[m-dev.] tests in tests/debugger/declarative failed

[Fergus Henderson]

On 15-Feb-2000, Mark Anthony BROWN <dougl at cs.mu.OZ.AU> wrote:
> Fergus Henderson writes:
> 
> > Also the `aadebug' test case there is failing in grades
> > none.gc and reg.gc; the symptom seems to be a crash
> > at runtime.
> > 
> > Mark, could you please investigate these test case failures?
>
> That problem is caused by some macros in trace/mercury_trace_declarative.h
> which access Mercury data, using fixed numbers for the tag
> and offset.  The fixed numbers are not correct for those grades.
> What is the best way to calculate the correct tag and offset
> in any grade?

[summarizing a discussion we had on this:]

- Actually the tag numbers are currently the same in all grades;
  they differ depending on the number of tag bits available,
  which depends on the architecture (32- or 64-bit).

- The most portable / least implementation-dependent way of accessing
  Mercury data is to write access predicates/functions in Mercury and
  use `pragma export' to export them to C.  
  
  However, in the current implementation this will not be as efficient
  as using the MR_field() etc. macros to access the data structures
  directly.

- If the C code needs to do destructive update on the terms, you can
  still use the technique mentioned above; the Mercury code can use the
  "references" interface in library/store.m (specifically store__init,
  store__new_ref, store__arg_ref, store__set_ref, and
  store__extract_ref_value) to perform the destructive update.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>  |  of excellence is a lethal habit"
PGP: finger fjh at 128.250.37.3        |     -- the last words of T. S. Garp.
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