developersguide:crosscompiling [Wiki]

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====== Cross-compiling MINIX 3 ======

<div round info>
**Note:**

This is for cross-compiling MINIX from another Unix-like system. To build MINIX from within MINIX, [[.:rebuildingsystem|check this page]] instead.
</div>

Cross-compilation is the act of building MINIX from another operating system. Since MINIX now uses the build.sh framework from NetBSD, cross-compilation should work on most mainstream UNIX-compatible systems. A build compatibility table is available at the end of this document.

===== Install dependencies =====

Before attempting to cross-compile MINIX, you need a working C toolchain, Git and some additional software on your host platform.

For Debian-based operating systems, run the following command as super-user:

<code>
# apt-get install build-essential curl git zlibc zlib1g zlib1g-dev
</code>

**Note**: Also on Ubuntu, if you get an error stating that "'/lib/cpp' fails sanity check", you need to install the GNU C++ compiler:

<code>
$ sudo apt-get install g++
</code>

**Note**: On FreeBSD and Minix ([[developersguide:minixonarm#building_minix_arm |compiling for ARM on x86, e.g.)]], if you get a message along the lines of "Skipping image creation: missing tool 'mcopy'", please install the emulators/mtools package.

===== Getting the sources =====

Once the required tools are installed, the next step is to obtain the sources. Run the following commands in a terminal:

<code>
$ mkdir minix
$ cd minix
$ git clone git://git.minix3.org/minix src
$ cd src
</code>

NOTE: The releasetools script will generate object files and put them //outside// the source directory; i.e., if you've cloned to ~/minix/src/ and build from there, things will start showing up in ~/minix/ as an artifact of the build process.

===== Cross-building for x86 =====

It's time to build MINIX itself. There are some wrapper scripts that will build ready-to-boot images from scratch (i.e. just the minix source tree) for either x86 or ARM. These scripts produce a lot of output and will take a while to complete the first time - a cross-toolchain based on LLVM is built from scratch.

<code>
$ bash ./releasetools/x86_hdimage.sh 
[..]
Writing Minix filesystem images
 - ROOT
 - USR
 - HOME
Part     First         Last         Base      Size       Kb
  0      0/000/00     0/000/07         0         8        4
  1      0/000/08    64/000/07         8    131072    65536
  2     64/000/08  1856/000/07    131080   3670016  1835008
  3   1856/000/08  1984/000/07   3801096    262144   131072
To boot this image on kvm:
[..]
</code>

A command line for running the result in a KVM virtual machine is printed at the end of the process.

===== Cross-building for ARM =====

A similar procedure exists for ARM. Please see [[.:MinixOnARM]] for much more information.

===== Using build.sh directly =====

Please refer to NetBSD's documentation on build.sh for details.

From a source directory:

<code>
$ sh build.sh -mi386 -O ../build tools
</code>

Please note that by default, the build.sh script will output the built objects to ''/usr/obj'', so make sure it exists. Alternatively, use as above the "-O" option to redirect the output to somewhere else. When this process is completed, you'll have a ../build/tooldir.<something> directory. The <something> is roughly equivalent to

<code>
$ echo ''uname -s''-''uname -r''-''uname -m''
</code>

Among the tools that are built are ''gcc'', ''binutils'', and ''gmake''. The sources for these tools are not provided by us. Instead, they are downloaded on-the-fly as tarballs from the minix webserver

===== Building world =====

The next step is to actually build MINIX:

<code>
$ sh build.sh -mi386 -O ../build -U distribution
</code>

This process will create a ../build/destdir.i386 directory that holds the built distribution of MINIX. 

Other useful options for qemu are ''-monitor telnet::4444,server,nowait'' (to access some interesting internal state by telnet) and ''-serial stdio'' - for convenient debug output over 'serial.'

