155 lines
6.8 KiB
Markdown
155 lines
6.8 KiB
Markdown
# MontaukOS Toolchains
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Two cross toolchains live here, both installed to `toolchain/local/`:
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| Script | Triple | Purpose |
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|--------|--------|---------|
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| `build-toolchain.sh` | `x86_64-elf` | Bare-metal compiler for the kernel |
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| `build-montauk-toolchain.sh` | `x86_64-montauk` | OS-aware compiler for userspace programs |
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Both use Binutils 2.43.1 + GCC 14.2.0 and share the source trees in
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`src/`. The Montauk target is added by the patches in `patches/` plus
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the target header `files/montauk.h` (installed as
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`gcc/config/montauk.h` in the GCC tree).
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## The x86_64-montauk target
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`x86_64-montauk-gcc` knows the Montauk userspace ABI, so a hosted
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program builds with no special flags:
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```bash
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toolchain/local/bin/x86_64-montauk-gcc hello.c -o hello.elf
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```
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What the target does by default:
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- Links static, non-PIE `ET_EXEC` binaries (what the kernel ELF loader
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in `kernel/src/Sched/ElfLoader.cpp` accepts), text at 0x400000.
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- `-z max-page-size=0x1000` — the loader maps 4 KiB pages; the x86-64
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default of 2 MiB segment alignment would bloat every binary.
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- Startup/link line: `crt1.o crti.o crtbegin.o ... -lc crtend.o crtn.o`
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taken from the sysroot (`toolchain/sysroot/usr/lib`), which is
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assembled from `programs/lib/libc` by the build script.
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- Headers resolve against the sysroot (`toolchain/sysroot/usr/include`),
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assembled from `programs/include/libc` plus the `montauk/` SDK
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headers. `#include <stdio.h>` just works; no `-nostdinc` needed.
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- `-mno-red-zone` (the project-wide userspace convention). Standard
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hard-float SysV ABI otherwise; pass `-mno-sse` etc. per program if
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wanted.
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- Defines `__montauk__` / `__MONTAUK__`.
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C++ works with `-fno-exceptions -fno-rtti` (the project convention).
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There is no libstdc++ yet — only libgcc is built. A hosted libstdc++
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needs a more complete libc and is the next step toward self-hosting.
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## Refreshing the sysroot
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The sysroot is rebuilt every time `build-montauk-toolchain.sh` runs
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(the compiler build steps are skipped once installed). After changing
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libc headers or the libc itself, re-run the script to refresh it.
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## Layout
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```
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toolchain/
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build-toolchain.sh # bare-metal x86_64-elf (kernel)
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build-montauk-toolchain.sh # x86_64-montauk (userspace)
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patches/ # Montauk target patches (checked in)
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files/montauk.h # GCC target header (checked in)
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src/ # downloaded + patched sources (ignored)
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build/ # build trees (ignored)
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local/ # install prefix (ignored)
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sysroot/ # generated target sysroot (ignored)
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```
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## Native binutils (runs on MontaukOS)
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The whole native SDK (binutils + GCC below, staged for the OS image) is
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built by one idempotent script — this is what a fresh clone should run:
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```bash
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make sdk # from the repo root; wraps toolchain/build-native-sdk.sh
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```
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It invokes build-montauk-toolchain.sh first (cross compiler + sysroot),
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applies the host-build fix-ups listed under "Host-build gotchas", and
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strips the staged binaries. To force a rebuild after libc changes:
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`rm -rf toolchain/native toolchain/native-gcc toolchain/build/binutils-native
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toolchain/build/gcc-native` and re-run. The manual steps below are kept
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as a reference for what the script does.
