From: Paul Riley <paul@rileyriot.com>
To: tuhs <tuhs@minnie.tuhs.org>
Subject: Re: [TUHS] Using printf from Assembly Language in V6, and db.
Date: Mon, 28 Jun 2021 13:27:51 +1000 [thread overview]
Message-ID: <CAD05_j1xY-XOPA2xeMcP-kZs5a41EDfiRQezOf_YAgGbOdjqtA@mail.gmail.com> (raw)
In-Reply-To: <CAD05_j0NUPk70gbMEgXM7bNJfVkALKxHBbT87d+K=T3DxbF_1Q@mail.gmail.com>
[-- Attachment #1: Type: text/plain, Size: 2688 bytes --]
Or perhaps...
In my example, the substitutional arguments for printf are pushed onto the
> stack in reverse order, then the address of the string, and then printf is
> called. After this, 6 is added to the stack pointer. I assume that the
> printf routine pops the address of the string off the stack, but leaves the
> other values on the stack, hence the need to add 2x3=6 to the stack after
> calling printf in my example.
>
... just adding 2 for every decrement that was done on sp...
Paul
*Paul Riley*
Mo: +61 (0)411 781 394
Email: paul@rileyriot.com
On Mon, 28 Jun 2021 at 12:34, Paul Riley <paul@rileyriot.com> wrote:
> Hi,
>
> I want to use printf from an assembly language program, in V6. It seems
> that the Unix Programmer's Manual doesn't show how to use it from assembly,
> so I wrote a short C program and captured the assembler output, for some
> clues. Listings below.
>
> In my example, the substitutional arguments for printf are pushed onto the
> stack in reverse order, then the address of the string, and then printf is
> called. After this, 6 is added to the stack pointer. I assume that the
> printf routine pops the address of the string off the stack, but leaves the
> other values on the stack, hence the need to add 2x3=6 to the stack after
> calling printf in my example.
>
> What troubles me is that the stack pointer is not decremented before the
> first mov, in the example below. Is this some C convention? I would assume
> that the first push in my example would overwrite the top of the stack.
> Perhaps I'm not used to PDP-11 stack conventions.
>
> I understand db only works on files like a.out or core dumps. If I wanted
> to break the assembly language program to examine values, how can I force a
> termination and core dump elegantly, so I can examine some register values?
>
> Paul
>
>
> *Paul Riley*
>
> Email: paul@rileyriot.com
>
> int a, b, c;
> int main(){
> printf("printf: start\n");
> a = 1;
> b = 2;
> c = 3;
> printf("A = %d, B = %d, C = %d", a, b, c);
> printf("printf: end\n");
>
> }
>
> .comm _a,2
> .comm _b,2
> .comm _c,2
> .globl _main
> .text
> _main:
> ~~main:
> jsr r5,csv
> jbr L1
> L2:mov $L4,(sp)
> jsr pc,*$_printf
> mov $1,_a
> mov $2,_b
> mov $3,_c
> mov _c,(sp)
> mov _b,-(sp)
> mov _a,-(sp)
> mov $L5,-(sp)
> jsr pc,*$_printf
> add $6,sp
> mov $L6,(sp)
> jsr pc,*$_printf
> L3:jmp cret
> L1:jbr L2
> .globl
> .data
> L4:.byte 160,162,151,156,164,146,72,40,163,164,141,162,164,12,0
> L5:.byte
> 101,40,75,40,45,144,54,40,102,40,75,40,45,144,54,40,103,40,75,40,45,144,0
> L6:.byte 160,162,151,156,164,146,72,40,145,156,144,12,0
> #
>
>
[-- Attachment #2: Type: text/html, Size: 4168 bytes --]
next prev parent reply other threads:[~2021-06-28 3:29 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-28 2:34 Paul Riley
2021-06-28 3:27 ` Paul Riley [this message]
2021-06-28 4:48 Noel Chiappa
2021-06-28 11:27 ` Paul Riley
2021-06-28 13:48 ` Clem Cole
2021-06-28 20:37 Noel Chiappa
2021-06-29 12:18 ` Paul Riley
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAD05_j1xY-XOPA2xeMcP-kZs5a41EDfiRQezOf_YAgGbOdjqtA@mail.gmail.com \
--to=paul@rileyriot.com \
--cc=tuhs@minnie.tuhs.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).