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

From: H. Peter Anvin
Date: Mon Jul 16 2007 - 05:15:21 EST


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
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/