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diff --git a/Fosdem2024/contents.md b/Fosdem2024/contents.md new file mode 100644 index 0000000..4c8b74e --- /dev/null +++ b/Fosdem2024/contents.md @@ -0,0 +1,271 @@ +--- +title: RISC-V Bootstrapping in Guix and Live-Bootstrap +subtitle: Status report for 2023, and what's coming up next + +license: CC-BY-SA +author: Ekaitz Zárraga +links-as-notes: true +lang: spanish +polyglossia-lang: + name: english +how-to: pandoc -f markdown+smart -t beamer contents.md -o beamer.pdf --pdf-engine=xelatex --template=template.tex +convert-img: inkscape IN.svg --export-filename OUT.png --export-type=png --export-background-opacity=0.0 # NOT NEEDED! +header-includes: + - \usepackage{multicol} + - \newcommand{\hideFromPandoc}[1]{#1} + - \hideFromPandoc{ + \let\Begin\begin + \let\End\end + } +... + +## Before we start + +If you want details and don't mind reading large text walls full of +nitty-gritty details, you can leave this talk and read [all the blogposts I did +on the process](https://ekaitz.elenq.tech/tag/bootstrapping-gcc-in-risc-v.html) + +**You can still stay here and smile, too.** + +## Who I am + +- Telecommunication engineer (EEE equivalent) +- Freelance engineer/programmer at [ElenQ.Tech](https://elenq.tech) +- Guix user and contributor +- You might remember me from my talk last year: + *"Bringing RISC-V to Guix's bootstrap"* + + + +## Context + +- In 2021 [NlNet][nlnet-grant-i] funded me to do some bootstrapping work: I + backported RISC-V support to GCC 4.6.4 from 7.5, and to our TinyCC-Boot from + upstream TinyCC. These were fundamental points in our bootstrap chain. +- I explained that in [FOSDEM 2023][fosdem-2023]. + +[nlnet-grant-i]: https://nlnet.nl/project/GNUMes-RISCV/index.html +[fosdem-2023]: https://archive.fosdem.org/2023/schedule/event/guixriscv/ + +\hfill {height=25px}\ +\hfill {height=15px} + + +## Intro + +- The work wasn't finished so I asked for a [second grant to + NlNet][nlnet-grant-ii]. +- I was tired of the previous effort and I needed help. I decided to bring more + people to the project: + - **Andrius Štikonas**: Involved in `live-bootstrap`, `stage-0` and the + related projects. Has the context awareness I lack. + - **Janneke**: `Mes` maintainer and author, `TinyCC-boot` maintainer and + `guix` contributor. All these projects are structural to the + bootstrapping process. + - More people +- My goal was to pay people for their good work, using the success of my + previous effort as a lever to get funded. + +[nlnet-grant-ii]: https://nlnet.nl/project/GNUMes-RISCV-bootstrap/ + +\hfill {height=25px}\ +\hfill {height=15px} + + +# In pictures + +## Bootstrapping process - Before + +\Begin{multicols}{2} + +- Colors represent RISC-V support: + - **\textcolor{red}{RED}**: no RISC-V support + - **\textcolor{orange}{ORANGE}**: some RISC-V support + - **\textcolor{green}{GREEN}**: full RISC-V support +- **TinyCC-boot** and **GCC (old)** are **\textcolor{red}{RED}**. +\vfill + +\columnbreak + + + +\End{multicols} + +## Bootstrapping process - After the Backport (2022) + +\Begin{multicols}{2} + +- **Arrows** are still **\textcolor{red}{RED}** +- At that time I didn't know **TinyCC** was **\textcolor{orange}{ORANGE}**, + that was discovered later +- **GCC (old)** was actually **\textcolor{green}{GREEN}ER** than I thought +\vfill + +\columnbreak + + + +\End{multicols} + +## Bootstrapping process - Now + +\Begin{multicols}{2} +- **TinyCC-Boot** is **\textcolor{green}{GREEN}** now +- The **\textcolor{green}{GREEN}** rectangle is included in `Guix` and + `live-bootstrap` +- **GCC (old)** is **\textcolor{green}{GREEN}** now: Tested in Debian in real + RISC-V hardware. +\vfill + +\columnbreak + + + +\End{multicols} + +## Bootstrapping process - Future + +\Begin{multicols}{2} +- **\textcolor{red}{->} TinyCC** requires changes in MesLibC +- **\textcolor{red}{->} GCC (old)**: + - requires `make` + - TinyCC claims to be able to build GCC 4, but we didn't test that (i386 + bootstrap uses GCC 2.95 in between). +- **\textcolor{red}{->} GCC** should *just work* +- A powerful `libc` is needed, built with TinyCC, which doesn't support + Extended Assembly. +\vfill + +\columnbreak + + + +\End{multicols} + + +# Questions? + +## + +<!