Arkady V.Belousov wrote:
Hi!
20-Ноя-2005 16:57 [EMAIL PROTECTED] (Kenneth Davis) wrote to
[EMAIL PROTECTED]:
--- NEW FILE: intwrap.asm ---
reloc_call_int13_handler:
cli ; disable other interrupts for now
INT instruction already disables IFlag.
stc ; force error unless BIOS clears
?! This is issue of caller to set or reset CFlag.
push dx ; store BIOS drive # for error handling usage
push ds ; get segment of kernel DATA
mov ds, [cs:_DGROUP_]
pushf ; simulate int call so returns back here (flags+cs:ip on
stack)
call far [ds:_UserInt13]
Bug!!! Here DS register is garbaged, whereas it used by some functions
(for example, INT13/42).
good catch, I rewrote this section several times until I finally tracked
down my problem was my usual init-time variables don't match run-time
variables [address wise, though the compiler thinks they do, so the
UserInt13 initialized wasn't the one used] unless special care is taken.
Earlier versions had a different path for ah < 17h versus ah > 17h,
which I need to re-add (as the error values returned do not make sense
for most functions ah > 17h, but even if not returned, still within same
error code group for those less; that or just change it to check on
int13/16h )
pop ds ; restore ds
jc int13err ; test if error, if not return to caller
int13iret:
inc sp ; clean up stack
inc sp
sti ; ensure int's are renabled
retf 2 ; return to caller leaving flags asis
I don't think that this is right way, because caller may disable
interrupts for own purposes, whereas here interrupts enabled.
I'm not sure what is correct here, but I suppose it should simply leave
the flag as the user had it (I think I added this after reading a note
somewhere in RBIL about a bug in earlier BIOSes that failed to do this).
int13wrap:
%IF XCPU < 186
push ax ; preserve registers, setup stack frame
push bp
mov bp, sp
mov ax, 13h ; want to push 0x13 onto stack
xchg ax, [bp+2] ; so restore pushed ax value and put 0x13 on stack
pop bp ; clean up stack frame (leaving just 0x13 pushed on stack)
push bp
push bp
mov bp,sp
mov word [bp+2],13h
pop bp
I like it, cleaner and removes the easy to overlook restoration of ax
Thanks for reviewing these patches,
Jeremy
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