Re: RE : Re: RE : Re: x86 setup code rewrite in C - revised

["H. Peter Anvin" <hpa@zytor.com>]

Etienne Lorrain wrote:

> 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)

"When scrolling in an SVGA mode", sounds to me like a bug when using
BIOS for text output in graphics mode.  We don't do that.

>>>>>>  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.

That's an example on what "m" can generate.

"g" could produce stuff like:

	mov %fs:$1234,%ecx
	mov %fs:%eax,%ecx

	-hpa