-- EXTRA --> + +# Limitations of the backport + +## TinyCC + +- I only tested the backend, in an emulated environment, using a using TinyCC + as a cross-compiler +- I tested on **GLibC**, but in the bootstrapping process it uses **MesLibC**, + a minimal **LibC**, part of Mes. +- **TinyCC-Boot** is in fact compiled several times (up to 6) with different + features (using conditional compilation via macro definitions like `-D...`). + - In a cross compiled environment this is not possible to test +- I didn't test the TinyCC **RISC-V assembler**, which happened to be + unimplemented (yeah... LOL), and it's needed for the **LibC**. + +## TinyCC + + + +## GCC + +- I tested it as a Cross-Compiler, so only the backend was tested. Again, no + bootstrap[^gcc-bootstrap]. +- It never compiled itself +- I didn't work on the C++ support + +[^gcc-bootstrap]: GCC has a bootstrap process that checks if the compiler works + correctly. First, it's compiled with your compiler of choice. Then, the + resulting binary is used to compile the GCC codebase again. The result of + that compiles GCC again. Then the binaries are compared, to make sure they + are identical. This can't be done in a cross-compiled environment, for + obvious reasons. + +# The work + +## TinyCC-Boot + +We focused on this, and let the other projects be carried by this effort. + +- Andrius and I spent many nights debugging crazy things in here. +- TinyCC's codebase is hard to read +- Many errors we got were not reproducible using a TinyCC compiled with GCC, so + we needed to build it from MesCC, which is very slow +- MesCC doesn't provide very helpful debug symbols +- We learned many things as we went + +> I wouldn't have the energy to make this without Andrius. + +## TinyCC-Boot - Crazy things + +1. Body is never executed: + + ``` c + if ( x < 8 ) { + // body + } + ``` +2. `A << 20 >> 20` +3. `__global_pointer$ is not a valid symbol` +4. Assembler uses a weird syntax and doesn't support Extended Assembly +5. `cannot cast from/to void` +6. And segfaults, segfaults everywhere! + +[Read more about them here](https://ekaitz.elenq.tech/bootstrapGcc8.html) + +## TinyCC-Boot - Results + +We finally managed to bootstrap TinyCC-Boot. + +- Andrius included the [build recipe in `live-bootstrap`](https://github.com/fosslinux/live-bootstrap/blob/master/steps/tcc-0.9.26/pass1.kaem) +- I did the [`guix` recipe](https://issues.guix.gnu.org/68222) + +## GNU Mes + +The problems we found in **TinyCC-Boot** made us improve Mes in several ways: + +- **MesCC**, the C compiler, had some limitations that were unnoticed in the i386 + bootstrap that appeared in RISC-V: faulty `switch-case`s, wrong `struct` + initializations, some integer weirdness... +- **MesLibC**, had to be split for our TinyCC as it doesn't support Extended + Assembly, and it also needed some extra tweaks: `char` signedness, `va_args` + support, build script support for the changes... + +> Having Janneke with us made the process very smooth. + + +## GCC + +- We compiled GCC with itself in a Debian machine in real RISC-V hardware +- Including C++ support +- [Only needed a few commits!](https://github.com/ekaitz-zarraga/gcc/compare/working-compiler...riscv) +- Guix recipe is pending, as we need to fix other steps to be able to add this: + `make`, a proper `libc`, TinyCC... + + +# Last words + +## Last words + +- People is important: I felt alone, and I didn't know how to continue. If I + had to spend another year working alone I would've just rejected the project. + **Bringing people gave me energy, knowledge and emotional support** + +- Money is important: thanks to NlNet I had the chance to pay people for their + work and buy some hardware. Covering people's basic needs is fundamental. + **Getting paid makes people independent, so they can focus on what they are + good at instead of struggling to survive** + +## So + +- Thanks, Andrius and Janneke +- Thanks, NlNet +- And... + +# Thank you + +## Contact and take part + +- Email me: <ekaitz@elenq.tech> +- Relevant IRC channels: `#bootstrappable`, `#guix`, `#guix-risc-v` + |