From: "Isaac Waldron" <waldroni AT lr DOT net>
Newsgroups: comp.os.msdos.djgpp
Subject: Accessing Constants in Assembly Code
Date: Sat, 30 Jan 1999 15:23:09 -0500
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To: djgpp AT delorie DOT com
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First off, here's the output from gcc -v:

C:\waldroni\projects\graphics>gcc -v
Reading specs from c:/djgpp/lib/specs
gcc version 2.8.1

OK, now I would like to know how to access a constant that is declared
in a .cc file with assembly language.  I use NASM to create my object
files from .s files.  I have a constant called VideoRAM that is
declared in a .cc file with this syntax:

const int VideoRAM = __dpmi_segment_to_descriptor(0xA000);

I want to be able to access this constant through an assembly routine
called _BlitPage, defined as follows:

*** file blit.s ***
extern _drawBuffer
extern _VideoRAM

segment .text

global _BlitPage
_BlitPage:
    push ebp
    mov ebp,esp
    mov eax,[_VideoRAM]
    mov es,ax
    xor edi,edi
    mov esi,_drawBuffer
    mov ecx,32000
    rep movsw
    leave
    ret

*** end of file ***

Now, when these two files are compiled and placed in libgraphics.a, a
graphics library I'm writing, things appear ok.  But, the compile dies
at the linking stage with the following error:

C:\waldroni\projects\graphics>gxx -o testc.exe testc.cc -lgraphics
c:/djgpp/lib/libgraphics.a(blit.o)(.text+0x4):../src/blit.s: undefined
reference to `VideoRAM'

Has anyone else had this problem?

Thanks in advance,
Isaac Waldron


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