El 11/04/2010 8:37, Jesus Sanchez escribis:
quoted text
>
>> i don't think so. Use gdb and see where you are writing to.
>>
>> Based on your description of your a.c and b.c, I assume in a.c you
>> have "char foo;" (global), and in b.c you by mistake have "extern int
>> foo;".
>>
>> If your foo variable is at address, say 0x11111111, and you write two
>> bytes to that address, where foo is in fact a char (single byte), the
>> other byte will be written to address 0x11111112.
>>
>> You can test this with a simple example program, where you can declare
>> other char variables around your foo variable and print all of them
>> after the foo assignment and see which ones got clobbered.
>>
>> Then again, maybe I'm misunderstanding your initial problem, you
>> didn't show your code.
>>
>> --patrick
>>
>>
>> Breakpoint 1, main (argc=1, argv=0xfffc8c8c) at a.c:30
>> 30              bar();
>> (gdb) p&f
>>  = (int *) 0x1842116
>> (gdb) x/4b 0x1842116
>> 0x1842116<f>:  0x00    0x00    0x00    0x00
>> bar () at b.c:14
>> 14              f = 0x44332211;
>> (gdb) n
>> 16      }
>> (gdb) x/4b 0x1842116
>> 0x1842116<f>:  0x44    0x33    0x22    0x11
>> (gdb) p&g
>>  = 0x1842117 "3\"1"
>> (gdb) p&k
>>  = 0x1842119 "1"
>> (gdb) p&l
>>  = 0x1842118 "\"1"
>> (gdb) p/x f
>>  = 0x44332211
>> (gdb) p/x g
>>  = 0x33
>> (gdb) p/x l
>>  = 0x22
>> (gdb) p/x k
>>  = 0x11
>>
>> Looks like the "extern int foo;" confused gdb.
>>
>
> I'm not using extern for the variables, anyway
> here is the code (to a extremely basic level) using your hint about
> making more char variables around foo to show them later:
>
> all compiled with gcc -Wall -W without warning
>
> ---------- a.c      ------------------------------------------
> #include <stdio.h>
>
> char foo;
> char foo1;
> char foo2;
> char foo3;
>
> void overfoo(); /* the func that will overflow the foo variable */
>
> int main(){
>
>    overfoo(); /* after calling we have 0x2211 on foo variable */
>
>    printf("%x\n",foo);
>    printf("%x\n",foo1);
>    printf("%x\n",foo2);
>    printf("%x\n",foo3);
>    return 0;
> }
>
> ---------- b.c      ------------------------------------------
>
> int foo; /* here the problem begins */
>
> void overfoo(){
>    foo=0x2211;
> }
>
> ---------------------------------------------------------------
>
> after compiling and executing , foo showed 0x11 and other 0x0.
>
> thanks for your time.
> -J