Unable to pass C function from main application to cqueues.thread

[daurnimator]

$ lua -e 'require"cqueues.thread".start(print, "foo", 1):join()'
lua: /usr/share/lua/5.3/cqueues/thread.lua:72: bad argument #15 to 'start' (/usr/lib/lua: cannot read file data: Is a directory)
stack traceback:
    [C]: in upvalue 'start'
    /usr/share/lua/5.3/cqueues/thread.lua:72: in function '_cqueues.thread.start'
    (command line):1: in main chunk
    [C]: in ?

(Linux, glibc)

It appears that dladdr on a static symbol returns some slightly odd things. In this case, dli_fname is lua (I guess from argv[0]?). When passed to dlopen as this non-absolute path, it tries to look for /usr/lib/lua, which of course doesn't exist.

FWIW I checked what dladdr1 returned in extra_info, and lname was an empty string (not NULL as I would have understood, but an empty string).

[daurnimator]

Hacky workaround for linux that assumes a standard linker script was used:

diff --git a/src/thread.c b/src/thread.c
index 63011b4..d72ba32 100644
--- a/src/thread.c
+++ b/src/thread.c
@@ -238,6 +238,9 @@ static int ct_addfunc(struct cthread *ct, lua_CFunction f) {
    if (!dladdr(EXTENSION (void *)f, &key.info))
        goto dlerr;

+   if (key.info.dli_fbase == (void*)0x400000)
+       return 0;
+
    if ((ent = LLRB_FIND(libs, &ct->libs, &key)))
        return 0;

[daurnimator]

A more portable workaround might be to only allow paths containing a /.