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Building and Running Userspace Programs on ValcOS

Prerequisites

You need a cross-compiler for i686 (32-bit x86):

Option 1: Install pre-built toolchain

# On Windows with MSYS2/MinGW:
pacman -S mingw-w64-i686-gcc

# On Linux:
sudo apt-get install gcc-multilib

Option 2: Build your own cross-compiler

Follow: https://wiki.osdev.org/GCC_Cross-Compiler

Building the Test Program

Step 1: Compile hello.c

i686-elf-gcc -m32 -ffreestanding -nostdlib -fno-pie -fno-stack-protector -c userspace/hello.c -o build/hello.o

Step 2: Link

i686-elf-ld -m elf_i386 -T userspace/linker.ld build/hello.o -o build/hello.elf

Step 3: Verify it's a valid ELF

file build/hello.elf
# Should show: ELF 32-bit LSB executable, Intel 80386

Adding to ValcOS Filesystem

Step 1: Copy to rootfs

cp build/hello.elf rootfs/hello.elf

Step 2: Rebuild disk image

make run

Step 3: Run in ValcOS

ValcOS> ls
ValcOS> exec /hello.elf

Current Limitations

The ELF loader is partially implemented:

  • ✅ Can parse ELF headers
  • ✅ Can identify loadable segments
  • ❌ Cannot allocate user memory yet (needs VMM integration)
  • ❌ Cannot switch to user mode yet (needs ring 3 setup)
  • ❌ Cannot handle syscalls yet

Next Steps

To fully run programs, you need to implement:

  1. User mode switching (ring 0 → ring 3)
  2. VMM integration for user memory allocation
  3. System calls for program interaction
  4. User stack setup

This is Phase 10 completion + Phase 11 (syscalls).

Expected Timeline

  • Phase 10 completion: 1-2 weeks
  • Phase 11 (syscalls): 1 week
  • Phase 12 (newlib): 1-2 weeks

After that, you can run real programs with printf, malloc, etc.!