Messages in this thread | | | Date | Mon, 16 Jul 2007 11:02:01 +0200 (CEST) | From | Etienne Lorrain <> | Subject | RE : Re: RE : Re: x86 setup code rewrite in C - revised |
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--- "H. Peter Anvin" <hpa@zytor.com> wrote: > >>>> - 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 > > > > That is on Trident cards, old card but may still be used, and BIOS may have > > been copied to other cards. > > Detected and documented on Gujin (boot.c and vgabios.h scroll) > > Are you talking about BP or DS? As I said, the BP is well-known, and > the code accounts for it in the form of the INT10 macro.
Extract of RBIL61: INT 10 - VIDEO - SCROLL UP WINDOW AH = 06h AL = number of lines by which to scroll up (00h = clear entire window) BH = attribute used to write blank lines at bottom of window CH,CL = row,column of window's upper left corner DH,DL = row,column of window's lower right corner Return: nothing Note: affects only the currently active page (see AH=05h) BUGS: some implementations (including the original IBM PC) have a bug which destroys BP the Trident TVGA8900CL (BIOS dated 1992/9/8) clears DS to 0000h when scrolling in an SVGA mode (800x600 or higher)
Scrolling is only (and automatically) done if the cursor is at bottom right.
> >>>> 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. > > > > strange, "g" would mean anything can go there - and this assembly instruction > > should accept every access modes. > > Not with an %fs: prefix. It would also allow the compiler to do a move > into a register "on its own", which would be disastrous, since it would > lack the prefix. So "m" is correct.
"mov %fs:(%ebx,%eax,4),%ecx" works for me.
Etienne.
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