Hi, I would like to spread some fear, uncertainity and distrust
about EBDA movement!
For explanation, in 2032+ kernels, this is enabled by default.
You can suppress it with SWITCHES=/E in your config sys file.
Some time ago, I noticed that UPX would sometimes create broken,
truncated, cross-linked... files, but could never reproduce it.
That was with kernel 2032a as far as I remember.
Today I had the same with kernel 2034 when trying to compile MODE.
In DOSEMU, things worked fine, but not in plain FreeDOS. The
UPXed file would crash or would even cross-link to cluster 0 (good
that the kernel now shows a warning when it hits such a broken
cluster chain).
Removing LBAcache would not change the situation. But guess what,
adding SWITCHES=/E to my config apparently fixed the problem!
Interesting: My 2032a troubles a while ago and 2034 troubles now
happened on different computers with different BIOS brands (the
2034 test was done on a PC with a BIOS in Windows style design
with a mouse pointer which wiggles its tail all the time X-)).
If you take my problems on 2 different computers and the problems
described for a third computer in Bugzilla on:
http://www.freedos.org/bugs/bugzilla/show_bug.cgi?id=1771
Then you can conclude that EBDA movement can be generally dangerous.
Maybe NOT moving EBDA could be made the default? If the EBDA is not
moved, there are less than 640k of DOS memory. Some programs might
fail to notice that and accidentally overwrite the EBDA at the end
of the last 640k. On the other hand, moving the EBDA can be missed
by some instances in BIOS(es) which means that when FreeDOS thinks
that the last part of the first 640k can be used by DOS again SOME
other software still writes EBDA data there. In bug 1771, the
effect was overwriting the MCB at 9fff:0 which broke UMB operation
whenever EBDA was moved.
I think it is somehow hard to decide what is more dangerous - NOT
moving the EBDA (less than 640k DOS RAM) or MOVING the EBDA (into
some low memory location allocated by DOS). For now, I think it is
safer to leave the EBDA unmoved.
Eric.
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