A different way to bootstrap and build GCC

[Stefan]

Hi!

I got a step further with the different way to build GCC.  The problem not 
using the proper multilib variant for embedded systems is solved now and I 
updated to GCC 14.2.

To cite myself, my gut feeling is that the whole GCC version chain starting in 
(gnu packages commencement) should be build this way.  So I started to play 
around with the bootstrapping of GCC.

Starting with only few packages from (gnu packages commencement) I so far 
managed to build a static GCC 10.4.0 using a static musl 1.2.5.

The initial packages I reuse are:

%bootstrap-guile
gash-boot
bootar
gash-utils-boot
tcc-boot0
gnu-make-mesboot0
gmp-boot
mpfr-boot
mpc-boot


Using only these I build a recent TCC from 2024-08-20 with Mes from tcc-boot0 
as C library, and then MUSL 1.2.5. Then (only) three iterations of TCC with 
musl are needed to get a stable TCC with working floating point support.

The chain continues with GNU Make 4.4.1, Binutils 2.42, Findutils 4.10.0, GCC 
4.6.4 with gmp-boot, mpfr-boot, mpc-boot (the version with the RISC-V patches 
may just work), M4 1.4.19, GMP 6.3.0, MPFR 4.2.1, MPC 1.3.1, GCC 10.4.0.

These are all static builds so far.  I'm using latest versions of all packages, 
except Binutils, whose version 2.43 does not link the object files from TCC.  I 
avoid to use --build=i686-unknown-linux-gnu to make it possible to build for 
other architectures as well.

I think the next step should be GCC 14, then glibc with shared library support 
and GCC 14 again.

I need several small patches to work around shortcomings in Mes, gash, 
gash-utils, missing functionality of version 3.8.0 of gnu-make-mesboot0 
(version 3.81 would have it), bugs in TCC.  They are all described in the 
comments.  Maybe gash and gash-utils could be improved in future.  The most 
annoying thing is that only one core can be used for the builds, otherwise they 
hang.  I guess it is related to gash in combination with %bootstrap-guile, at 
least using Make 4.4.1 makes no difference.

I published a git repository at 
<https://git.pub.solar/stefan/embedded-channel>.  Unfortunately it's not a 
proper channel yet.  If someone likes to give that bootstrap path a try, use this 
command:

guix build --cores=1 -L <your-checkout-here> GCC-10-bootstrap

The working GCCs can be build with

guix build -L <your-checkout-here> GCC GCC-cross-picolibc-arm-none-eabi, 
GCC-cross-newlib-arm-none-eabi

There are GCC…-toolchain package as well, which propagate ld and all the other 
tools from Binutils.  But if these tools are only used indirectly through the 
gcc or g++ drivers, these GCC…-toolchain packages are not needed at all, as the 
GCC packages are standalone.  There are also GCC…-c-toolchain variables for use 
with package-with-c-toolchain.  There is no separate libstdc++ package yet, the 
library is just part of GCC.  A separate package will only be needed for Clang 
or other compilers (maybe Zig), but I'm not sure yet, if clang actually needs a 
dependency to GCC.

I hope this will be useful, maybe it can help the RISC-V bootstrap effort.  I'm 
open for suggestions how to proceed from here.


Bye

Stefan