mmap and string operations in assembler

Question

I am trying to code something that allocates some memory for a string and fills that memory with random characters. Now I decided to go the way of mmap-syscalls, without using malloc functions.

Here is my code:

.code32
.data
    random: .ascii "/dev/random\0"

.section .data
    c: .ascii "t"   #just a test static character, for test
    n: .ascii "\n"  #end of string
.text
    .global _start
    _start:


pushl $0    # offset of 0
pushl $-1 # the file handle of the open file
pushl $33     # MAP_SHARED flag set to write changed data back to file
pushl $3     # PROT_READ and PROT_WRITE permissions
pushl $42   
pushl $0     # Allow the system to select the location in memory to start
movl %esp,%ebx   # copy the parameters location to EBX
movl $90,%eax    # set the system call value
int $0x80
movl %eax,%edi  #the adress of allocated memory is stored in edi
pushl %eax  #save the adress on stack 
movl $42, %ecx  #now i want to generate 42 random symbols and print them
loop:
    dec %ecx        
    pushl %ecx                              #generate a random number, using the kernel Entropy Collector
    movl $5,%eax                            # sys_open
    movl $random,%ebx                       # Filename string

    movl $0,%ecx      # O_RDONLY flag
    int $0x80
                                    # Read one random number
    movl %eax,%ebx     # The result of sys_open
    movl $3,%eax       # sys_read
    movl (%esp),%ecx     # The stack is our buffer
    movl $1,%edx       # 
    int $0x80       #random number on stack
    popl %eax       #eax represents the random number
    movl $100,%ebx
    divl %ebx       #modulo 223
    leal 34(%edx),%eax
    stosb           #load a random char into allocated memory           
    popl %ecx
    cmpl $0,%ecx
    jne loop

movl $4,%eax        #syscall write
movl $1,%ebx
movl $43,%edx
popl %ecx       #pop the saved adress of string
int  $0x80

movl $1,%eax        #exit
int $0x80

`

which causes a segfault in MOVSB - operation.

So I am not sure about a couple of things:

1. The way I just push integers between 33 and 255 to ESI before the MOVSB, hoping that the integer will be recognized as an ascii sign, for which it stands.
2. The way I allocate memory
3. Also not quite sure about the correctness of the LEAL - operation, which aims to just move through the allocated (42??) bytes of memory each time jumping to a new byte. Although this one can not cause the segfault as it comes after the error-causing MOVSB.

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##### EDIT: Stack faults fixed by setting correct flags in mmap-call and changing movsb to stosb