Re: How to get the call stack?

[Sam S. <sd...@gn...>]

[redirected to <clisp-devel>]

> * In message <157...@ho...>
> * On the subject of "Re: [clisp-list] How to get the call stack?"
> * Sent on Thu, 3 Oct 2002 02:56:17 +0200 (CEST)
> * Honorable Bruno Haible <ha...@il...> writes:
>
> Sam writes:
> 
> > What about SP - does it already contain the information necessary to
> > split STACK into funcall sections or not?
> 
> No it doesn't. Functions which don't use UNWIND-PROTECT, CATCH and
> similar special forms don't have SP entries of their own at runtime.

this is very unfortunate.

what about the following approach (a la Emacs):

struct backtrace_t {
  struct backtrace_t* next;
  object* stack; /* will allow debug.d to group STACK around funcalls */
  object caller;
  char nargs;
}

/* kept in the subr_self's register when that is present: */
global struct backtrace_t* backtrace_list;

#define subr_self backtrace_list->caller

replace each

        subr_self = FOO; funcall(FOO,N);

with

        WITH_BACKTRACE(FOO,N,{funcall(FOO,N);});

#define PUSH_BACKTRACE(fun,num,form) \
  do { struct backtrace_t nbt, *obt=backtrace_list; \
    nbt.next = backtrace_list;\
    nbt.stack = &STACK;\
    nbt.caller = fun;\
    nbt.nargs = num;\
    backtrace_list = &nbt;\
    form; \
    backtrace_list = obt;\
  } while(0)

we can make GC treat the contents of backtrace_list specially
(so that 'caller' is updated by it)

a small problem is that when the function is called directly, the
number of arguments is not known (?) -- we can just set nargs to -1

another small problem is that the increase of C stack use.
what performance loss would you expect here?

the biggest problem is longjmp() -- will it restore backtrace_list?
another biggie is unwinding - we will have to make framepointers keep
track of backtrace_list?  Or maybe enter_frame_at_STACK() will unwind
backtrace_list till it points the appropriate STACK segment?

Comments?

-- 
Sam Steingold (http://www.podval.org/~sds) running RedHat7.3 GNU/Linux
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