Re: optimization/7108: gcc 3.1 initialize two times the same variable

Re: optimization/7108: gcc 3.1 initialize two times the same variable

[-=Quequero=-]

The following reply was made to PR optimization/7108; it has been noted by GNATS.

From: -=Quequero=- <quequero@linux.bitchx.it>
To: rth@gcc.gnu.org,gcc-bugs@gcc.gnu.org,gcc-prs@gcc.gnu.org,
 nobody@gcc.gnu.org,quequero@linux.bitchx.it,gcc-gnats@gcc.gnu.org
Cc:  
Subject: Re: optimization/7108: gcc 3.1 initialize two times the same
  variable
Date: Thu, 04 Jul 2002 14:21:45 +0200

 At 00.33 04/07/2002 +0000, you wrote:
 >    Since you clearly didn't turn on optimization, what did you
 >     expect?
 >
 >http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=7108
 yes i know optimization is off in my example...btw, optimization or not, 
 initializing two times
 the same variable is always unuseful...I have reported this _bug_ only for 
 that :)
 thanx a lot
 
 -=Quequero=-
 SpP/Member www.spippolatori.com
 UIC Founder www.quequero.cjb.net
 Linux Registered User #207978
 Slackware User #12573
 

Re: optimization/7108: gcc 3.1 initialize two times the same variable

[rth]

Synopsis: gcc 3.1 initialize two times the same variable

State-Changed-From-To: open->closed
State-Changed-By: rth
State-Changed-When: Wed Jul  3 17:33:43 2002
State-Changed-Why:
    Since you clearly didn't turn on optimization, what did you
    expect?

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=7108

optimization/7108: gcc 3.1 initialize two times the same variable

[quequero]

>Number:         7108
>Category:       optimization
>Synopsis:       gcc 3.1 initialize two times the same variable
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    unassigned
>State:          open
>Class:          pessimizes-code
>Submitter-Id:   net
>Arrival-Date:   Mon Jun 24 13:46:01 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     gcc 3.1 Thread model: single
>Release:        3.1
>Organization:
>Environment:
Linux 2.4.18 #16 Tue May 28 14:07:34 CEST 2002 i686
>Description:
Look here:
void function(char *string){
        char buffer[100];
        int i=0;
        ....

Now, let's disassemble it (i have used stripped and non-stripped version of the executable):

.text:08048492                 push    ebp
.text:08048493                 mov     ebp, esp
.text:08048495                 sub     esp, 98h
.text:0804849B                 mov     [ebp+i], 0
.text:080484A2                 mov     [ebp+i], 0

the same variable is initiaziled twice :)
>How-To-Repeat:
i've discovered it compiling a silly program that i'm writing for a demonstration:

void overflow(char *string);
int main(int argv, char *argc[]){
        overflow(argc[1]);
}
void overflow(char *string){
        char buffer[100];
        int i=0;
        for(i=0; i<=100; i++)
                buffer[i] = string[i];
        printf("Typed: %s\n", buffer);
}

the disassembling the funciot "overflow" with IDA:
.text:0804849B                 mov     [ebp+i], 0
.text:080484A2                 mov     [ebp+i], 0
i can see that "int i" is initialized twice to 0 but as you can see ebp doesn't change so that instruction shouldn't be there :P
>Fix:
i really don't know
>Release-Note:
>Audit-Trail:
>Unformatted: