Re: LuaJIT + glXGetProcAddress

[Henk Boom <henk@...>]

On 2012-03-15, Mike Pall <mikelu-1203@mike.de> wrote:
> Henk Boom wrote:
>> I'm using LuaJIT 2.0.0-beta9 that I've checked out from git. My system
>> is Linux/x64 as well with a cpu that ubuntu lists as "Intel® Atom™ CPU
>> 330 @ 1.60GHz × 4"
>
> Well, I've got a Core2 E8400. But at this point CPU differences
> shouldn't matter at all: the JIT compiler isn't invoked and the
> interpreter is CPU-model-agnostic.
>
> And I've tested with both the released beta9 and git HEAD. Same
> (positive) result here.
>
>> I'm not sure what to try at this point. I know that I have support for
>> glCreateShader, since I've used it before in C/glut/glew programs. Is
>> there some other information I could capture that might make it easier
>> to debug the problem?
>
> Try to recompile everything with debugging turned on and then set
> a breakpoint at glCreateShader. You may have to wait for the
> library to load and/or use the internal symbol name. Check the
> argument it receives (in $rdi). Then set a breakpoint in the
> calling frame and check the result it returns (in $rax).

Okay, so after trying to set a breakpoint I've figured out that the
ffi code is not actually calling glCreateShader. Printing the function
address returned from glXGetProcAddress from lua and from the
native-bound gl__glCreateShader tells me they have different
addresses. In particular, when I purposefully give glXGetProcAddress
an invalid name, it returns null in C, but from the ffi I always get
an address back.

I added these lines to gl__glCreateShader:

  printf("glXGetProcAddress: %p\n", glXGetProcAddress);
  printf("glXGetProcAddressARB: %p\n", glXGetProcAddressARB);
  printf("glCreateShader: %p\n", glCreateShader);

and these to init.lua

  print('glXGetProcAddress', libgl.glXGetProcAddress)
  print('glCreateShader', libgl.glXGetProcAddress('glCreateShader'))

The output I get is a bit different every time, but here's an example:

--------

glfwInit	1
glfwOpenWindow	1
glfw version	2	6	0
opengl version 0.0

this doesn't work
glXGetProcAddress	cdata<void (*())()>: 0x7f4a6c406d50
glCreateShader	cdata<void (*)()>: 0x7f4a6c1d6820
glCreateShader	0

this does
glXGetProcAddress: 0x7f4a6fe09330
glXGetProcAddressARB: 0x7f4a6fe09440
glCreateShader: 0x7f4a70088060
glCreateShader	1
--------

I'm not sure how those numbers make sense. Maybe I just don't
understand how these symbols are resolved at load/run-time, but I
would expect the lua-printed address of glXGetProcAddress to match
with the c-printed one.

    henk