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Binutils can be cross-compiled to run *on* MontaukOS itself
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(`--host=x86_64-montauk`), the first step toward a self-hosted GCC:
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```bash
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mkdir -p toolchain/build/binutils-native && cd toolchain/build/binutils-native
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export PATH=$PWD/../../local/bin:$PATH
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../../src/binutils-2.43.1/configure \
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--build=x86_64-pc-linux-gnu --host=x86_64-montauk \
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--target=x86_64-montauk --prefix=/sdk \
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--disable-nls --disable-werror --disable-gprofng --disable-gold \
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--disable-plugins --disable-shared --enable-static
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make -j$(nproc) all-gas all-ld all-binutils
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make install-strip-gas install-strip-ld install-strip-binutils \
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DESTDIR=$PWD/../../native
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```
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## Native GCC (runs on MontaukOS)
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GCC itself cross-builds for the montauk host (build dir
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toolchain/build/gcc-native, install DESTDIR toolchain/native-gcc):
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```bash
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../../src/gcc-14.2.0/configure \
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--build=x86_64-pc-linux-gnu --host=x86_64-montauk \
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--target=x86_64-montauk --prefix=/sdk \
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--with-native-system-header-dir=/sdk/include \
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--with-build-sysroot=$PWD/../../sysroot \
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--enable-languages=c,c++ --disable-nls --disable-shared \
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--disable-multilib --disable-gcov --disable-lto --disable-plugin \
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--disable-bootstrap --disable-fixincludes --with-newlib \
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--enable-initfini-array --disable-wchar_t --disable-libstdcxx-pch \
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--with-gnu-as --with-gnu-ld
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ac_cv_c_bigendian=no make -j$(nproc) all-gcc
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make install-gcc DESTDIR=$PWD/../../native-gcc
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```
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Host-build gotchas, in the order they bite:
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- The bundled gmp/mpfr/mpc/isl/gettext carry their own config.sub
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copies; overwrite each with the patched top-level one.
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- Remove the src tree's gettext symlink (--disable-nls does not skip
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it, and its gnulib needs more locale surface than the libc has).
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- gmp.h sniffs the libc's stdio include-guard name to detect FILE;
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the Montauk stdio.h defines the conventional _STDIO_H marker.
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- The gcc subdir configure cannot run host binaries to probe
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endianness; preset ac_cv_c_bigendian=no.
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- The build sysroot needs an sdk -> usr symlink so
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--with-native-system-header-dir=/sdk/include resolves at build time.
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The devkit target ships gcc/g++/cpp as .elf in 0:/sdk/bin, cc1 +
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cc1plus + collect2 (and a copy of ld for collect2's search) under
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0:/sdk/libexec/gcc/x86_64-montauk/14.2.0, libgcc.a + crtbegin/crtend
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under 0:/sdk/lib/gcc/x86_64-montauk/14.2.0, and a 0:/tmp scratch dir
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for driver intermediates.
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Notes:
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- Build only `all-gas all-ld all-binutils`. gprof needs fscanf with
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%[] scansets (not in the Montauk libc); gold and gprofng are
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disabled outright.
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- The libc gained a large POSIX surface for this port (fd functions,
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full errno/signal sets, struct stat, sys/wait.h, utime.h, wchar.h,
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sys/param.h, memory.h, bsearch, sscanf field widths, ...). pex-style
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process spawning (fork/exec/pipe) is stubbed to fail with ENOSYS:
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the tools themselves never spawn, and real process plumbing is the
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posix_spawn milestone that needs kernel support (exit codes in
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SYS_WAITPID, fd redirection wiring).
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- The `devkit` target in programs/GNUmakefile ships the staged tools
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into the OS image at 0:/sdk/bin (as.elf, ld.elf, ar.elf, ...) with a
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target-side sysroot at 0:/sdk/include + 0:/sdk/lib (libc.a, crt
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objects, empty libm/libstdc++) - the Montauk SDK. The kernel
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resolves driveless absolute paths ("/sdk/lib") against the cwd
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drive, so the --prefix=/sdk layout works natively. The shell
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searches 0:/sdk/bin and tab-completes it. Future ports configure
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with --prefix=/sdk. If toolchain/native/ has not been built the
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devkit step is skipped and the image builds without it.
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