[tlbuild] m-tx test fails on powerpc-linux

[Johannes Hielscher]

> > 3) Failing that, I can only suggest running under the debugger and
> > try to discern where the bad value comes from.  
> 
> I'll have a try. Tomorrow.
> 
OK, I found the error in the m-tx code, which explains the wrong value
of fracindent. Located by some lengthy gdb fiddling.
(tl;dr: patch below)

I am no Pascal expert, but the loop ranges in preamble.pas:501ff
  for i:=1 to maxvoices do setVocal(i,false);
  for i:=1 to maxstaves do stave_size[i]:=unspec;
  for i:=0 to maxstaves do nspace[i]:=unspec;
  begin  nspace[i]:=unspec;  stave_size[i]:=unspec;  end;
are definitely inconsistent. Pascal won't switch from zero-based to
one-based arrays within a loop.

There is an array bound violation error in here. (NB nspace[] is
created with maxstaves entries!). In the C code, this is even more
obvious:
  for (i = 0; i <= maxstaves; i++)
    nspace[i] = unspec;
  nspace[i] = unspec;

In the last iteration, of the third loop, the (semantically unrelated)
variable fracindent gets overwritten, since it happens to lie at exactly
the memory address of nspace[maxstaves], at least within the
memory of the PowerPC binary:
(gdb) print &nspace[16]
$20 = (short *) 0x20060b18 <fracindent>
Note that gdb even knows this!

Other architecture probably have other memory alignments, so that the
bound violation does at least not overwrite the (somewhat
visible) fracindent variable -- but what else?

I came up with this tiny fix that makes prepmx behave correctly:

Index: Build/source/utils/m-tx/mtx-src/preamble.c
===================================================================
--- Build/source/utils/m-tx/mtx-src/preamble.c  (Revision 47364)
+++ Build/source/utils/m-tx/mtx-src/preamble.c  (Arbeitskopie)
@@ -799,7 +799,7 @@
     setVocal(i, false);
   for (i = 0; i <= maxstaves - 1; i++)
     stave_size[i] = unspec;
-  for (i = 0; i <= maxstaves; i++)
+  for (i = 0; i < maxstaves; i++)
     nspace[i] = unspec;
   nspace[i] = unspec;
   stave_size[i-1] = unspec;
Index: Build/source/utils/m-tx/mtx-src/preamble.pas
===================================================================
--- Build/source/utils/m-tx/mtx-src/preamble.pas        (Revision 47364)
+++ Build/source/utils/m-tx/mtx-src/preamble.pas        (Arbeitskopie)
@@ -500,7 +500,7 @@
   style_supplied := false; 
   for i:=1 to maxvoices do setVocal(i,false);
   for i:=1 to maxstaves do stave_size[i]:=unspec;
-  for i:=0 to maxstaves do nspace[i]:=unspec;
+  for i:=0 to maxstaves-1 do nspace[i]:=unspec;
   begin  nspace[i]:=unspec;  stave_size[i]:=unspec;  end;
   n_pages:=1; n_systems:=1;
   readStyles; old_known_styles := known_styles;

(The Pascal part of the patch is just based on an extrapolation from
the surrounding code. It should be controlled by someone who is
familiar with the intentions behind array/loop ranges in Pascal.)

BTW The code line in question was indeed introduced by m-tx v0.63 and
came into TL with SVN -r46254. I just didn't find it in the first run
because I thought that it  would be enough to search for "fracindent"
when fracindent behaves strange \-:


Thanks,
Johannes