Lua C API Memory Leak? (valgrind)

Question

I'm trying to write a C program with Lua embedded inside.. And, I tried a very simple program to start, it just creates the Lua context, and then destroys it:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
extern "C" {
    #include <lua.h>
    #include <lauxlib.h>
    #include <lualib.h>
}

int main(int argc, char *argv[]) {
    lua_State *L = lua_open();
    luaL_openlibs(L);

    lua_close(L);
    fprintf(stderr, "%s: %d\n", __FILE__, __LINE__);
    return(0);
}

I'm compiling it like so: (I'm actually using Torch7, so..)

g++ -c -g3 -O2 -Wall -Werror -I/usr/local/torch/install/include/ -fPIC pure_lua_test.C -o pure_lua_test.o
g++ -g3 -O2 -Wall -Werror -I/usr/local/torch/install/include/ -fPIC -o pure_lua_test pure_lua_test.o -L/usr/local/torch/install/lib/ -lluajit

When I run it on it's own, it prints

pure_lua_test.C: 16

as expected, (just before the return).

But, when I run it with valgrind, (as valgrind ./pure_lua_test )

I get

==9165== Memcheck, a memory error detector
==9165== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==9165== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info
==9165== Command: ./pure_lua_test
==9165== 
==9165== Invalid read of size 4
==9165==    at 0x4E9EE97: lua_pushcclosure (in /usr/local/src/torch-2015-05-25/install/lib/libluajit.so)
==9165==    by 0x4EB4CDD: luaL_openlibs (in /usr/local/src/torch-2015-05-25/install/lib/libluajit.so)
==9165==    by 0x400700: main (pure_lua_test.C:13)
==9165==  Address 0x8 is not stack'd, malloc'd or (recently) free'd
==9165== 
==9165== 
==9165== Process terminating with default action of signal 11 (SIGSEGV)
==9165==  Access not within mapped region at address 0x8
==9165==    at 0x4E9EE97: lua_pushcclosure (in /usr/local/src/torch-2015-05-25/install/lib/libluajit.so)
==9165==    by 0x4EB4CDD: luaL_openlibs (in /usr/local/src/torch-2015-05-25/install/lib/libluajit.so)
==9165==    by 0x400700: main (pure_lua_test.C:13)
==9165==  If you believe this happened as a result of a stack
==9165==  overflow in your program's main thread (unlikely but
==9165==  possible), you can try to increase the size of the
==9165==  main thread stack using the --main-stacksize= flag.
==9165==  The main thread stack size used in this run was 8388608.
==9165== 
==9165== HEAP SUMMARY:
==9165==     in use at exit: 0 bytes in 0 blocks
==9165==   total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==9165== 
==9165== All heap blocks were freed -- no leaks are possible
==9165== 
==9165== For counts of detected and suppressed errors, rerun with: -v
==9165== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)

Does anyone know what's happening? Why is it SIGSEGV'ing in valgrind? Is this something I should worry about? Basically, I was hoping to verify that a plugin I was writing for Torch had no memory leaks... But, if it fails with this, then, I'm kind of stuck.

Answer 1

The reason for this issue seems to be Valgrind, not LuaJIT. Valgrind is blocking MAP_32BIT which breaks LuaJIT. To demonstrate, add a check for NULL on lua_State * L and you'll see it is NULL while run under Valgrind, and non-NULL while running regularly.

Here is the modifications I did to your sample:

if(L == NULL) {
    printf("Could not create luaL_newstate()\n");
} else {
    luaL_openlibs(L);
    lua_close(L);
    printf("I can create luaL_newstate fine!\n");
}

When I run this normally:

$ ./pure_lua_test 
I can create luaL_newstate fine!

But when I run it under Valgrind:

$ valgrind ./pure_lua_test
==8211== Memcheck, a memory error detector
==8211== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==8211== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==8211== Command: ./pure_lua_test
==8211== 
Could not create luaL_newstate()
==8211== 

GDB also report that the application exited as it should:

(gdb) run
Starting program: /tmp/pure_lua_test 
I can create luaL_newstate fine!
[Inferior 1 (process 8621) exited normally]

Here is a complete MCVE:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
extern "C" {
        #include <lua.h>
        #include <lauxlib.h>
        #include <lualib.h>
}

int main(int argc, char *argv[]) {
    lua_State *L;
    L = luaL_newstate();

    if(L == NULL) {
        printf("Could not create luaL_newstate()\n");
    } else {
        luaL_openlibs(L);

        lua_close(L);
        printf("I can create luaL_newstate fine!\n");
    }

    return(0);
}

Here is a nice article on MAP_32BIT. Hope this helps in any way.