[BUG?] virtual directive and labels prefixed with a dot

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chris

Joined: 05 Jan 2006
Posts: 62
Location: China->US->China->?

chris 21 Jul 2006, 03:20

Hi, Tomasz I find a possible virtual directive bug.

Code:

        jmp     .label_1 ; ok
        jmp     .label_2 ; undefined symbol error

.label_1:

        virtual at eax
          p dd ?
        end virtual

.label_2:

when compiling above code, I got undefined symbol error at "jmp .label_2", but for labels not prefixed with a dot or defined before the virtual directive, it is all right. It seems an opaque global label is defined by virtual and .lable_2 is attached to it. I am using fasm 1.67.5, could you look into this problme, thanks.

21 Jul 2006, 03:20

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 21 Jul 2006, 03:25

"p" is a label too and since it is located between "jmp .label_2" and ".label_2:" .label_2 is out of scope for that JMP. To get access to it before the definition of "p" use p.label_2 (jmp p.label_2).

Regards

21 Jul 2006, 03:25

UCM

Joined: 25 Feb 2005
Posts: 285
Location: Canada

UCM 21 Jul 2006, 17:15

Or, you could change the definition of "p dd ?" to "..p dd ?" which would not make it change the current scope, but would allow it to be accessed globally as ..p

21 Jul 2006, 17:15

Reverend

Joined: 24 Aug 2004
Posts: 408
Location: Poland

Reverend 22 Jul 2006, 12:57

But "p" is declared between "virtual" and "end virtual". Logically ".label_2" should not be attached to "p". In my opinion it is not maybe a bug, but unwanted bahaviour surely, and should be fixed.

22 Jul 2006, 12:57

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8354
Location: Kraków, Poland

Tomasz Grysztar 22 Jul 2006, 13:32

The behavior is very straightforward (and such defined in manuals): "local" label get attached to the nearest preceding it "global" label in the source (in the actual preprocessed source text). This gives the simple interpretation for the cases like:

Code:

a:
if x=3
 virtual
end if
 b dd ?
if x=4
 end virtual
end if
.c:

Code:

a:
if x=3
 b:
end if
.c:

The last label is "b.c" no matter how and whether the "b" gets actually defined. This is at least easily determinable and is utilized by some of the macros.

PS. The same goes for the anonymous labels (@@).

22 Jul 2006, 13:32

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 24 Jul 2006, 06:55

Quote:

PS. The same goes for the anonymous labels (@@).

interesting, never realized it:

Code:

jmp @f ;ERROR - undefined symbol
if 0
@@:
end if
@@:

24 Jul 2006, 06:55

chris

Joined: 05 Jan 2006
Posts: 62
Location: China->US->China->?

chris 25 Jul 2006, 09:58

Quote:

"p" is a label too and since it is located between "jmp .label_2" and ".label_2:" .label_2 is out of scope for that JMP. To get access to it before the definition of "p" use p.label_2 (jmp p.label_2).

yes, that's what I thought where the problem is.

Quote:

Or, you could change the definition of "p dd ?" to "..p dd ?" which would not make it change the current scope, but would allow it to be accessed globally as ..p

I just did it in my source to void this conflicts, and use .p also works in this case.

Quote:

But "p" is declared between "virtual" and "end virtual". Logically ".label_2" should not be attached to "p". In my opinion it is not maybe a bug, but unwanted bahaviour surely, and should be fixed.

That's what I originally wanted to say, I used the virtual directive to define some lable to access the data field of a struct, and when compiling, I got the error, so, may be we should usually use double-dotted lables inside virtual directives.

Quote:

The behavior is very straightforward (and such defined in manuals): "local" label get attached to the nearest preceding it "global" label in the source (in the actual preprocessed source text). This gives the simple interpretation for the cases like:

Quote:

[/code]
jmp @f ;ERROR - undefined symbol
if 0
@@:
end if
@@:
[/code]

thank you guys, got it. Very Happy

[/code]

25 Jul 2006, 09:58

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