Compiling Lua with dynamic library support

[Stefano Cossu]

Hello,

I am debugging a segfault in a C extension for Lua and I need to print
out the stack trace to find which Lua line caused the segfault.

In order to see meaningful info in the stack, I compiled Lua from source
activating debug symbols (Lua 5.4.8 on Linux x64):

make linux CFLAGS=-ggdb
sudo make install INSTALL_TOP=/opt/lua-5.4-dbg
sudo ln -s /opt/lua-5.4-dbg/bin/lua /usr/local/bin/lua-dbg

But when I try to import a C module from the debug version, I get an error:

lua-dbg -e 'require "lfs"'
lua-dbg: error loading module 'lfs' from file
'/home/ste/.luarocks/lib/lua/5.4/lfs.so':
dynamic libraries not enabled; check your Lua installation
stack traceback:
[C]: in ?
[C]: in function 'require'
(command line):1: in main chunk
[C]: in ?

Which compile option(s) am I misssing?

Thanks
s

[Gé Weijers]

Hi,

I suspect that overriding CFLAGS on the command line is not a good idea, it overrides the -DLUA_USE_LINUX compiler option, which implies the use of libdl, the dynamic linker interface. I would edit the Makefile in the 'src' directory, and replace -O2 with your -ggdb option temporarily.

Hope this helps.

Gé

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Gé

[Scott Morgan]

On 20/11/2025 17:01, 'Stefano Cossu' via lua-l wrote:
> Hello,
>
> I am debugging a segfault in a C extension for Lua and I need to print
> out the stack trace to find which Lua line caused the segfault.
>
> In order to see meaningful info in the stack, I compiled Lua from source
> activating debug symbols (Lua 5.4.8 on Linux x64):
>
> make linux CFLAGS=-ggdb

Shouldn't that be:

MYCFLAGS=-ggdb make linux

The Lua Makefile (the main one in src/) uses the $(MYCFLAGS) env var to
add options to the build, and the var needs to be set before the make
command rather than after it.

Scott

[Luiz Henrique de Figueiredo]

> Shouldn't that be:
> MYCFLAGS=-ggdb make linux

make linux MYCFLAGS=-ggdb should work just fine both in top-level Lua
dir and in src/

[Stefano]

MYCFLAGS=-ggdb make linux

does not add the flag but 

make linux MYCFLAGS=-ggdb

does while leaving -DLUA_USE_LINUX in place.

Thanks!

s