the final weeks of fasm 1.67

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Helle

Joined: 24 Feb 2007
Posts: 23
Location: Germany

Helle

Hello,
in "ADD r/m64, imm32" gives an (unsigned) value of imm32 >= 80000000h an "error:value out of range" (also "ADD RAX, imm32", and also ADC, AND, CMP, OR, SBB, SUB, XOR; other not tested). I think, a value up to 0FFFFFFFFh is correct. Intel wrote only: "sign-extended to 64-bits", but not a restriction of imm32.
Thanks!
Helle

28 Apr 2009, 14:30

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17865
Location: In your JS exploiting you and your system

revolution

You can't have unsigned 64bit values above 0x7fffffff in an imm32 value. This is not an error, there is no way to encode such values in the x86-64 instruction set.

28 Apr 2009, 14:49

MazeGen

Joined: 06 Oct 2003
Posts: 977
Location: Czechoslovakia

MazeGen

In other words, opcode 480500000080 means ADD RAX, 0FFFFFFFF80000000h, it is not ADD RAX, (00000000)80000000h.

28 Apr 2009, 15:22

Helle

Joined: 24 Feb 2007
Posts: 23
Location: Germany

Helle

Hmm, but the CPU accept this e.g.:

Code:

mov rax,0
dw 0548h
dd 0D0000000h  ;ADD RAX,0D000000h

The result is FFFFFFFFD0000000h, like expected. With the restriction I never get the sign-extension.

Thanks!
Helle

28 Apr 2009, 19:25

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4633
Location: Argentina

LocoDelAssembly

What about:

Code:

xor eax, eax ; 31 C0
add rax, -30000000h ; 48 05 00 00 00 D0

28 Apr 2009, 21:04

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 7845
Location: Kraków, Poland

Tomasz Grysztar

Or:

Code:

add rax, 0FFFFFFFFD0000000h

29 Apr 2009, 06:15

Helle

Joined: 24 Feb 2007
Posts: 23
Location: Germany

Helle

Hello,
you are right. It´s for a disassembler-project and I make tests with udis86; this shows ADD RAX,0xD0000000h. I will use your Code, it´s better for eyes and brain Very Happy

!
Solved, sorry and thanks!
Helle

29 Apr 2009, 09:35

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4633
Location: Argentina

LocoDelAssembly

Tomasz Grysztar wrote:

Or:

Code:

add rax, 0FFFFFFFFD0000000h

Because I think that one should also say "value out of range" (also for "alpha = 0FFFFFFFFD0000000h"). Razz

Reason:

Code:

add rax, 0FFFFFFFFD0000000h / 10000h ; add rax, -3000h
add eax, 0FFFFD000h / 10000h         ; add eax, 0FFFFh

add rax, 18446744072904245248 / 65536 ; add rax, -3000h

29 Apr 2009, 14:23

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17865
Location: In your JS exploiting you and your system

revolution

See here also.

29 Apr 2009, 15:16

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 7845
Location: Kraków, Poland

Tomasz Grysztar

LocoDelAssembly wrote:

Code:

add rax, 0FFFFFFFFD0000000h / 10000h ; add rax, -3000h
add eax, 0FFFFD000h / 10000h         ; add eax, 0FFFFh

add rax, 18446744072904245248 / 65536 ; add rax, -3000h

That's perfectly correct as long as you know, that in fasm "/" is always equivalent to 64-bit IDIV. The revolution has made a good point there, however adding such sign bit into fasm would not be a quick task (though possible, so I may consider it for some future releases).

29 Apr 2009, 16:32

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4633
Location: Argentina

LocoDelAssembly

Quote:

That's perfectly correct as long as you know, that in fasm "/" is always equivalent to 64-bit IDIV.

Does TFM say that? Wink

But yet, it would be better not do that way as if you decide in the future to extend to 128-bit internal precision (or even arbitrary), you'll be forced to break backward compatibility.

29 Apr 2009, 18:22

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17865
Location: In your JS exploiting you and your system

revolution

LocoDelAssembly: 128bit!? Do you think that CPUs will have 128bit arithmetic any time soon? SSE/AVX use 64bit operations.

29 Apr 2009, 18:26

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4633
Location: Argentina

LocoDelAssembly

Quote:

128bit!? Do you think that CPUs will have 128bit arithmetic any time soon?

Absolutely:

Code:

mov ecx, 7
div rcx ; 128-bit dividend

29 Apr 2009, 18:34

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17865
Location: In your JS exploiting you and your system

revolution

LocoDelAssembly wrote:

Absolutely:

Code:

mov ecx, 7
div rcx ; 128-bit dividend

Hehe, but not really 128bit is it. In x86-128 ISA you would have "div wcx ;256 bit dividend".

29 Apr 2009, 18:45

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 7845
Location: Kraków, Poland

Tomasz Grysztar

LocoDelAssembly wrote:

But yet, it would be better not do that way as if you decide in the future to extend to 128-bit internal precision (or even arbitrary), you'll be forced to break backward compatibility.

This cannot be done with fasm 1.x architecture.
And the fasm 2 is going to be incompatible with 1.x anyway, so it's not a big deal. Wink

29 Apr 2009, 20:39

comrade

Joined: 16 Jun 2003
Posts: 1137
Location: Russian Federation

comrade

Is FASM2 going to be coded in asm? Or in something sane? Smile

30 Apr 2009, 03:27

r22

Joined: 27 Dec 2004
Posts: 805

r22

FASM2 should have javascript macros.

That would be fun.

comrade is right! FASM2 should be created in a HEX EDITOR Tomasz has got it way too easy with his mnemonics for machine code Very Happy

30 Apr 2009, 20:55

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