RE: Intermixing C-stack with Lua-stack

[Richter, Jörg <Joerg.Richter@...>]

>I'd be curious to hear more if you have luck extracting a co-mingled C/Lua
>stack reliably. I've considered taking a crack at that myself.

My use-case is to get a backtrace from the running process. It would be 
best if there is a solution that works from signal-handlers. But that is 
optional.

So I tried to solve the problem and got some nice results. I've used 
libunwind to find all luaV_execute calls and to query all 
callee-safed registers. The lua_State pointer happened to be in 
RBX (x86_64). From there it was easy to call lua_debug&co.

Of course the register isn't fixed. But for one set of 
optimisation-settings it should always be se same, I think.
And the case that the lua_State pointer isn't saved to the stack 
is also possible. Then you have to modify luaV_execute to force L
to be pushed on the stack somehow.

The next problem is to identify which Lua calls belong to this 
luaV_execute call. This should be easy to solve. Just print the 
Lua function till the first C-function. The next time you hit 
luaV_execute with the same L-pointer print the next Lua-functions 
until the second C-function. And so forth. Might be harder, I haven't 
implemented it yet.

A more portable solution might be to let the luaV_execute function 
register its activation record somewhere and use this information 
instead of the stack peeking.

   Jörg