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Index > Compiler Internals > small bug ?

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ouadji



Joined: 24 Dec 2008
Posts: 1081
Location: Belgium
ouadji
Code:
(fasm 1.69.12)

A)
--
db 0,\" 
1
extra characters on line (line 1) ..... ok

B-1)
---
db 0,\a
1
illegal instruction (line 2) ..... ??
instruction : 1

but ... with a space between "\" and "a", it's ok.

B-2)
---
db 0,\ a
1
extra characters on line (line 1) .... ok
    

A) and B-2)

in this two cases, "extra characters on line"
the answer is correct and logical.
PS : in "A)", it's ok, with or without space between "\" and ' " '

B-1)

Without space between "\" and 'a', there is a problem.
Question the answer should it not also be "extra characters on line"
and not "illegal instruction", opcode instruction : 1

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Post 25 Feb 2010, 09:57
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
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revolution
A bit of a cosmetic bug. You still get some sort of error that is the main thing.
Post 25 Feb 2010, 15:24
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Tomasz Grysztar



Joined: 16 Jun 2003
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Tomasz Grysztar
The "\" character in fasm has a different function when immediatelly followed by a symbol token, and different when not. In the first case it creates the "escaped" symbol ("\a" in this sample), and in second case it marks the ignored line break and no other symbols should follow in the same line.
Post 25 Feb 2010, 15:38
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Tomasz Grysztar



Joined: 16 Jun 2003
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Tomasz Grysztar
PS You may notice that this is a perfectly valid code, because "\a" is a valid symbol:
Code:
\a:
  mov ax,\a    
Post 25 Feb 2010, 15:40
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ouadji



Joined: 24 Dec 2008
Posts: 1081
Location: Belgium
ouadji

Thank you for your reply. I understood your explanation.
So yes, with this difference about function of the symbol "\",
followed by a symbol token, or not ...
then I am more in agreement with the reaction of the compiler.

however, i noticed this :
Code:
FASMW
-------
\a: 
mov ax,\a   ; with ax, or eax, it does compile, it's ok. (FASMW)

FASM
-----
\a: 
mov ax,\a   ; doesn't compile : invalid use of symbol (FASM)

But with "eax", it's ok.
\a: 
mov eax,\a   ; it does compile, it's ok. (FASM)
    


@revolution : "a cosmetic bug"
I do not try to bother, but simply to understand.

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Post 25 Feb 2010, 17:00
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
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Location: In your JS exploiting you and your system
revolution
ouadji wrote:
FASM
-----
\a:
mov ax,\a ; doesn't compile : invalid use of symbol (FASM)
Code:
flat assembler  version 1.69.07  (100000 kilobytes memory)
1 passes, 3 bytes.    
Works for me.
Post 26 Feb 2010, 02:08
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bitshifter



Joined: 04 Dec 2007
Posts: 764
Location: Massachusetts, USA
bitshifter
Hmm...
I though that would put word offset of label into AX?

Also, why/how can this be legal?
Code:
\a:
mov al,\a    
Post 26 Feb 2010, 02:14
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revolution
When all else fails, read the source


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revolution
bitshifter wrote:
Hmm...
I though that would put word offset of label into AX?
It does.
bitshifter wrote:
Also, why/how can this be legal?
Code:
\a:
mov al,\a    
mov al,0
Post 26 Feb 2010, 02:42
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bitshifter



Joined: 04 Dec 2007
Posts: 764
Location: Massachusetts, USA
bitshifter
Ahhh, i get it, offset was zero...
I thought we needed to use same reg size as code.
Its legal all the way up to MAX_BYTE

Within range:
Code:
times 255 db 0
\a:
mov al,\a    

Out of range:
Code:
times 256 db 0
\a:
mov al,\a    


Thanks for the clarification Smile
Post 26 Feb 2010, 05:24
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ouadji



Joined: 24 Dec 2008
Posts: 1081
Location: Belgium
ouadji

(fasm 1.69.12)
Quote:

from revolution :Works for me.
indeed revolution, it does compile, but without "format MS COFF".

does compile
Code:
\a: 
mov ax,\a
    

this, below, does not compile
Code:
format MS COFF
\a: 
mov ax,\a
    

why ? i don't understand.

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Post 26 Feb 2010, 08:17
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revolution
When all else fails, read the source


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revolution
A good example why one should always show all of one's code when asking for help. Otherwise one gets the wrong answer.

Anyhow, does this compile for you?
Code:
format MS COFF
a: 
mov ax,a    
If not then perhaps it is something other than the backslash (\) that is causing your problem.
Post 26 Feb 2010, 08:25
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cthug



Joined: 03 Apr 2009
Posts: 36
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cthug
I am [edit]NOT[/edit] familiar with the COFF format but perhaps it uses 32bit symbols?

[edit]It has relocation, and symbol table.[/edit]


Last edited by cthug on 26 Feb 2010, 10:32; edited 1 time in total
Post 26 Feb 2010, 08:43
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ouadji



Joined: 24 Dec 2008
Posts: 1081
Location: Belgium
ouadji

this doesn't compile either !
Code:
format MS COFF ;fasm 1.69.12
nop
b:
mov ax,b    
Quote:
always show all of one's code when asking for help
agree with you, but :

my_file.asm : 3220 lines
my_file.inc : 1420 lines

Wink

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Post 26 Feb 2010, 09:35
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vid
Verbosity in development


Joined: 05 Sep 2003
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vid
Cthug is right. How exactly do you expect compiler to move relocated symbol into 16-bit register?
Post 26 Feb 2010, 11:23
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ouadji



Joined: 24 Dec 2008
Posts: 1081
Location: Belgium
ouadji

indeed, correct.
I had not thought of it ! thank you.

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Post 26 Feb 2010, 11:33
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