Building a MIPS Compiler for Windows on a Linux VM!

I’ve tried to build a cross compiler on MinGW32 before, and despite there being obvious steps on how to do it, I’ve never gotten it to work.  Now I’ve built cross compilers before so it’s not like I don’t have any clue on what I’m doing, but the problem is that Windows isn’t UNIX, and I don’t want to use Cygwin.

So that enters another fun possibility known as the Canadian Cross, which is using a machine in the middle to build a compiler.  As we all know, Linux is great for building and running GNU software, so a Linux machine to build my cross compiler would be the best.  Now the whole point of this is that I wanted to build a MIPS program to run on Dynamips.  And through a LOT of googling, I managed to find this program called CILO the cisco Linux loader.  Now as far as I can tell the people trying to port Linux the the MIPS based cisco routers (3600 and 7200) never succeed, but they did manage to leave this bootloader behind.  And compiling it was very tricky as they gave no hints on what to use.  So with a lot of trial and error I found that binutils 2.18 is the minimal version that will work as the code depends on being able to do register aliasing which isn’t present in previous versions.  Also according to this, they were using gcc 4.1.2 in their Linux port. So with some luck I did mange to get CILO to build with a cross compiler on Linux.  Which was pretty awesome to see Dynamips run a C program!

But that doesn’t help me on the Windows side.

Now the first thing that I’d normally do is install the default MinGW cross tools, but because I need ancient binutils and GCC support as newer versions not only won’t work for what I want, but won’t build older versions I tried to keep things in step.  This meant on Linux I first had to build a Linux to Windows cross compiler using binutils version 2.25.1 and GCC version 4.1.2 . Configuring and building binutils was a snap with:

./configure --target=i686-mingw32 --prefix=/usr/local/mingw32

And configuring and building gcc was also a snap with:

./configure --target=i686-mingw32 --prefix=/usr/local/mingw32 --disable-libssp

I thought I could just use a new mingwrt and w32api but that proved disastrous as the newer libs gave me this fun error on trying to link a Win32 execuatable:

undefined reference to `___chkstk_ms’

And googling that around the consensus is that your binutils, and gcc is too old, and upgrade, granpa!  But I want old software so I naturally have to just use older versions, and for gcc 4.1.2 I wanted:

  • mingwrt-3.18-mingw32-dev.tar.gz
  • w32api-3.15-1.mingw32-dev.tar.lzma

Now I could build and link and test my Linux to Windows toolchain!

Now for the crazy part.

First I need a binutils, so I configured binutils 2.18 like this:

./configure --host=i686-mingw32 --target=mips-elf --prefix=/mips

And sure enough with a little prodding I had a MIPS assembler/linker/librarian and all that fun stuff!

Next was a little (ok a LOT) more fun which was building gcc.

After about 30 aborted attempts I finally got gcc to build with this:

./configure --target=mips-elf --prefix=/mips --disable-libssp --build=i486-linux-gnu --host=i686-mingw32

The fun part of course is that during the build, gcc will want to run the cross compiler and dump it’s host machine bit types by running ‘xgcc -dumpspecs’.  Well thankfully via wine, Linux can run Win32 execuatables so I saved myself a few minutes by not having to copy over the partial compiler, and run the command, and transfer the results back.

So with a bit more hand holding on the build I finally got it to finish compiling by linking /bin/true to fix-headers . What a mission.  Now I excitedly transfered my build to my Windows host, and setup some environment variables and built the hello world cisco application, and, it worked! (well crashes the same way as the pre-built one, but it does say:

C7200 ‘default’: starting simulation (CPU0 PC=0xffffffffbfc00000), JIT disabled.
ROMMON emulation microcode.

Launching IOS image at 0x80008000…
Hello World!
Image returned to ROM.
Reset in progress…

Which is pretty cool!

I tried to merge in a make utility but that turned out to be kind of screwed up, so I just copied the cross steps from Linux, and now I can build cilo on Windows!

C7200 ‘default’: starting simulation (CPU0 PC=0xffffffffbfc00000), JIT disabled.
ROMMON emulation microcode.

Launching IOS image at 0x8000d2e4…
Error: Unable to find any valid flash! Aborting load.
Image returned to ROM.
Reset in progress…

It may not look like much, but It is running the program!  Dynamips is missing a bunch of hardware, like flash.  Or I found out the ability to read from the console using the promlib.  But it can print to it at least.

So for those who want to give it a try, here is my MIPS-ELF tool-chain for Win32, that includes the cisco loader!

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