From mboxrd@z Thu Jan  1 00:00:00 1970
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Date: Mon, 16 Jan 2012 14:30:02 +0200
Message-ID: <CAJ1xhMUwAqtCmJSh3xUVVWS0fhAj4py2LtMfbeVuai2k2o3hzg@mail.gmail.com>
From: Alexander Kapshuk <alexander.kapshuk@gmail.com>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
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Subject: Re: [9fans] assembly syntax in plan 9
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i have a question about putting things on the stack for x86 arch under plan
9...

under unix/linux, when defining a function, i would:
(1). push the address the base pointer is pointing to prior to this
function being called, onto the stack; e.g. pushl %ebp
(2). then i would have the base pointer point to the current stack pointer;
e.g. movl %esp, %ebp
(3). then i would allocate space on the stack for local variables, if any;
e.g. subl $n, %esp;
(4). then follows the function body;
to return from the function i would:
(1). restore the stack pointer; e.g. movl %ebp, %esp;
(2). restore the base pointer, e.g. popl %ebp;
(3). then return to the calling function;

i searched the 9fans archives for posts on assembly programming under plan
9; found some bits and pieces; e.g. in one of the posts it was mentioned
that BP is a general purpose register, not the base pointer; and that FP is
what ebp is under unix/linux;

in the paper for the plan 9 assembler, it says that there are three
registers available to manipulate the stack, FP, SP, and TOS; would the
following comparison stand true then?
plan9    unix/linux
-------     -------------
FP        EBP
SP        -4(%EBP)...-n(%EBP) /* local variables */
TOS     ESP

thanks;

sasha kapshuk

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i have a question about putting things on the stack for x86 arch under plan=
 9...<div><br></div><div>under unix/linux, when defining a function, i woul=
d:</div><div>(1). push the address the base pointer is pointing to prior to=
 this function being called, onto the stack; e.g. pushl %ebp</div>
<div>(2). then i would have the base pointer point to the current stack poi=
nter; e.g. movl %esp, %ebp</div><div>(3). then i would allocate space on th=
e stack for local variables, if any; e.g. subl $n, %esp;</div><div>(4). the=
n follows the function body;</div>
<div>to return from the function i would:</div><div>(1). restore the stack =
pointer; e.g. movl %ebp, %esp;</div><div>(2). restore the base pointer, e.g=
. popl %ebp;</div><div>(3). then return to the calling function;</div><div>
<br></div><div>i searched the 9fans archives for posts on assembly programm=
ing under plan 9; found some bits and pieces; e.g. in one of the posts it w=
as mentioned that BP is a general purpose register, not the base pointer; a=
nd that FP is what ebp is under unix/linux;</div>
<div><br></div><div>in the paper for the plan 9 assembler, it says that the=
re are three registers available to manipulate the stack, FP, SP, and TOS; =
would the following comparison stand true then?</div><div>plan9 =A0 =A0unix=
/linux</div>
<div>------- =A0 =A0 -------------</div><div>FP =A0 =A0 =A0 =A0EBP</div><di=
v>SP =A0 =A0 =A0 =A0-4(%EBP)...-n(%EBP) /* local variables */</div><div>TOS=
 =A0 =A0 ESP</div><div><br></div><div>thanks;</div><div><br></div><div>sash=
a kapshuk</div><div>
<br></div>

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