Chuck Ebbert wrote:
>> Have fun, this code:
>> - do not open the fast A20 gate before checking if the slow A20 gate is open or closed.
As does the current code; this is highly intentional behaviour since
there are machines (in particular a whole series of machines made by
Olivetti) which lock up if you do it differently.
>> - uses in asm("") inputs which may or may not be set by the compiler in the stack,
>> after modifying the stack pointer in the asm block: at least has_eflag()
Point. "g" should be "ri". I will send a patch.
>> - The VGA recalc has the same bug as the assembly version where a VGA write protected
>> register is written (Overflow register) without setting the enable bit (see VGA docs).
OK, that would be a bug ported directly from the assembly version. The
fact that the bug can be seen now is part of why I did this work.
Please feel free to submit a patch.
>> - Does not save and restore %ds when printing a char on the screen (%ds is destroyed
>> only when the content of the screen scroll - only for some video cards)
%ds? Aren't you confusing it with the old bug which would destroy %bp?
If you have any references to %ds being destroyed I would be very
surprised. I can guarantee that very little if any assembly code I've
ever seen that deals with INT 10h -- and I've seen a lot of it -- guards
against %ds being randomly trashed.
However, the trashing of %bp is a well-known bug (although only for
machines older than the ones that can run Linux) -- the Interrupt List has:
BUGS: some implementations (including the original IBM PC) have a bug
which destroys BP
>> - Has a "dn" for outl() which sliped in instead of "dN"
That's a bug, although currently nonmanifest -- there are no users of
outl() at the present. I will send a patch.
>> and probably few other problems - just seen those by reading the patches (the asm("")
>> are inlined in the C code - I find it more difficult to check).
>>
>> Also, I do not know if "m" is right in here:
>> static inline u8 rdfs8(addr_t addr)
>> {
>> u8 v;
>> asm("movb %%fs:%1,%0" : "=r" (v) : "m" (*(u8 *)addr));
>> return v;
>> }
The "m" is correct right there.
>> I may repeat me, but to find these kind of problems, it is very nice to have an ELF
>> file to do a readelf/objdump -D -m i8086 (even after final link).
There is such a file (arch/i386/boot/setup.elf) which is retained, for
exactly this reason.
-hpa
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