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Index > Macroinstructions > AT&T nested macros to FASM: solving 'symbol already defined'

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raoul



Joined: 03 Aug 2021
Posts: 2
raoul 04 Aug 2021, 00:10
Hi,

For further learning after 'Hello World', I am attempting a remake of JonesForth, originally writen in GAS. I am stuck on translating the following, where the defvar macro passes its arguments to a nested defcode macro:

Code:
        .macro defcode name, namelen, flags=0, label
        .section .rodata
        .align 4
        .globl name_\label
name_\label :
        .int link               // link
        .set link,name_\label
        .byte \flags+\namelen   // flags + length byte
        .ascii "\name"          // the name
        .align 4                // padding to next 4 byte boundary
        .globl \label
\label :
        .int code_\label        // codeword
        .text
        //.align 4
        .globl code_\label
code_\label :                   // assembler code follows
        .endm

        .macro defvar name, namelen, flags=0, label, initial=0
        defcode \name,\namelen,\flags,\label
        push $var_\name
        NEXT
        .data
        .align 4
var_\name :
        .int \initial
        .endm
    


... with example uses:

Code:
defcode "XOR",3,,XOR    // bitwise XOR
        pop %eax
        xorl %eax,(%esp)
        NEXT

defvar "S0",2,,SZ
    


My attempts that result in:

Quote:
Error: symbol already defined << link dd name_SZ >> forth.asm


Code:
macro defcode nm,namelen,flags:0,label {
section 'rodata' readable
align 8
name_#label#:
 link dd name_#label
 db flags + namelen
 db `nm
align 8
label#:
 dd code_#label
section 'text' readable executable
code_#label#:
}

macro defvar name,namelen,flags:0,label,initial:0 {
defcode name,namelen,flags,label
 push var_#name
 NEXT
section 'data' readable writable
align 8
var_#name#:
 dd initial
}
    


I tried to sprinkle some 'local' declarations, which modifies the error without improving my understanding of the issue at hand. Would you please help a beginner? Thanks!
Post 04 Aug 2021, 00:10
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 19263
Location: In your JS exploiting you and your system
revolution 04 Aug 2021, 03:01
The label "link" is being defined for each invocation of defcode.

You don't appear to be using that label so you can remove it:
Code:
name_#label#:
 dd name_#label  ; <-- no need to put the 'link' label here
 db flags + namelen    
Post 04 Aug 2021, 03:01
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raoul



Joined: 03 Aug 2021
Posts: 2
raoul 04 Aug 2021, 07:30
Ah yes, thank you! I was so fixated on the 'name_#label' part that I forgot about the 'link' part.

Now, I have another error but clearly I don't understand the code well enough because 'link' is used elsewhere, so back to studying I guess! :-S
Post 04 Aug 2021, 07:30
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