Generate MIPS architecture assembly code on a X86 machine

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Understanding the Basics

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From the wiki entry of MIPS architecture, it is described as,

MIPS (originally an acronym for Microprocessor without Interlocked Pipeline Stages) is a reduced instruction set computer (RISC) instruction set (ISA) developed by MIPS Technologies (formerly MIPS Computer Systems, Inc.).

From the wiki entry of the x86-64, it is described as,

x86-64 (also known as x64, x86_64 and AMD64) is the 64-bit version of the x86 instruction set.

So as per the arch output in the question, it is evident that I have a x86_64 machine and I try to produce the MIPS architecture specific code after running gcc compiler.

This is similar to trying and running a diesel car on a petrol engine. No matter how hard we try, without tweaking the gas engine, we could not run the diesel car on a petrol engine.

To describe it in a technical manner, gcc can produce assembly code for a large number of architectures, include MIPS. But what architecture a given gcc instance targets is decided when gcc itself is compiled. The precompiled binary you will find in an Ubuntu system knows about x86 (possibly both 32-bit and 64-bit modes) but not MIPS.

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How to compile a C program to MIPS assembly code

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Again quoting from the same answer, compiling gcc with a target architecture distinct from the architecture on which gcc itself will be running is known as preparing a cross-compilation toolchain. Or in layman's terms, this cross compilation toolchain is similar to tweaking the petrol engine to run the diesel car.

However, setting up a cross-compilation toolchain is quite a bit of work, so rather than describe how to set that up, I will describe how to install a native MIPS compiler into a MIPS virtual machine. This involves the additional steps of setting up an emulator for the VM and installing an OS into that environment, but will allow you to use a pre-built native compiler rather than compiling a cross compiler.

We will be first installing qemu to make our system run some virtualized operating systems. Again there are several approaches like installing some cross compiled tool chain as discussed here and using a buildroot as suggested in the answer that I earlier linked.

• Download the tar ball of qemu from here.

• After downloading the tar ball, run the following commands.

   bzip2 -d qe*
   tar -xvf qe*
   ./configure
   make
   make install
  

• Now, after installing qemu on the machine, I tried several methods of netboot for the debian OS as suggested over here and here. But unfortunately I was not able to perform the debian OS installation using the netboot because the correct mirrors were not available.

I got an image for debian which targets MIPS architecture from here and I downloaded the kernel and qemu image and from the above link and performed the below steps.

• I started the qemu as below.

  qemu-system-mips -M malta -kernel vmlinux-2.6.32-5-4kc-malta -hda 
  debian_squeeze_mips_standard.qcow2 -append "root=/dev/sda1 console=tty0"
  

• After the debian system came up, I installed the gcc compiler as below.

  apt-get update && apt-get upgrade
  apt-get install build-essential
  

Now, I have a perfectly working native gcc compiler inside the MIPS debian virtual machine on qemu, which compiles my C program to MIPS specific assembly code.

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Testing

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Inside my debian machine, I just put in a sample C hello world program and saved it as hello.c as below.

#include<stdio.h>
int main()
{
    printf("Hello World");
}

To generate MIPS architecture code for my hello.c program, I ran the C program using the gcc compiler as,

gcc -O2 -S -c hello.c

The above command generated a hello.s file which generated my MIPS architecture code.

    .file   1 "hello.c"
    .section .mdebug.abi32
    .previous
    .gnu_attribute 4, 1
    .abicalls
    .section    .rodata.str1.4,"aMS",@progbits,1
    .align  2
$LC0:
    .ascii  "Hello World\000"
    .text
    .align  2
    .globl  main
    .set    nomips16
    .ent    main
    .type   main, @function
main:
    .frame  $sp,0,$31       # vars= 0, regs= 0/0, args= 0, gp= 0
    .mask   0x00000000,0
    .fmask  0x00000000,0
    .set    noreorder
    .set    nomacro

    lui $28,%hi(__gnu_local_gp)
    addiu   $28,$28,%lo(__gnu_local_gp)
    lui $4,%hi($LC0)
    lw  $25,%call16(printf)($28)
    nop
    jr  $25
    addiu   $4,$4,%lo($LC0)

    .set    macro
    .set    reorder
    .end    main
    .size   main, .-main
    .ident  "GCC: (Debian 4.4.5-8) 4.4.5"

But how will I know if the above generated code is MIPS assembly code?

The arch command's output will tell the machine's architecture. In my debian machine, it produces the output as mips and I also do not have any binutils or cross-compiler tool chains installed in the machine.

So, the generated assembly code is MIPS specific.

You need a cross toolchain, gcc (+binutils) which run on x86_64 but output mips binaries.

You can try to build it yourself from scratch (google for examples: build cross toolchain) or download a pre-built one (like from Codesourcery)

Or you may build your own with the help of some tool like crosstool-ng

Also systems like buildroot build (or download) their own cross toolchain (I guess also OpenWRT).

The emdebian project has done some work on cross toolchains.

As these packages suffer from bit rot quite heavily, I'd inquire about the current status with the emdebian project, either via mailing list or IRC.