On at 2025-02-25 19:16 +0100, Danilo Pecher via Freedos-devel wrote:
Actually the first snippet looks a bit dodgy to me. Why initialize one
pointer and not the other?
If you'd actually looked into the source text for this [1] you would
have found quickly that the other pointer *is* already initialised
before it is ever read [2]. (Beat to it by Bernd pointing out the same
line in a list reply.) I wanted to fix the crash bug, not uselessly
shuffle around working code so it would please someone's aesthetic
sensibilities more than it did before.
It almost looks like someone just wanted to
make his patch look a bit more substantial than it really is.
Actually, if you knew anything about this problem, like by having read
the commit message, you may have noticed that _her_ patch is actually
complete and functional, both necessary and sufficient to address the
bug. You can easily check this yourself, for instance using this Debug
script that I created just for you. Works both in lDebug and MSDebug (my
MS-DOS v2 Debug fork), don't forget to save with CR LF line endings or
it won't work in MSDebug:
=== bug.sld
f 100 l 40 90
a
mov ah, 4A
mov bx, 1000
int 21
xor ax, ax
xchg ax, [2C]
mov es, ax
mov ah, 49
int 21
mov ah, 48
xor bx, bx
int 21
jc 140
dec ax
mov ds, ax
mov word [1], 8
mov word [8], 4453
and word [A], 0
mov ax, 4C00
int 21
a 140
mov ax, 4CFF
int 21
n testmem1.com
r bx
0
r cx
45
w 100
q
===
Run like DEBUG < bug.sld to create the TESTMEM1.COM executable. Try out
the FreeDOS MEM /D command without my patch and observe that it doesn't
crash nor loop infinitely. Then run TESTMEM1. Now run MEM /D again, and
observe that it either crashes or loops infinitely.
So there's an upside to your reply: I found out that if the empty SD MCB
isn't the first SD MCB, then it seems like there will be an infinite
loop repeating eg "EMMXXXX0 installed DEVICE=EMS" (in the local dosemu2
+ FreeDOS) forever. If the empty SD MCB is the first SD MCB, then the
crash or hang will occur at the point this SD MCB is displayed, after
the line reading "<segment> 0 (0K) DOS system data" and after an
incomplete line that reads "0000 0 (0K) ".
Regards,
ecm
[1]:
https://gitlab.com/FreeDOS/base/mem/-/blob/ce7a4c67b7304e0fb75192023c102ec0b020c38c/SOURCE/MEM/MEM.C#L1657
[2]:
https://gitlab.com/FreeDOS/base/mem/-/blob/ce7a4c67b7304e0fb75192023c102ec0b020c38c/SOURCE/MEM/MEM.C#L1677
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