NASM externs and Microsoft LINK?

[vLK]

Hello!
I am quite new to NASM, for some time I've used FASM (NASM syntax is a bit scary for beginners), but in general, I'm also quite new to ASM.

At the moment, I am mostly playing around with this assembler to learn its syntax fully. Much of it I like, and it's been pretty straight forward so far, although this morning I encountered a problem with WinAPI imports and I hope that you can help me..

So.. I'm declaring an extern using the obvious 'extern' directive:

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extern SleepIn my code I then call this a couple of times, this is not very important, it assembles nicely with:

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nasm -f win32 -Ox -o code.obj code.s
However when I try to link with this line, using Microsoft LINK, all hell is let loose:

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link /ENTRY:main /SUBSYSTEM:console /MACHINE:X86 kernel32.lib code.obj
code.obj : error LNK2001: unresolved external symbol Sleep
code.exe : fatal error LNK1120: 1 unresolved externals
I have tried declaring the symbol _Sleep, __imp__Sleep and __imp__Sleep@4 but it generates the same error.

What am I doing wrong here? Should I maybe just use another linker? Anyone else had these problems?

And another question: Whats the essential difference between a %define and an equ? Is there any differences but the one that equ supports various expressions? Hope I don't appear too nooby Thanks!

[Keith Kanios]

I have tried declaring the symbol _Sleep, __imp__Sleep and __imp__Sleep@4 but it generates the same error.

You pretty much danced around it. IIRC, the STDCALL decoration for that function should be: _Sleep@4

And another question: Whats the essential difference between a %define and an equ? Is there any differences but the one that equ supports various expressions? Hope I don't appear too nooby Thanks!

As per NASM Doc Section 3.2.4, an equ is for assigning constants, thus it is only evaluated once and cannot be changed.

As per NASM Doc Section 4.1.1, a define is a single-line macro, thus it is apart of the preprocessor, can be changed and may be evaluated multiple times.

[vLK]

That worked! Thank you for your answers

[Frank Kotler]

A subtle difference between "%define" and "equ" is that a symbol assigned with "equ" goes into the symbol table, and makes it into the executable (at least in Linux). This may have advantages. A symbol defined with "%define" is an "assemble-time only" symbol - no trace of it in the executable (AFAIK).

You could think of "equ" as a "numeric cut-and-paste" and "%define" as a "text cut-and-paste"... (I think...).

Out of curiousity, vLK, what parts of Nasm syntax do you find scary, compared to Fasm?

Best,
Frank

[Keith Kanios]

Out of curiousity, vLK, what parts of Nasm syntax do you find scary, compared to Fasm?

I'm curious too, as FASM is basically a fusion of TASM and NASM concepts that were favored by the author.