Re: Buffers in Assembly (NASM)

On Sat, 19 Jul 2008 11:53:43 GMT, NoSpam@xxxxxxxxxxx (Bob Masta)
wrote:

On Sat, 19 Jul 2008 02:18:33 -0500, ArarghMail807NOSPAM
<spamtrap@xxxxxxxxxx> wrote:

On Fri, 18 Jul 2008 19:34:08 -0700 (PDT), "bwaichu@xxxxxxxxx"
<spamtrap@xxxxxxxxxx> wrote:

I'm trying to better understand data structures in assembly. I know I
can create a zero filled buffer in the bss section in NASM with this:

The bss section is by definition not initialized by the program, so
you have to clear it yourself.

Not familiar with NASM or its linker, but with MASM32 and the standard
PE linker the BSS section (called .data? in MASM) is automatically
zeroed. In this section you can not specify a fill value, you must
use ? or MASM reports an error, but when the app runs that section is
always filled with zeros.

I did a little digging, and found that for DOS type programs written
in C, the bss is cleared by the C runtime startup code. For windows
programs written in C, there is no clearing routine in the startup
code, so windows must have zeroed it out. (Assumption, not necessarily
a good one!)

So for an assembler program, for DOS, you have to clear bss yourself,
for windows, you can try assuming that windows did it.

But I clear it out, anyway. It's only done once at the beginning of
the program, and that way I *KNOW* it has been zeroed out.
--
ArarghMail807 at [drop the 'http://www.' from ->] http://www.arargh.com
BCET Basic Compiler Page: http://www.arargh.com/basic/index.html

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