> As a die-hard assembly language programmer, I was very pleased when recently
> someone posted a link to his Hello, World assembly language code here.
I did that as a die-hard pascal programmer: -) This is one of those things every
non C programmer runs into.
> I played with his code a bit, then wrote a very simple filter in assembly
> language. I then converted it to an article on System Calls in FreeBSD,
> and submitted it to Assembly Programming Journal, which is a bi-monthly
> on-line magazine.
>
> If anyone is interested, the text of the article (includes the code for
> the filter) is at http://www.whizkidtech.net/syscall.txt
>
> I pose a question in it (where can an assembly language program find its
> command line): If anyone knows the answer, I'd love to hear it!
Locate directory csu (I believe it is in /usr/src/lib/csu),
and compile crt0.c with -S and -O3 or so. (which simplifies the assembler)
(I believe this won't work with a recent compiler, I had to do it on a system
with a 2.7.x compiler)
You will find something like the following code in it like this:
(The U_SYSLINUX labels are Free Pascal variables that are loaded, I had to
'fix' crt0 for that)
movl %edx,%edx
#NO_APP
leal 8(%ebp),%edi
movl %edi,U_SYSLINUX_ARGV
mov -4(%edi),%eax
movl %eax,U_SYSLINUX_ARGC
movl 4(%ebp),%ebx
leal 12(%ebp,%ebx,4),%esi
movl %esi,U_SYSLINUX_ENVP
movl %esi,environ
testl %ebx,%ebx
jle .L2
movl 8(%ebp),%eax
testl %eax,%eax
je .L2
movl %eax,__progname
cmpb $0,(%eax)
je .L2
Well, argv, argc, the enviroment, what more can you want :-)
Anyway, the generated assembler source will also reveal how to parse that
structure. You can also rip out all libc initialisation code (or I can sent you
my version, in which you only have to comment those U_SYSLINUX lines)
if you don't link to libc.
Marco van de Voort ([EMAIL PROTECTED])
<http://www.stack.nl/~marcov/xtdlib.htm>
Marco van de Voort ([EMAIL PROTECTED])
<http://www.stack.nl/~marcov/xtdlib.htm>
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