How to use FSAVE , FNSAVE in FASM

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3D_FASM

Joined: 11 May 2023
Posts: 24

3D_FASM 03 Jun 2023, 10:02

Example of code?

03 Jun 2023, 10:02

macomics

Joined: 26 Jan 2021
Posts: 1150
Location: Russia

macomics 03 Jun 2023, 10:07

Code:

fsave [state]
state:          db 512 dup (0)

03 Jun 2023, 10:07

3D_FASM

Joined: 11 May 2023
Posts: 24

3D_FASM 03 Jun 2023, 10:26

Why size is 512. Maybe 94 or 108 bytes?

Last edited by 3D_FASM on 03 Jun 2023, 11:20; edited 1 time in total

03 Jun 2023, 10:26

macomics

Joined: 26 Jan 2021
Posts: 1150
Location: Russia

macomics 03 Jun 2023, 11:07

Just with a margin.

I showed you how to declare a buffer. And what length it should be - choose for yourself.

The point: since fasm1 does not have a data type of a suitable length for this command, it is necessary to make a label without specifying the length of the data. I.e., use the label directive or put : after label name.

03 Jun 2023, 11:07

3D_FASM

Joined: 11 May 2023
Posts: 24

3D_FASM 03 Jun 2023, 11:22

Ok. FNSAVE instruction writes 94 bytes of data when the CPU executes 16-bit code and 108 bytes of data when the CPU executes 32-bit code.

Code:

state: db 108 dup (0) 
...
     fsave [state]

03 Jun 2023, 11:22

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20632
Location: In your JS exploiting you and your system

revolution 03 Jun 2023, 11:29

We need a fiftyfourword size operand!

Code:

state d54w ?
fsave [state]
fsave fiftyfourword[0x1234]

03 Jun 2023, 11:29

macomics

Joined: 26 Jan 2021
Posts: 1150
Location: Russia

macomics 03 Jun 2023, 11:32

revolution wrote:

We need a fiftyfourword size operand!

Cool. When did it appear? Why is there nothing about this in the documentation?

Code:

use64
fsave [state]
state d54w ?

Code:

~ $ fasm test1.asm -m 102400
flat assembler  version 1.73.30  (102400 kilobytes memory)
test1.asm [3]:
state           d54w ?
processed: state d54w ?
error: illegal instruction.

Code:

use32
fsave fiftyfourword [state]
state db 512 dup ?

Code:

~ $ fasm test1.asm -m 102400
flat assembler  version 1.73.30  (102400 kilobytes memory)
test1.asm [2]:
fsave fiftyfourword [state]
processed: fsave fiftyfourword[state]
error: invalid operand.

Last edited by macomics on 03 Jun 2023, 11:39; edited 2 times in total

03 Jun 2023, 11:32

3D_FASM

Joined: 11 May 2023
Posts: 24

3D_FASM 03 Jun 2023, 11:35

Hm... why d54w ? why not d108b ?)

fiftyfourword - sounds too long.

Last edited by 3D_FASM on 03 Jun 2023, 11:35; edited 1 time in total

03 Jun 2023, 11:35

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20632
Location: In your JS exploiting you and your system

revolution 03 Jun 2023, 11:35

macomics wrote:

Cool. When did it appear? Why is there nothing about this in the documentation?

Shh. Don't tell anyone. It is a secret.

03 Jun 2023, 11:35

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20632
Location: In your JS exploiting you and your system

revolution 03 Jun 2023, 11:36

3D_FASM wrote:

Hm... why d54w ? why not d108b ?)

It follows the normal dw, dd, dq, d54w / word, dword, qword, fiftyfourword. Perfectly sensible.

03 Jun 2023, 11:36

macomics

Joined: 26 Jan 2021
Posts: 1150
Location: Russia

macomics 03 Jun 2023, 11:42

revolution, see above

03 Jun 2023, 11:42

3D_FASM

Joined: 11 May 2023
Posts: 24

3D_FASM 03 Jun 2023, 11:43

revolution wrote:

It follows the normal dw, dd, dq, d54w / word, dword, qword

Fine but db is skipped at start of this sequence:
db - 1 byte,
dw - 2 bytes,
dd - 4 bytes,
dq - 8 bytes
etc ...

03 Jun 2023, 11:43

macomics

Joined: 26 Jan 2021
Posts: 1150
Location: Russia

macomics 03 Jun 2023, 11:47

3D_FASM wrote:

Fine but db is skipped at start of this sequence:
db - 1 byte,
dw - 2 bytes,
dd - 4 bytes,
dq - 8 bytes
etc ...

He meant

db - define byte (1 byte)
dw - define word (2 bytes)
dd - define double word (4 bytes),
dq - define qquad word(8 bytes)
etc ...
d54w - define 54 * word (54*2 bytes = 108)

03 Jun 2023, 11:47

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8397
Location: Kraków, Poland

Tomasz Grysztar 03 Jun 2023, 11:52

With fasmg's implementation you can use a sized label (but it works with unsized one as well, just like in fasm):

Code:

include 'cpu/p5.inc'

use32
fsave [state]

label state:108
rb 108

03 Jun 2023, 11:52

3D_FASM

Joined: 11 May 2023
Posts: 24

3D_FASM 03 Jun 2023, 11:53

It seems to me that a byte is quite a normal and understandable unit of measurement instead word. This is by the way.

03 Jun 2023, 11:53

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20632
Location: In your JS exploiting you and your system

revolution 03 Jun 2023, 12:35

3D_FASM wrote:

It seems to me that a byte is quite a normal and understandable unit of measurement instead word. This is by the way.

Talk to Intel about that. They started it. Smile

03 Jun 2023, 12:35

Furs

Joined: 04 Mar 2016
Posts: 2626

Furs 03 Jun 2023, 18:04

Byte should've been called half word.

03 Jun 2023, 18:04

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20632
Location: In your JS exploiting you and your system

revolution 03 Jun 2023, 23:07

Arm defines hwords as 16-bit. So byte should be quarter word.

But then there is confusion between quad word (4 x 32-bit) and quarter word (1/4 x 32-bit) Sad

Code:

my_data dq ? ; is this 8-bits or 128-bits?

03 Jun 2023, 23:07

macomics

Joined: 26 Jan 2021
Posts: 1150
Location: Russia

macomics 04 Jun 2023, 02:24

revolution wrote:

But then there is confusion between quad word (4 x 32-bit) and quarter word (1/4 x 32-bit) Sad
Code:
my_data dq ? ; is this 8-bits or 128-bits?     

Will have to make two definitions with different registers

Code:

my_data8   dq ?
my_data128 dQ ?

04 Jun 2023, 02:24

bitRAKE

Joined: 21 Jul 2003
Posts: 4227
Location: vpcmpistri

bitRAKE 04 Jun 2023, 08:35

Furs wrote:

Byte should've been called half word.

Word was defined first - before byte. At first, word meant the native size of the machine - it could be 18-bit or 30-bit; whatever the machine used.

Byte came later, 5-bit bytes and it grew - "just a part of a word" - because it was shorter than typing character.

The power of two scheme came later. Once bytes became 8-bits, nibbles were needed, and before that there was a phase where everything was defined in octal - three bit thinking. 😀

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04 Jun 2023, 08:35

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