Hi!
17--2006 03:05 [EMAIL PROTECTED] (Michael Devore) wrote to
freedos-devel@lists.sourceforge.net:
>> >> May you explain here and/or, better, in comments in source, why
>> >> decreasing SP solves issues (and which issues there are)?
>> >>>Only plausible explanation: THIS BIOS damages (sometimes ?) the flags;
>> >> Do you mean "flags, _saved on the stack above given code_"?
>> >> And, if so, then why flags are damaged, but return value, which was lies
>> >> on place of flags (relative SP) are not damaged, if you comment out
>> >> "pushf"?
>>that's all I know. this ugly patch solves the issue.
But how you found this?! And what you found? Do you found (with help of
debugger?), that "popf" restores not the same value, as "pushf"? And do you
try to disasm BIOS INT15 entry to check, what precisely "damages" flags?
More details, please!
>>looks like sometimes someone damages something on the stack, which
>>goes unnoticed most of the time
Unless found precise reason, there are no assurance, that your patch
fixes (not masks) anything and not damages anything else.
>> > Could just be hitting one word on the stack, i.e. [sp] at INT entry. That
And? Why return address isn't damaged? Let me ask again:
stack:
| ret address |
+-------------+
| pushf | <- tom thinks, this value damaged
+-------------+
| INT15 call |
stack after tom's patch:
stack:
| ret address | <- why this value not damaged?
+-------------+
| INT15 call |
>> > would match the behavior on either of the two patches.
>>right
No: in first case stack lesser, in second case it deeper.
MD> Plus, I just found out that there exist old compressed DOS programs which
MD> avoid the automatic A20 handling of the kernel,
Which packer (and/or programs, which packed by this/these packers)? How
"avoid"? There is only one (implicit) way for this: call some DOS service
before executing decompression.
MD> and try to directly use
MD> address wrapping, so there's no way to automatically avoid the "packed file
MD> is corrupt" termination with high free memory
More details, please!
MD> In other words, those old
MD> programs must use LOADFIX or other workarounds to run. I'm still waiting
MD> for some good news to come in.
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