Custom version of GCC for the Vhex kernel which enable shared object file generation
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Yann MAGNIN 5504805f1b fix GCC dependencies 1 week ago
patchs add scripts to build sh-elf-vhex (gcc, binutils) 2 weeks ago
scripts fix GCC dependencies 1 week ago
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README.md Update 'README.md' 1 week ago
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README.md

sh-elf-vhex - modified GCC for the Vhex kernel projet

Context

This project was born following the discovery of a limitation with GCC on the SuperH architecture see on this subject from 2 years ago:

The generation of dynamic libraries is blocked by GCC (the --shared flag is ignored), because the sh3eb-elf target (the one used for cross-compiling on Casio calculators), does not support this functionality.

I am currently building a kernel of a Casio's calculator for a graduation project and I need this functionality. I had discovered, thanks to Lephenixnoir, that we could generate 'shared' libraries by using directly ld with a custom linker script, but this workaround was of short duration. Indeed, we are dependent on a library called libgcc, which provide some useful critical primitives and which is generated only statically (therefore with non-relocatable code), which broke all shared object file generated with this dependencie (and a lot of cases can involve this librarie).

With the help of Lephenixnoir, we tried to add a target for the superH architecture called sh-elf-vhex, allowing us to enable these features and that's what we finally came up with.

This repository gathers only the files that we had to modify for binutils and GCC, as well as scripts to automate the installation of this particular GCC.

Build

The build is relatively simple and can be done in two different ways: you can use the compile.sh script which is at the root of the repository:

./compile /your/installation/path

Or you can use the giteapc tool, created by Lephenixnoir:

giteapc install sh-elf-vhex

It takes about twenty minutes for the build.

Technical notes

The GCC build takes much longer than the sh3eb-elf target because we have two stages for the GCC build. In order, we have:

  • download + configuration of binutils sources
  • download + configuration of GCC sources
  • compilation of binutils
  • compilation of GCC (stage-1) without enabling the shared library functionality
  • compilation of OpenLibM (a dependency of our standard C library)
  • compilation of fxlibc, our custom C standard library
  • compilation of GCC (stage-2) with activation of the shared library fonctionality
  • installation of our C library
  • compilation of the shared libgcc

As for the details of the sh-elf-vhex target that we created:

  • machine-specific features:
    • (t-slibgcc) compilation of the shared libgcc
    • (t-libgcc-pic) the compilation of the libgcc in PIC
    • (t-fdpbit) compilation of the library for emulated floating point numbers
  • global configuration:
    • only C is supported
    • only big endian encoding is supported
    • we use the stdint header from newlib. Otherwise, the generation of stdint.h is incomplete
    • we only target the SH4A-NOFPU processor (no backward compatibility with the SH3 assembler)
    • each public symbol begins with an underscore
    • by default, we link our own C library to each generation of an object file
    • we do not provide a specialized default linker script (for the moment)

Special thanks

A big thanks to Lephenixnoir who helped me a lot for the modification of the sources and made this project possible!