Message-ID:	<000801be4d5f$66931660$9fbc98ce@waldroni>
From:	"Isaac Waldron" <waldroni AT lr DOT net>
To:	"Eli Zaretskii" <eliz AT is DOT elta DOT co DOT il>
Cc:	<djgpp AT delorie DOT com>
Subject:	Re: Accessing Constants in Assembly Code
Date:	Sun, 31 Jan 1999 16:19:33 -0500
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Reply-To:	djgpp AT delorie DOT com

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- -----Original Message-----
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
To: Isaac Waldron <waldroni AT lr DOT net>
Cc: djgpp AT delorie DOT com <djgpp AT delorie DOT com>
Date: Sunday, January 31, 1999 2:42 AM
Subject: Re: Accessing Constants in Assembly Code


>
>On Sat, 30 Jan 1999, Isaac Waldron wrote:
>
>> 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'
>
>Use the `nm' program (it's part of Binutils and should be already in
>your `bin' subdirectory) to see how does the compiler mangles the
name
>of VideoRAM, then make sure the assembly source references the
mangled
>name.
>
>Alternatively, declare VideoRAM ``extern "C"'', which disables
>mangling.

I executed this command:

gxx -S mode13.cc

and looked at the resulting mode13.s.

Here's the block from mode13.s that appears to define VideoRAM:

LFE3:
.lcomm _VideoRAM,4
    .section .ctor
    .long   __GLOBAL_$I$_screen_width
.text
    .p2align 2
.globl __GLOBAL_$I$_screen_width
__GLOBAL_$I$_screen_width:
LFB4:
    pushl %ebp
LCFI124:
    movl %esp,%ebp
LCFI125:
    pushl $40960
LCFI126:
    call ___dpmi_segment_to_descriptor
    movl %eax,_VideoRAM
    leave
    ret

So, the symbol _VideoRAM (which points to a 4-byte area of the data
segment) should be able to be accesed from my assembler code as
_VideoRAM, right?

Thanks again,
Isaac Waldron

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