feat: x86_64-montauk userspace cross toolchain

Add build-montauk-toolchain.sh: builds an OS-aware cross GCC/binutils (same versions and prefix as the bare-metal x86_64-elf toolchain) whose x86_64-montauk target links static ET_EXEC binaries against the Montauk libc sysroot with no special flags: 4 KiB max page size for the kernel ELF loader, -mno-red-zone by default, crt1/crti/crtn + -lc from the sysroot, __montauk__ defined. Target patches are checked into toolchain/patches/, the GCC target header into toolchain/files/. sys/types.h now includes <stdint.h> so hosted code (libgcov and friends) sees intptr_t via the stdio include chain. Co-Authored-By: Claude Fable 5 <[email protected]>
2026-07-14 10:19:35 +02:00
parent 182520a585
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+# MontaukOS Toolchains
+
+Two cross toolchains live here, both installed to `toolchain/local/`:
+
+| Script | Triple | Purpose |
+|--------|--------|---------|
+| `build-toolchain.sh` | `x86_64-elf` | Bare-metal compiler for the kernel |
+| `build-montauk-toolchain.sh` | `x86_64-montauk` | OS-aware compiler for userspace programs |
+
+Both use Binutils 2.43.1 + GCC 14.2.0 and share the source trees in
+`src/`. The Montauk target is added by the patches in `patches/` plus
+the target header `files/montauk.h` (installed as
+`gcc/config/montauk.h` in the GCC tree).
+
+## The x86_64-montauk target
+
+`x86_64-montauk-gcc` knows the Montauk userspace ABI, so a hosted
+program builds with no special flags:
+
+```bash
+toolchain/local/bin/x86_64-montauk-gcc hello.c -o hello.elf
+```
+
+What the target does by default:
+
+- Links static, non-PIE `ET_EXEC` binaries (what the kernel ELF loader
+  in `kernel/src/Sched/ElfLoader.cpp` accepts), text at 0x400000.
+- `-z max-page-size=0x1000` — the loader maps 4 KiB pages; the x86-64
+  default of 2 MiB segment alignment would bloat every binary.
+- Startup/link line: `crt1.o crti.o crtbegin.o ... -lc crtend.o crtn.o`
+  taken from the sysroot (`toolchain/sysroot/usr/lib`), which is
+  assembled from `programs/lib/libc` by the build script.
+- Headers resolve against the sysroot (`toolchain/sysroot/usr/include`),
+  assembled from `programs/include/libc` plus the `montauk/` SDK
+  headers. `#include <stdio.h>` just works; no `-nostdinc` needed.
+- `-mno-red-zone` (the project-wide userspace convention). Standard
+  hard-float SysV ABI otherwise; pass `-mno-sse` etc. per program if
+  wanted.
+- Defines `__montauk__` / `__MONTAUK__`.
+
+C++ works with `-fno-exceptions -fno-rtti` (the project convention).
+There is no libstdc++ yet — only libgcc is built. A hosted libstdc++
+needs a more complete libc and is the next step toward self-hosting.
+
+## Refreshing the sysroot
+
+The sysroot is rebuilt every time `build-montauk-toolchain.sh` runs
+(the compiler build steps are skipped once installed). After changing
+libc headers or the libc itself, re-run the script to refresh it.
+
+## Layout
+
+```
+toolchain/
+  build-toolchain.sh           # bare-metal x86_64-elf (kernel)
+  build-montauk-toolchain.sh   # x86_64-montauk (userspace)
+  patches/                     # Montauk target patches (checked in)
+  files/montauk.h              # GCC target header (checked in)
+  src/                         # downloaded + patched sources (ignored)
+  build/                       # build trees (ignored)
+  local/                       # install prefix (ignored)
+  sysroot/                     # generated target sysroot (ignored)
+```