===== Compiling things without build.sh =====

To run make in the cross-environment, i.e. to rebuild a tool (host target) or minix item (minix target), without running the full build.sh procedure all over again, use nbmake-i386, a make wrapper that sets all the right environment. First expand your $PATH to include it:

<code>
$ PATH=$PATH:OBJDIR/tooldir.OS-VERSION-ARCH/bin/
$ cd SRCDIR/tools
$ nbmake-i386 clean
$ nbmake-i386
</code>
will rebuild all the tools. After that you can e.g.

<code>
$ cd zic
$ nbmake-i386 clean
$ nbmake-i386
</code>

to just rebuild zic. As you can tell if you set MAKEVERBOSE=2, tools/zic/ will invoke cc (to run on the host platform), whereas nbmake-i386 will invoke i486--netbsdelf-gcc from your tools dir if you run it in usr.sbin/zic/, so a Minix-targeted binary is produced.

===== Caveats =====

The ''build.sh'' is tailored towards NetBSD and as such not all features make sense for MINIX. For example, we don't have a kernel configuration file. Also, you can't use ''build.sh'' for native builds on MINIX at the time of this writing. You can consult ''build.sh'''s documentation by invoking:

<code>
$ sh build.sh
</code>

But know that not all operations and options are supported. For example, we only support the ''distribution'' build operation. You can't generate iso images with the ''build.sh'' script.

==== Build flags for build.sh ====

It is possible to tweak the build using build flags. Here are some you might find useful.

|Option name |value |example |Description |
|COPTS |c flags |COPTS=-g |**c** compiler **opt**ions |




==== Build flags for nbmake ====

It is also possible to tweak when building separate components using nbmake-i386

| Option name | value | example       | Description                      |
| MAKEVERBOSE | [1]   | MAKEVERBOSE=2 | Instruct make to be more verbose |


==== Mounting a MINIX disk image on Linux ====

1. Load the loop kernel module, or adapt kernel command line:

<code>
$ modprobe loop max_part=15
</code>

or add to your kernel commandline : **max_part=15**

2. Setup a loopback device to point to your disk image:

<code>
$ losetup /dev/loop0 minix.img
</code>

3. (Optional) list the available partitions:

<code>
$ dmesg | tail
</code>

or use

<code>
$ ls /dev/loop0*
</code>

4. Mount the desired partition somewhere

<code>
$ mount /dev/loop0p5 /mnt
</code>

===== Build compatibility =====

^  Host platform                     ^ Version  ^  Buildable MINIX architectures ^ Version ^ Updated  |
| Ubuntu x86 32-bit                  | 14.04    | x86 32-bit / ARMv7             | 3.4.0rc | 2016-02  |
| Ubuntu x86 64-bit                  | 14.04    | x86 32-bit / ARMv7             | 3.4.0rc | 2016-02  |
| Arch Linux x86 32-bit              |          | x86 32-bit                     | 3.2.1   | 2013-08  |
| Arch Linux x86 64-bit              |          | x86 32-bit / ARMv7             | 3.2.1   | 2013-08  |
| Mac OS X Lion x86 64-bit           |          | x86 32-bit / ARMv7             | 3.2.1   | 2013-08  |
| Mac OS X Maverick x86 64-bit       |          | x86 32-bit / ARMv7             | 3.3.0   | 2014-10  |
| FreeBSD x86 32-bit                 | 10-CURR. | x86 32-bit / ARMv7             | 3.2.1   | 2013-08  |
| FreeBSD x86 64-bit                 | 10-CURR. | x86 32-bit / ARMv7             | 3.2.1   | 2013-08  |
| Windows Subsystem for Linux 64-bit | 10.14393 | x86 32-bit / ARMv7             | 3.4.0rc | 2016-08  |
| Debian x86 32-bit                  | 8.8.0    | x86 32-bit                     | 3.3.0   | 2017-05  |
| Debian x86 64-bit ((Apply [[https://github.com/Stichting-MINIX-Research-Foundation/minix/pull/301|this]] patch))                 | 10.9.0   | x86 32-bit / ARMv7             | 3.4.0rc | 2021-03  |
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