.globl _start
_start:
    # set ebp for backtrace
    movl $0x0, %ebp
# load argc and argv
movl (%esp), %ebx
lea 0x4(%esp), %ecx


# move down the esp register
# since it may cause page fault in backtrace
subl $0x20, %esp

# save argc and argv on stack
pushl %ecx
pushl %ebx

# call user-program function
call umain

1:  jmp 1b