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RE: [22.1.90]: Point before start of properties

From: Marshall, Simon
Subject: RE: [22.1.90]: Point before start of properties
Date: Tue, 19 Feb 2008 10:37:39 -0000

> > Yes.  Btw, I didn't mention before that gcc gives me lots of
warnings of
> > the form "dispnew.c:3061: warning: incompatible implicit declaration
> > built-in function 'alloca'".  (That is the reason why I tried
> > GNU_MALLOC and HAVE_ALLOCA, though IIRC I could not get rid of the
> > warnings and made no difference to the problem of calling error at
> > intervals.c:794.)  Could this be relevant?
> Any warning outside of intervals.c seem unlikely to be a good source
> the problem.  Do you ever get any kind of warning when compiling
> intervals.c?


> Also you said that the problem could be triggered with gcc-4.1.2 even
> without optimization, is that really true?  If so, can you try again
> with gcc-4.1.2 and no optimizations, to get better debug info?

Ah, I did say that didn't I.  A typo I think.  (I cannot reproduce it
without optimisation, though I have since installed 4.2.3 over the top
of 4.1.2.  I tried to reproduce it today with
CC=sparc-sun-solaris2.8-gcc-4.1.2, and I could with CFLAGS="-g -O" and
"-g -O2", but not with CFLAGS="-g".  Apologies for that.)

> Another thing: do you know if your compilation uses USE_LSB_TAG or
> Is it a 64bit or 32bit memory model?
> Have you tried to compile it with -DUSE_LISP_UNION_TYPE just to see if
> it hides the problem (or give some compilation warning at least)?

I'm guessing it's 32bit.  With CFLAGS="-g -O2 -DUSE_LISP_UNION_TYPE",
there were no suspicious compiler warnings (non at all for intervals.c)
and it still hit the intervals.c:794 breakpoint.

> > I can understand not being able to see i0 in intervals_equal, but I
> > don't understand not being able to see prev and newi in the caller.
> > tried to reproduce this with CFLAGS="-g -DENABLE_CHECKING=1
> > -DSYSTEM_PURESIZE_EXTRA=1300000", ie, no optimisation, but could not
> > reproduce the abort (or call of error).
> The fact that you don't get the assertion failure when compiling
> optimizations indicates that this assertion failure is unlikely to
> be a fluke, tho the "CHECK (!INT_LISPLIKE (i)" thingy is fishy.
> The fields of the i1 interval don't seem to be valid (0x8 can't be
> a left pointer, the right point seems to be misaligned (maybe it's
> actually a string and the up_obj bit should be set), total_length and
> position could only make sense in a buffer of at least 5-6MB).
> Then again, we have no idea if we're really looking at i1 and
> its contents.
> > Do you think these ENABLE_CHECKING aborts are genuine?
> Maybe.
> > Could there be a problem with the definition of NULL_INTERVAL_P (I
> > its definition has changed)?
> The INT_LISPLIKE thingy is fishy.  I suspect that it may misfire (the
> "struct interval" may have size 28, so intervals pointers may not all
> aligned on multiples of 8, which implies that an interval pointer may
> have the same tag bits as a buffer).
> > So, ENABLE_CHECKING not withstanding, it appears to be a problem
> > the optimisation of intervals.c itself.
> > Any other thoughts?
> Not really.  If you can reproduce it without optimizations, 
> then you may
> be able to track it down more precisely and figure out if it's
> a compiler bug or an Emacs bug.

Thanks for the suggestions and the careful reading of my report.  Is
there anything else you think I could try, eg, to deal with the size of
struct interval?  I can confirm that it is 28, though it is 28 with or
without optimisation.  I tried padding it to 32 by adding a dummy int to
it, but it still hit the breakpoint with optimisation.

I don't like the thought of trying to break up intervals.c, to binary
search for a particular problem function, so any other suggestions are


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