex 'set arch i386:x86-64' \
+      -ex 'target remote localhost:1234' \
+      -ex 'lx-symbols ../kernel_module-1.0/'
+    "
+    ;;
+  arm)
+    cmd="$gdb \
+      -q \
+      -ex 'add-auto-load-safe-path $(pwd)' \
+      -ex 'file vmlinux' \
+      -ex 'target remote localhost:1234' \
+      -ex 'lx-symbols ../kernel_module-1.0/'
+    "
+    ;;
+esac
 eval "$cmd"

runqemu

@@ -3,12 +3,16 @@
 set -e
 
 # CLI handling.
+arch=x86_64
 debug=false
 nographic=false
 extra_append=''
 extra_flags=''
-while getopts dn OPT; do
+while getopts a:dn OPT; do
   case "$OPT" in
+    a)
+      arch=$OPTARG
+      ;;
     d)
       debug=true
       extra_flags="$extra_flags -S -s"
@@ -21,23 +25,41 @@ while getopts dn OPT; do
   esac
 done
 
-# If we turn on buildroot host QEMU some day.
-#cmd="./buildroot/output/host/usr/bin/qemu-system-x86_64 \
-cmd="qemu-system-x86_64 \
-  -M pc \
-  -append 'root=/dev/vda $extra_append' \
-  -drive file=buildroot/output/images/rootfs.ext2,if=virtio,format=raw \
-  -kernel buildroot/output/images/bzImage \
-  -m 128M \
-  -net nic,model=virtio \
-  -net user \
-  -smp 1 \
-  $extra_flags \
-;
-"
+images_dir='buildroot/output/images'
+case "$arch" in
+  x86_64)
+      # If we turn on buildroot host QEMU some day.
+      #cmd="./buildroot/output/host/usr/bin/qemu-system-x86_64 \
+      cmd="qemu-system-x86_64 \
+        -M pc \
+        -append 'root=/dev/vda $extra_append' \
+        -drive file=${images_dir}/rootfs.ext2,if=virtio,format=raw \
+        -kernel ${images_dir}/bzImage \
+        -m 128M \
+        -net nic,model=virtio \
+        -net user \
+        -smp 1 \
+        $extra_flags
+      "
+    ;;
+  arm)
+    cmd="qemu-system-arm \
+      -M versatilepb \
+      -append 'root=/dev/sda console=ttyAMA0,115200' \
+      -drive file=${images_dir}/rootfs.ext2,if=scsi,format=raw \
+      -dtb ${images_dir}/versatile-pb.dtb \
+      -kernel ${images_dir}/zImage \
+      -m 128M \
+      -net nic,model=rtl8139 \
+      -net user \
+      -serial stdio \
+      -smp 1 \
+      $extra_flags"
+    ;;
+esac
 
-if $debug && ! $nographic; then
-  eval nohup "$cmd" &>/dev/null &
+if "$debug" && ! "$nographic" && [ ! "$arch" = 'arm'  ]; then
+  eval "$cmd" &>/dev/null &
   # TODO: Ctrl +C gets sent to QEMU? Why? Does not happen if I run
   # ./rungdb manually from outside this script!!! But why?!?!
   # eval has nothing to do with it, minimized example with explicit