Windows C Build Toolchain (MSYS2 MinGW GCC)

When to Use

Building C/C++ projects on Windows when Visual Studio Build Tools are not installed or unavailable.

Setup

# Install MSYS2 via winget
winget install MSYS2.MSYS2

# Fix PGP keyring (run once from MSYS2 bash)
C:/msys64/usr/bin/bash.exe -lc "
rm -rf /etc/pacman.d/gnupg
pacman-key --init
pacman-key --populate msys2
"

# Install GCC
C:/msys64/usr/bin/bash.exe -lc "pacman -S --noconfirm mingw-w64-x86_64-gcc"

Build

Always invoke gcc through MSYS2 bash, not directly from Git Bash. Windows Defender silently kills cc1.exe when invoked from Git Bash (the terminal tool). The MSYS2 shell does not have this issue.

# WRONG — fails silently (exit 1, no output):
C:/msys64/mingw64/bin/gcc.exe -c file.c

# CORRECT — works:
C:/msys64/usr/bin/bash.exe -lc "
export PATH=/mingw64/bin:\$PATH
cd /c/Users/admin/projects/myproject
gcc -shared -o library.dll source.c -lkernel32 -ladvapi32
"

Common Fixes

Implicit declaration of function

GCC requires forward declarations. If a function is used in one .c file but defined in another, add extern declaration in a shared header:

// In shared_header.h
extern double my_function(HANDLE handle);

Linking Windows APIs

gcc -shared -o library.dll source.c \
  -lkernel32 -ladvapi32 -lshell32 -lole32 -loleaut32 -lwbemuuid

Pitfalls

• Windows Defender kills cc1.exe from Git Bash: The MSYS2 gcc toolchain works fine from MSYS2 bash but fails silently from Git Bash. Always wrap gcc calls in C:/msys64/usr/bin/bash.exe -lc "...".
• MSYS2 PGP keyring corruption: Fresh MSYS2 install may have invalid package signatures. Fix by removing and reinitializing the keyring.
• Exit code 1 with no output: If gcc exits 1 with no error messages, it is likely being killed by antivirus. Check Windows Defender protection history.
• Missing forward declarations: GCC is stricter than MSVC about implicit function declarations. Every function used in a translation unit must be declared before use.

Reference

See references/w64devkit-lightweight-mingw.md for the alternative lightweight MinGW distribution (~60MB, no installer).