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Date: Mon, 24 Jun 2002 13:46:00 -0000
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Subject: optimization/7108: gcc 3.1 initialize two times the same variable
X-SW-Source: 2002-06/txt/msg00569.txt.bz2
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>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: