Re: A20 delay

[Quality Quorum <qqi@world.std.com>]

On 16 Dec 1999, Ian Lance Taylor wrote:

>    Date: Wed, 15 Dec 1999 23:40:01 -0500 (EST)
>    From: Quality Quorum <qqi@world.std.com>
> 
>    >    BTW, gas still does not like 'jnz $1b' .
>    > 
>    > I'd be happy to look at a test case.
> 
>    Apply patch, replace `more:' with `1:' and `jnz more' with `jnz $1b'
> 
> First, I made a mistake talking about $1b.  Temporary dollar labels
> use a trailing '$'.  The expression $1b refers to the label 1b as an
> immediate value.
> 
> It helps a lot to talk about a specific test case.  You gave me
> instructions, but I might be starting from the wrong file, or I might
> follow the instructions incorrectly, or I might misinterpret the
> result.
> 
> So, to be precise:
> 
> This test case:

This is precisely what I had.

> 
> 	movl    $0x200, %eax
> 1:	dec     %eax
> 	jnz     $1b
> 	ret
> 
> fails, as I expect it to.  jnz does not take an immediate operand.  I
> get this error message:
> 
> /home/ian/foo.s:3: Error: suffix or operands invalid for `jnz'
> 
> 
> This test case:
> 
> 	movl    $0x200, eax
> 1:	decl    eax
> 	jnz     1b
> 	ret
> 
> appears to succeed.
> 
>    > Note that gas supports two different conventions for local variables:
>    > the dollar sign convention and the numeric f/b convention.  If you are
>    > literally using `jnz $1b' then you are mixing them, which won't work.
> 
>    I am really puzzled, because there a few places  in pc386 where various 
>    forms of 
> 
> 	 jz $1f
>    1:
> 
>    are both assembled without a hitch and seems working ok.
> 
> Again, a specific test case helps.  I could not find any code in pc386
> matching your description.  It may be there even though I was unable
> to find it.
> 
> I did find this case:
> 
> 	ljmpl	$0x08, $1f
> 1:
> 
> This is not a branch instruction.  In gas syntax, the two operand ljmp
> instruction takes an immediate operand.  $1f is an immediate operand
> referring to the label 1f.


Wow, how lucky I am that I only occasinally have to do this stuff.
BTW, is it documented somewhere ? I would be able to fiure it 
out on my own in year.

> 
> To see this, this test case fails:
> 
> 	ljmpl	$0x08, foo
> foo:	
> 
> while this test case succeeds:
> 
> 	ljmpl	$0x08, $foo
> foo:	
> 
> If you really have a test case which uses
> 	 jz $1f
>    1:
> and which succeeds, please send it to me.
> 
> Ian
> 

Thanks,

Aleksey