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From: eplmst AT lu DOT erisoft DOT se (Martin Stromberg)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Assembly Question:
Date: 11 Feb 2002 13:10:29 GMT
Organization: Ericsson Erisoft AB, Sweden
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References: <000a01c1b296$f2b0dc00$34e2a0c8 AT rjo DOT virtua DOT com DOT br> <slrna6ehga DOT 9j6 DOT kala AT ganga DOT sankya DOT com>
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To: djgpp AT delorie DOT com
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Babu Kalakrishnan (kala AT sankya DOT com) wrote:
: On Sun, 10 Feb 2002 21:56:07 -0300, Pedro Izecksohn <izecksohn AT yahoo DOT com> wrote:
: >   When "gcc asmtest.c -S" the code below:
: >
: >void test1 () {
: >}
: >
: >void main () {
: >test1();
: >}
: >
: >   gcc makes the following .S code: (Without the lines numbers.)
: >
: >12 _main:
: >13 pushl %ebp
: >14 movl %esp, %ebp
: >15 subl $8, %esp
: >16 andl $-16, %esp
: >17 call _test1
: >18 movl %ebp, %esp
: >19 popl %ebp
: >20 ret
: >21 .ident "GCC: (GNU) 3.0.3"
: >
: >   What is the purpose of the lines 15 and 16 ?

: These are obviously meant for ensuring 16 byte stack alignment. I'm not
: sure why both statements are present though. May be the first one is
: part of the entry code (to correct for the pushed return address and
: pushed ebp occupying 8 bytes) - and the second is a part of the function
: call code (ensuring 16 byte alignment before calling the function).

It there because the original poster didn't turn on optimisations. Try
with "-O2", see the difference and take note.


Right,

						MartinS