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From: wpp@marie.physik.TU-Berlin.DE (Kai Petzke)
Newsgroups: comp.lang.beta
Subject: Re: How to immediately compile/load patterns
Date: 6 Mar 96 13:06:33 GMT
Organization: Technical University Berlin, Germany
Lines: 76
Message-ID: <wpp.826117593@marie.physik.TU-Berlin.DE>
References: <4hf6pjINNbul@hood.sps.mot.com>
NNTP-Posting-Host: marie.physik.tu-berlin.de

moss@risc.sps.mot.com (Matthew Moss) writes:

>I am experimenting with an environment where I need to compile a pattern
>located in some text file and immediately be able to access that pattern
>in the running program. Something like this:

Well, as was already pointed out, there is no "straightforward"
solution for this.  However, using "hacker" methods, your plan
should actually do doable.  The following is derived from the
(tested) scheme to dynamically load code into C programs:

step 1:
write your BETA code to a file.

step 2:
call the BETA compiler for that code:
	system("beta -c file.bet");

step 3:
load that object into a dynamic shared object:
	system("ld -r -shared -o file.so file.o");

step 4:
Use the C function "dlopen" to load that shared library:
	void *handle = dlopen("file.so", RTLD_NOW);

step 5:
With `dlsym(void *handle, char *symname)' you can find out, which
symbol of the shared object has been loaded to which address.

It is probably a bad idea to try to directly call a DO part.  But
what might work, is to find the pointer to the pattern data structure
in the loaded object, and transfer that pointer to a pattern variable.

This should be doable without using assembler hacks, but you will
have to study the assembler output of the Mjolner system, so that
you actually know, how it stores pattern variables.  Note, that
each pattern variable holds two fields - a pointer to the pattern
data structure, and a pointer to the enclosing object.


You will want to write a C function, that performs all the steps
mentioned above.  Call that C function from BETA as follows:

	(#
	   p: ##object;
	   DynLoader: external (# a: [1] @char; r: @integer enter (a,r) #);
	do
	   (* Dummy is a pattern, that is defined in the same ATTRIBUTES
	    * section as the pattern, that will be dynamically loaded *)
	   dummy##->p##;
	   ("file.bet", @@p)->DynLoader;
	   (* Now p is ready for use *)
	#);

>My first guess would be to read the COFF information out of the .o file
>produced from the compile. But since I plan on adding the pattern to
>a persistent store, maybe there is an easier way via a temporary PS.
>has anyone done this before? Thanx...

Making these "temporary" patterns compatible with persistent stores
is another tough thing.  In particular, temporary stores need a list
of all possible types, if they load objects from a store.  I don't
know, how this list can be generated in case of dynamically generated
objects ...





Kai
--
Kai Petzke, Technical University of Berlin, Germany
http://www.physik.tu-berlin.de/~wpp/ to learn about Linux, Postgres and BETA.
wpp@marie.physik.tu-berlin.de for regular e-mail
How fast can computers get?  --  Warp 9, of course, on Star Trek.