Re: Non-aligned pointer errors on Mac OS X

[Scott Weeks <scott@...>]

Hi again,

I can reproduce the error with this code:

in my c file:

static int pf_debug1(lua_State *L) {
  lua_newtable(L);
  return 1;
}


in my unit test:

function tc:test_t1()
  libpathfind.pf_debug1()
end

Always causes the non-aligned pointer error. When I remove the  
lua_newtable(L) call the error goes away. Can anyone give me some  
insight into how Lua allocates tables and what might be causing this?

When I run the program in gdb the stack always shows that the free  
calls are coming from a garbage collection cycle (which I guess makes  
sense).

I'm running 10.5 (although the problem has occurred on 10.4 as well.)  
On a MacBook Pro Intel Core Duo.

Any help at all would be appreciated since it really doesn't look like  
it's in my code.


On 16/01/2008, at 5:28 PM, Rob Barris wrote:

> On OS X all calls to malloc() will return something aligned in 16  
> byte boundary unless its size is less than 16 bytes or maybe 8 bytes.
>
> So, the runtime is trying to let us know that some code path is  
> possibly freeing a bogus pointer. Frame #4 in your crawl shows the  
> point in Lua code where the call to free() is made.. I wonder if you  
> have found a bug.
>
>
> On Jan 15, 2008, at 5:35 PM, Scott Weeks wrote:
>
> > Hello,
> >
> > I'm new here :-)
> >
> > Anyway, I've been doing some development with Lua and OS X and have  
> > noticed that when I use some C libraries I get the following error  
> > (or something like it)
> >
> > lua(8680) malloc: *** error for object 0x40fa4: Non-aligned pointer  
> > being freed
> > *** set a breakpoint in malloc_error_break to debug
> >
> > This has occured for me with the luasqlite3 library as well as with  
> > a C module that I've been writing. It occurs for me when I create a  
> > new table from within C.
> >
> > Adding a lua_newtable(L) call or a luaL_newmetatable(L,"blah") call  
> > will get me these errors and they stop when I comment them out.
> >
> > Now, I am very much a novice when it comes to C and memory  
> > management and am particularly baffled with things like pointer  
> > alignement, etc... I fired up gdb and managed to get the following  
> > stack when I ran my program with malloc_error_break set
> >
> > Breakpoint 1, 0x94e9b9f1 in malloc_error_break ()
> > (gdb) where
> > #0  0x94e9b9f1 in malloc_error_break ()
> > #1  0x94e969df in szone_error ()
> > #2  0x94dbbb83 in szone_free ()
> > #3  0x94dbb9ed in free ()
> > #4  0x00015c94 in l_alloc ()
> > #5  0x0000c4fc in luaM_realloc_ ()
> > #6  0x00010a3b in luaH_free ()
> > #7  0x0000a71d in sweeplist ()
> > #8  0x0000ab4f in singlestep ()
> > #9  0x0000ae68 in luaC_step ()
> > #10 0x000140ea in luaV_execute ()
> > #11 0x00008e30 in luaD_call ()
> > #12 0x00004951 in f_call ()
> > #13 0x0000833b in luaD_rawrunprotected ()
> > #14 0x00009152 in luaD_pcall ()
> > #15 0x000049c5 in lua_pcall ()
> > #16 0x00016ffa in luaB_xpcall ()
> > #17 0x000089f3 in luaD_precall ()
> > #18 0x00013e9e in luaV_execute ()
> > #19 0x00008e30 in luaD_call ()
> > #20 0x00004951 in f_call ()
> > #21 0x0000833b in luaD_rawrunprotected ()
> > #22 0x00009152 in luaD_pcall ()
> > #23 0x000049c5 in lua_pcall ()
> > #24 0x00002833 in docall ()
> > #25 0x00003024 in pmain ()
> > #26 0x000089f3 in luaD_precall ()
> > #27 0x00008dd3 in luaD_call ()
> > #28 0x00004a90 in f_Ccall ()
> > #29 0x0000833b in luaD_rawrunprotected ()
> > #30 0x00009152 in luaD_pcall ()
> > #31 0x00004ae7 in lua_cpcall ()
> > #32 0x00003405 in main ()
> >
> >
> > I don't know if that's useful but it seems to be right around the  
> > palce where lua is reallocating memory... Any pointers would be  
> > greatly appreciated.
> >
> > Cheers,
> > Scotty Weeks