---
sidebar_label: OS-dev (flat-bin + archive)
---

# Pure ASM / boot image (flat-bin + archive)

Minimal OS-dev style pipeline: assemble raw binaries with NASM, then pack a FAT floppy/image with an optional boot sector.

## Project layout

```
myos/
  dcr.toml
  src/
    boot.asm      # boot sector (512 bytes)
    kernel.asm    # payload
```

For multiple flat artifacts, use a **workspace** (one member per binary) or separate packages; a single `flat-bin` package produces one binary per source stem.

## Boot package (`flat-bin`)

```toml
[package]
name = "boot"
version = "0.1.0"

[build]
language = "asm"
compiler = "nasm"
kind = "flat-bin"
extension = "bin"
roots = ["src/boot.asm"]
```

```bash
dcr build
# → target/<…>/debug/boot.bin  (NASM -f bin, no link)
```

## Disk image after build

```toml
[archive]
output = "target/{profile}/disk.img"
format = "fat12"
size = "1440K"
label = "MYOS"
bootsector = "target/{profile}/boot.bin"

[[archive.layout]]
from = "target/{profile}/kernel.bin"
to = "KERNEL.BIN"
```

* `format`: `fat12`, `fat16`, or `fat32`
* `size`: bytes or `K`/`KB`/`M`/`MB`/`G`/`GB` (default ~1.44 MiB)
* `bootsector`: written only when `offset` is omitted or `0`
* `from` may be a glob; `{profile}` is substituted in paths

## C kernel → flat binary

```toml
[build]
language = "c"
compiler = "clang"
kind = "flat-bin"
freestanding = true
filename = "kernel"
extension = "bin"
ldflags = ["-T", "linker.ld"]
```

Pipeline: objects → temporary linked ELF → `objcopy -O binary` → `kernel.bin`. Requires `objcopy` / `llvm-objcopy` in PATH.

## Other assemblers

| Tool     | Notes                                                                                   |
| -------- | --------------------------------------------------------------------------------------- |
| **FASM** | Write `format binary` in the source; DCR writes `\<stem>.bin` directly |
| **GAS**  | Assemble `.s` → obj → `objcopy -O binary`                                               |
| **LLC**  | `language = "llvm_ir"` → obj → objcopy                                                  |
| **MASM** | COFF obj → objcopy (needs binutils/LLVM objcopy)                                        |

## Notes

* Single-file `roots` are supported: `roots = ["src/boot.asm"]`.
* `--force` re-runs `build.steps` / `build.post_steps` as well as recompilation.
* Prefer `kind = "elf"` if you need a relocatable ELF kernel without stripping to raw binary.