[TUHS] as(1) on Ultrix-11 vs 2.11BSD
Clem Cole
clemc at ccc.com
Fri May 1 08:06:16 AEST 2020
Alexander, the exit(2) system call takes a parameter, which is an integer
status that the process will return. The value 0 is traditionally a
successful return, and anything else signifies an error condition.
This assembler is the moral equiv of:
char hello[] = { "hello world\n" };
main() {
write(1, hello, sizeof(hello));
exit(0);
}
On Thu, Apr 30, 2020 at 5:50 PM Alexander Voropay <alec at sensi.org> wrote:
> Can anyone please explain the last $0 pushed to the stack ?
> Early SysIII ans SYSV on the i386 (and may be on i286) used
> similar syscall convention.
>
> I wrote about this:
> https://minnie.tuhs.org/pipermail/tuhs/2019-October/019274.html
> https://minnie.tuhs.org/pipermail/tuhs/2019-October/019294.html
>
> Example:
> ===
> .file "test.s"
> .version "02.01"
> .set WRITE,4
> .set EXIT,1
> .text
> .align 4
> .globl entry
> entry:
> pushl %ebp
> movl %esp,%ebp
> subl $8,%esp
>
> pushl $14 /length
> pushl $hello
> pushl $1 /STDOUT
> pushl $0
> movl $WRITE,%eax
> lcall $0x07,$0
> addl $16,%esp
>
> pushl $0
> movl $EXIT,%eax
> lcall 0x07,$0
>
> .data
> .align 4
> hello:
> .byte 0x48,0x65,0x6c,0x6c,0x6f,0x2c, 0x20,0x77,0x6f,0x72
> .byte 0x6c,0x64,0x21,0x0a,0x00
>
> ср, 29 апр. 2020 г. в 17:19, <ron at ronnatalie.com>:
> >
> > Thanks for the link. With that help, I fixed the bug in the program:
> >
> > mov $6., -(sp)
> > mov $1f, -(sp)
> > mov $1,-(sp)
> > mov $0,-(sp)
> > sys 4
> > add $8., sp
> > mov $0,-(sp)
> > mov $0,-(sp)
> > sys 1
> > 1: <hello>
> >
> >
> > >> Sorry, I typed that in haste without testing. I don’t have a 2.11
> system
> > >> to try it on. However, reading the source code, I did that wrong. The
> > >> args go on the stack, not in line with the code.
> > >> mov $6, -(sp)
> > >> mov a, -(sp)
> > >> mov $1,-(sp)
> > >> sys 4
> > >
> > > Without suggesting that every helpful post should be tested, I find the
> > > superb https://unix50.org web emulator excellent for such things.
> > >
> > > Many thanks to the folks hosting & maintaining this great resource!
> > >
> > >
> >
> >
>
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