Re: [eclipse-clp-users] Question about recursion frames in ECLiPSe-CLP

Schüpbach Adrian Laurent wrote:
> Dear ECLiPSe-team
> 
> I'm trying to port ECLiPSe-CLP to a new OS we are currently writing and I'd
> have some questions.
> 
> I started with the minimal set of files needed to build Kernel/<arch>/sepia
> and wanted to get that working first. That means I take the files
> in Kernel/ and Shm/ and I build libeclipse, libshm and libdummies and
> finally link it together with a simple example (eg_c_basic).
> 
> I'm using version 6.0.42.
> 
> I can compile and link the example file which does
> ec_init(), ec_post_string(), ec_resume(), ec_queue_read() and
> ec_cleanup().
> 
> When I try to run it, ec_init() almost terminates, but not completely.
> It reads in lib/kernel.eco and parses it, that seems ok.
> 
> At some point, just before ec_init() terminates, ec_emulate() returns with
> PTHROW due to a recursion frame. PTHROW is returned by
> emu.c at around line 6600 where it checks for the recursion frame.
> 
> 
> I have some questions about that:
> 
> 1. What is a recursion frame and why does it usually get pushed?
> 2. Why would the recursion frame not be expected at this point?
> 3. Which emulator is exited here? Are there several emulators?
> 4. Is there anything I can look for to identify the problem?
> 5. Is there any detailed code documentation?
> 
> 
> This is the piece of code in emu.c at about line 6600 which causes the emulator
> to return PTHROW. IsRecursionFrame(BTop(pw1)) is true while
> IsInterruptFrame(BTop(pw1)) is false.
> 
> 
>         else if (IsInterruptFrame(BTop(pw1))||IsRecursionFrame(BTop(pw1)))
> 		{
> 		// exit an emulator: restore everything from the invoc frame.
>         // Normally we will continue throwing in an earlier emulator
>         // invocation, but that's not sure because the C code can
>         // choose not to propagate the throw. Therefore we must
>         // restore the engine to a reasonable state now rather
>         // than wait for the catch!
>         //
>             err_code = PTHROW;
> 		    B.args = pw1;
> 		    goto _exit_emulator_;	/// (err_code,scratch_pw)
> 		}
>         else	/* other frame, skip it */
> 
> 
> Unfortunately I don't fully understand the code and the execution flow there.
> I hope you can give me some hints what I should look for or how I could
> try to debug.
> 
> Thank you in advance!
> 
> Cheers
> Adrian
> 
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Hi Adrian,

You mentioned in your previous e-mails to me about this that you cross 
compiled ECLiPSe for this OS. For cross-compile to work correctly, you
should have also ran configure for the platform you are cross-compiling 
to. Otherwise, it is possible that some of the platform dependent 
settings may lead to runtime errors with ECLiPSe -- this could be a 
reason you are getting your error.

As to your detailed question about the PTHORW, I am probably not the 
best person to answer questions on it. However, my guess is that there 
was some (unexpected) error in executing the initialisation ECLiPSe code 
when ec_init() is executed, and this is resulting in an error that the 
system is unable to handle.

Cheers,

Kish


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