Native MIPS Systems

The MIPS architecture is unusual in that it was designed for desktop computers, is now overwhelmingly used for embedded systems, but can still occasionally be found in desktops or small servers. The only comparable architecture is ARM, which is the platform of choice for a multitude of mobile phones, tablets etc.

Like almost all computers, MIPS-based systems will contain an internal loader, usually in flash memory. However there are three basic categories of system:

• Those that boot an operating system from internal flash, such as the Linksys/Cisco WRT54G [1].

• Those that boot an operating system from a conventional disc, connected via IDE, SCSI or USB, such as an SGI server or workstation, or a Cobalt/Sun Qube or Raq.

• Those running as guests using an emulator such as Qemu on a general-purpose computer.

In any of these cases it is necessary to be able to install a general-purpose operating system such as Linux in order to be able to run development tools. This writer (MarkMLl) favours Debian, since he finds that using it results in a very similar system on a wide range of hardware (x86, SPARC, PPC, MIPS, ARM, zSeries, 68K).

If you intend to build Lazarus, make sure you have at least 512Mb memory (RAM + swap) available.

FPC Implementations for MIPS

As of 2011 there are two implementations of FPC for the MIPS architecture, both targeting Linux.

• A fork of the mainline compiler at 2.0.0 by David Zhang. Now deprecated due to mainline integration.

• An ongoing effort to reconcile this with the mainline project, in SVN trunk and partially completed in 2.7.x.

David Zhang's Compiler

The "unofficial" MIPS compiler at [2] was written by David Zhang (possibly [3]) and is licensed under GPL Version 2, it cites but does not include the COPYING.FPC file. The compiler appears to have been originally based on the SPARC port, and there are significant differences between it and the mainline sources. It is discussed for historical interest, and as reference until the mainline compiler is at least as complete and robust.

There are .zip files of both sources and a minimal executable at Sourceforge (link above). The sources are basically a complete reimplementation of fpcsrc/compiler/mips based on FPC 2.0.0, the compiler targets mipsel and is described as being operational on Qemu but not yet supporting shared libraries.

Since this is specifically a little-endian compiler it should presumably be compatible with Linux on a MIPS-based Qube or Raq, or with the Chinese "Loongson" processor of fable. It will not be compatible with SGI MIPS systems, which are big-endian.

There is a system library bundled with the compiler, but no indication of how far the compiler is capable of handling the remainder of the standard libraries. The released files may be downloaded from:

• http://sourceforge.net/projects/fpc-mips/files/fpc-mips/0.90/fpc_mips_bin_090.zip/download

This comprises the binary compiler pp_mipsel32. It successfully compiles a minimal test program which appears to run.

• http://sourceforge.net/projects/fpc-mips/files/fpc-mips/0.90/fpc_mips_all_090a.zip/download

This is both source and binary, dumped into a single directory which appears to correspond to the standard fpc_200/compiler, i.e. there's no separate compiler/mips directory; it also partially reimplements some standard libraries etc.

Mainline MIPS Port

This is part of the trunk development files, but does not yet appear in standard releases; i.e. it's only available via an svn download.

The host is assumed to be a non-MIPS system, for example x86 running Linux (e.g. Debian "Squeeze"). It needs a copy of binutils, and it is probably expedient to make this the same version as is running natively, i.e. 2.20.1 in the above case, downloaded from [4]. In any event, no version older than 2.18 will work since symbolic register names are a prerequisite.

Build and install cross-binutils:

tar xjf binutils-2.20.1.tar.bz2
cd binutils-2.20.1
./configure --prefix=/usr/local/mipsel-linux mipsel-linux-gnu
make
sudo make install
sudo ln -s /usr/local/mipsel-linux/bin/as /usr/local/bin/mipsel-linux-as
sudo ln -s /usr/local/mipsel-linux/bin/ld /usr/local/bin/mipsel-linux-ld
sudo ln -s /usr/local/mipsel-linux/bin/ar /usr/local/bin/mipsel-linux-ar
sudo ln -s /usr/local/mipsel-linux/bin/objdump /usr/local/bin/mipsel-linux-objdump
sudo ln -s /usr/local/mipsel-linux/bin/objcopy /usr/local/bin/mipsel-linux-objcopy
sudo ln -s /usr/local/mipsel-linux/bin/strip /usr/local/bin/mipsel-linux-strip
mipsel-linux-ld -V

Particularly if working with the trunk sources, consider doing the same for a different CPU (e.g. powerpc-linux-gnu) so as not to be caught out if they won't build due to a temporary inconsistency.

Build a compiler which runs on the host but targets mipsel, note debug options which are needed later:

cd /usr/local/src/fpc-trunk
export PP=
make "OPT=-O- -g" -C compiler mipsel
mv compiler/ppcmipsel compiler/ppcXmipsel

Renaming the compiler prevents it from being deleted by make clean etc., consider extending that OPT setting with -dEXTDEBUG.

export PP=/usr/local/src/fpc-trunk/fpc/compiler/ppcXmipsel
make CPU_TARGET=mipsel OS_TARGET=linux compiler
make CPU_TARGET=mipsel OS_TARGET=linux rtl

Move the newly-generated compiler and the RTL units to the target system, which should now be able to do a full build.

Stall point

As of October 2012 there are still some code-generation tests failing.

To be continued (hopefully :-)

As a general point, there's some useful thoughts on binary disassembly at [5] for situations where IDA or equivalent aren't available.

Big-endian subarchitecture

Working notes, no permanent links.

This is a highly-experimental investigation of how much work it would take to port the existing little-endian compiler (mipsel) to big-endian architectures. Note that the GNU triplet is mips-linux-gnu, there is no such thing as mipsel-linux-gnu etc.

Build and install cross-binutils:

tar xjf binutils-2.20.1.tar.bz2
cd binutils-2.20.1
./configure --prefix=/usr/local/mips-linux mips-linux-gnu
make
sudo make install
sudo ln -s /usr/local/mips-linux/bin/as /usr/local/bin/mips-linux-as
sudo ln -s /usr/local/mips-linux/bin/ld /usr/local/bin/mips-linux-ld
sudo ln -s /usr/local/mips-linux/bin/ar /usr/local/bin/mips-linux-ar
sudo ln -s /usr/local/mips-linux/bin/objdump /usr/local/bin/mips-linux-objdump
sudo ln -s /usr/local/mips-linux/bin/objcopy /usr/local/bin/mips-linux-objcopy
sudo ln -s /usr/local/mips-linux/bin/strip /usr/local/bin/mips-linux-strip
mips-linux-ld -V

Build a compiler which runs on the host but targets mipsel, note debug options which are needed later:

cd /usr/local/src/fpc-trunk
export PP=
make "OPT=-O- -g" -C compiler mips
mv compiler/ppcmips compiler/ppcXmips

For my own reference, actually using /usr/local/src/fpc/zhang/fpc-trunk/fpc

export PP=/usr/local/src/fpc-trunk/fpc/compiler/ppcXmips
# make CPU_TARGET=mips OS_TARGET=linux compiler
make CPU_TARGET=mips OS_TARGET=linux rtl

Are the compiler and RTL in the wrong order there? If I build the RTL first then the compiler I get

file compiler/ppcmips compiler/ppcmips: ELF 32-bit MSB executable, MIPS, MIPS-II version 1 (SYSV), statically linked, stripped

file rtl/units/mips-linux/system.o rtl/units/mips-linux/system.o: ELF 32-bit MSB relocatable, MIPS, MIPS-II version 1 (SYSV), not stripped