[9fans] replica bug

[rod@hemiola.co.uk]

The replica utilities use an avl tree to store sets of filenames and
attributes. When new trees are created, the function "mkavltree" is
called. It's argument is the comparison routine "entrycmp" in db.c.
"entrycmp" in turn uses "strcmp" to do it's donkey work, and returns
that value directly.  The avl code requires that it's comparison
function returns -1, 0 or 1.  Strcmp is guaranteed only to return an
integer whose sign reflects the comparison result. Whilst on the 386
strcmp does indeed return -1, 0 or 1, on the arm platform this isn't
necessarily the case, leading to bad things.

in db.c:

60a61
> 	int r;
64c65,66
< 	return strcmp(ea->name, eb->name);
---
> 	r = strcmp(ea->name, eb->name);
> 	return r > 0 ? 1 : r < 0 ? -1 : 0;

Rod

;-----------------

PS. Subsequently I wondered if this problem occured elsewhere in the
system. The only other place I can find avl trees being used is in
venti/copy. The actual avl library is used here, rather than the
nearly-the-same-as-the-library file that the replica utilities use.
The function "scoretreecmp" does seem to me to have the potential to
return non (-1,0,1) values. The return value can derive not only from
memcmp, but also from the difference between the two score types.  As
it happens "memcmp" is "safe" for both 386 and arm, and I am guessing
that the latter comparison rarely happens. I also note anyway that the
avl tree is only created and used if the undocumented -m option is
specified on the command line.  It seems that the chance of provoking
the problem here is small...