Re: is this a bug ?

[Jonathan James <jonathan () SECURITO SE>]

Guy,
No this isn't a bug, you are forcing the CPU into an infinite loop..
First you jump to "start" where the "call doit" instruction is passed.
When the CPU has executed the instructions at label "doit" it will continue
to execute whatever follows, i.e label "start" again which
just jumps back to label "doit".

Kindest Regards
Jonathan James

> Hello,
>
> first i mast explain i am no programmer, i just read a few documents
> on the web and try to play with stuff. If this is inappropriate here
> please tell me and except my apologize.
>
> anyhow,
> i have this asm code:
>
> .global id
> .global end
> .data
> id:
>         jmp start
> doit:
>         popl %esi
>         movl %esi,0x08(%esi)
>         xorl %eax,%eax
>         movb %eax,0x07(%esi)
>         movl %eax,0xc(%esi)
>
>         movb $0xb,%eax
>         movl %esi,%ebx
>         leal 0x8(%esi),%ecx
>         xorl %edx,%edx
>         int  $0x80
>
> start:
>         call doit
>         .string "/bin/idX"
> end:
>
> and the c to run it:
> extern void id();
> extern void end();
> main()
> {
>   id();
> }
>
> both a ripof from Marc Blumenauer <marc () system-security net>
>
> but what strikes me odd is that if i cange any of the length of the string
> to a wrong lenght (0x09 for example)  my cpu get to 98.8 usage % after 5
> seconds. (this is run by regular user)
>
> Can any one explain/verify this on a computer with more the 133MHz and 48
RAM ?
> Cheers,
>
> Guy