Re: entry16.inc code doubt

Hi,

I checked the pentium manuals, could not find any reference
to these statements as listed below.
> > andl $0x7FFAFFD1, %eax /* PG,AM,WP,NE,TS,EM,MP = 0 */
> > orl $0x60000001, %eax /* CD, NW, PE = 1 */

The syntax for and is reverse 
and <register> <immediate value>
Whereas the code reads 
andl <immediate value> <register>

Could someone please help me on this or redirect to
exact reference for the above statements.

Regards
Deepak
> you really need to get a pengium manual.

Where do I get this one. Is it some Linux Man Page.
Could you please give me the link where I can look for
it.

Thanks and Regards
Deepak

----- Original Message ----- 
From: "ron minnich" 
To: 
Cc: 
Sent: Monday, April 21, 2003 9:34 PM
Subject: Re: entry16.inc code doubt
> On Mon, 21 Apr 2003 [e-mail] wrote:
> > ***Extract***
> > andl $0x7FFAFFD1, %eax /* PG,AM,WP,NE,TS,EM,MP = 0 */
> > orl $0x60000001, %eax /* CD, NW, PE = 1 */
>
> you really need to get a pengium manual.
>
> Then it will all make sense.
>
> ron
>
> Linuxbios mailing list
> [e-mail]
> http://www.clustermatic.org/mailman/listinfo/linuxbios

_______________________________________________
Linuxbios mailing list
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entry16.inc code doubt

[Peter Stuge]

On Tue, Apr 22, 2003 at 12:17:08PM +0500, [e-mail] wrote:
> I checked the pentium manuals, could not find any reference
> to these statements as listed below.
> > > andl $0x7FFAFFD1, %eax /* PG,AM,WP,NE,TS,EM,MP = 0 */
> > > orl $0x60000001, %eax /* CD, NW, PE = 1 */
>
> The syntax for and is reverse 
> and <register> <immediate value>
> Whereas the code reads 
> andl <immediate value> <register>
>
> Could someone please help me on this or redirect to
> exact reference for the above statements.

Hi.

The two instructions you quote are taken out of context and are by
themselves completely meaningless.

They are mere bit operations on registers:
andl performs a bitwise AND of a register (the eax register, in this case)
and the 0x7ffaffd1 immediate value, and stores the result back into the
register.
orl performs a bitwise OR of a register (again eax) and the 0x60000001
immediate value, and stores the result back into eax.

Before these two instructions I'm guessing that there is a line reading
mov %eax, cr0

and following them, there is a line reading
mov cr0, %eax

(cr0 above may also be %cr0, I'm more familiar with intel assembly syntax.)

Now, this puts the bit mangling in a totally different perspective.  cr0 is
the Configuration Register 0, which among other things contains the PE bit,
as indicated by the comment following the or instruction.  PE controls
whether the CPU is in protected mode or not.

To connect the dots for you, your two instructions combined with my two
instructions will set a number of different flags in cr0, among other
things switching the CPU to protected mode if not already in it.

Hope this helps, and gives a few pointers.

//Peter

entry16.inc code doubt

[steven james]

Greetings,

What you're seeing is the difference between Intel syntax (used in their
assemblers) and AT&T syntax used in the GNU assembler. The big differences
are that the operands are reversed, and the mnemonic (opcode) explicitly
refers to the operand size by appending one of b, w, or l for byte, word,
or long (1, 2, or 4 bytes).

G'day,
sjames

On Tue, 22 Apr 2003 [e-mail] wrote:
> Hi,
>
> I checked the pentium manuals, could not find any reference
> to these statements as listed below.
> > > andl $0x7FFAFFD1, %eax /* PG,AM,WP,NE,TS,EM,MP = 0 */
> > > orl $0x60000001, %eax /* CD, NW, PE = 1 */
>
> The syntax for and is reverse 
> and <register> <immediate value>
> Whereas the code reads 
> andl <immediate value> <register>
>
> Could someone please help me on this or redirect to
> exact reference for the above statements.
>
> Regards
> Deepak
> > you really need to get a pengium manual.
>
> Where do I get this one. Is it some Linux Man Page.
> Could you please give me the link where I can look for
> it.
>
> Thanks and Regards
> Deepak
>
> ----- Original Message ----- 
> From: "ron minnich" 
> To: 
> Cc: 
> Sent: Monday, April 21, 2003 9:34 PM
> Subject: Re: entry16.inc code doubt
> > On Mon, 21 Apr 2003 [e-mail] wrote:
> > > ***Extract***
> > > andl $0x7FFAFFD1, %eax /* PG,AM,WP,NE,TS,EM,MP = 0 */
> > > orl $0x60000001, %eax /* CD, NW, PE = 1 */
> >
> > you really need to get a pengium manual.
> >
> > Then it will all make sense.
> >
> > ron
> >
> > Linuxbios mailing list
> > [e-mail]
> > http://www.clustermatic.org/mailman/listinfo/linuxbios
>
> Linuxbios mailing list
> [e-mail]
>
> Linuxbios mailing list
> [e-mail]
> http://www.clustermatic.org/mailman/listinfo/linuxbios

entry16.inc code doubt

[ron minnich]

On Tue, 22 Apr 2003 [e-mail] wrote:
> I checked the pentium manuals, could not find any reference
> to these statements as listed below.
> > > andl $0x7FFAFFD1, %eax /* PG,AM,WP,NE,TS,EM,MP = 0 */
> > > orl $0x60000001, %eax /* CD, NW, PE = 1 */

You need to learn how to read Gnu Assembler. This is GNU assembly code.

ron