# How to build a Lua binary with MSYS2 that does not depend on MinGW-w64’s DLLs

As an environment for building Windows binaries [MSYS2](https://msys2.github.io/) improves upon [MinGW](http://mingw.org/)/MSYS in [several important ways](http://stackoverflow.com/a/25023611). When you switch, however, you will notice that its builds of Lua, unlike those produced with plain old `mingw-base`, depend upon external DLLs by default.

![\"Lua.exe - System Error\" screenshot](/media/lua-msys2/lua-dll-missing.png){.center-block}

When you build Lua 5.1.5 with MSYS2's 32-bit version of MinGW-w64 using the command `make mingw` you end up with a `lua51.dll` that requires `libgcc_s_dw2-1.dll` and `libwinpthread-1.dll`:

```sh
$ wget https://www.lua.org/ftp/lua-5.1.5.tar.gz
$ tar xvf lua-5.1.5.tar.gz
$ cd lua-5.1.5/src/
$ make mingw
$ ldd lua51.dll
	ntdll.dll => /c/WINDOWS/system32/ntdll.dll (0x7c900000)
	kernel32.dll => /c/WINDOWS/system32/kernel32.dll (0x7c800000)
	msvcrt.dll => /c/WINDOWS/system32/msvcrt.dll (0x77c10000)
	libgcc_s_dw2-1.dll => /mingw32/bin/libgcc_s_dw2-1.dll (0x6eb40000)
	libwinpthread-1.dll => /mingw32/bin/libwinpthread-1.dll (0x64b40000)
```

If you want fewer DLLs to manage, you have several options. For a quick fix you could build a Lua interpreter statically with `make all`—but then you would not be able to use binary modules, which expect a `lua51.dll`. A solution that keeps `lua51.dll` is explained below.

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The output of `ldd` and the message box in the screenshot mentions `libgcc_s_dw2-1.dll`, which means the library `lua51.dll` depends on a dynamically linked copy of [`libgcc`](https://gcc.gnu.org/onlinedocs/gccint/Libgcc.html). We should be able to use GCC's flag `-static-libgcc` to ensure `libgcc` is linked statically. The makefile for Lua has a section for user-supplied settings with the variables `MYCFLAGS` and `MYLDFLAGS` for the compiler and the linker flags respectively. However, convenience build targets like `mingw` actually ignore those. Let's look at the target `mingw` itself, then, with an eye for what to change there:

```make
mingw:
	$(MAKE) "LUA_A=lua51.dll" "LUA_T=lua.exe" \
	"AR=$(CC) -shared -o" "RANLIB=strip --strip-unneeded" \
	"MYCFLAGS=-DLUA_BUILD_AS_DLL" "MYLIBS=" "MYLDFLAGS=-s" lua.exe
	$(MAKE) "LUAC_T=luac.exe" luac.exe
```

The first command runs `make` recursively to build both `lua51.dll` (`LUA_A`) and `lua.exe` (`LUA_T`) with a predefined set of `MY*` flags.

To keep the original target intact for reference, we'll make a copy of it named `mingw-w64` and modify that. If we put `-static-libgcc` in `MYLDFLAGS` or `MYCFLAGS` in the copy, though, it will not accomplish what we are trying to do. Why? If you search the makefile for the target `LUA_A` you will find the following:

```make
$(LUA_A): $(CORE_O) $(LIB_O)
	$(AR) $@ $(CORE_O) $(LIB_O) # DLL needs all object files
	$(RANLIB) $@
```

It turns out that it is the `$(AR)` command that creates `lua51.dll`. Looking at the target `mingw-w64` we can see that, despite its name, the variable `AR` is set to `$(CC) -shared -o`, i.e., the `$(AR) $@ ...` command runs GCC. So let's add `-static-libgcc` where we set `AR` and try to build again:

```make
mingw-w64:
	$(MAKE) "LUA_A=lua51.dll" "LUA_T=lua.exe" \
	"AR=$(CC) -shared -static-libgcc -o" "RANLIB=strip --strip-unneeded" \
	"MYCFLAGS=-DLUA_BUILD_AS_DLL" "MYLIBS=" "MYLDFLAGS=-s" lua.exe
	$(MAKE) "LUAC_T=luac.exe" luac.exe
```

```sh
$ make clean
$ make mingw-w64
$ ldd lua51.dll
	ntdll.dll => /c/WINDOWS/system32/ntdll.dll (0x7c900000)
	kernel32.dll => /c/WINDOWS/system32/kernel32.dll (0x7c800000)
	msvcrt.dll => /c/WINDOWS/system32/msvcrt.dll (0x77c10000)
```

There. We've built a `lua51.dll` (and a `lua.exe`) that does not expect an external `libgcc`.

If you want to achieve the same effect without editing the makefile you can use an equivalent command:

```sh
$ make clean
$ make "LUA_A=lua51.dll" "LUA_T=lua.exe" "AR=cc -shared -static-libgcc -o" "RANLIB=strip --strip-unneeded" "MYCFLAGS=-DLUA_BUILD_AS_DLL" "MYLIBS=" "MYLDFLAGS=-s" lua.exe
$ make "LUAC_T=luac.exe" luac.exe
```

## Page metadata

URL: <https://dbohdan.com/lua-msys2.md>

Published 2016-08-30, updated 2021-08-21.

Tags:

- how-to
- Lua
- MSYS2
- old blog
- programming
- Windows

Index: [Old blog](/old-blog).