#
# fork-test: Tests the fork system call.
#
# 1. Calls SYS_FORK
# 2. Parent prints "Parent: pid=<pid>\n" and waits for child
# 3. Child prints "Child: pid=0\n" and exits with code 7
# 4. Parent exits with code 0
#

.section .text
.global _start

# System call numbers
.equ SYS_EXIT,    0
.equ SYS_WRITE,   1
.equ SYS_FORK,    3
.equ SYS_GETPID,  4
.equ SYS_WAITPID, 6

_start:
    # Fork
    movl $SYS_FORK, %eax
    int $0x80

    # EAX = 0 in child, child PID in parent
    testl %eax, %eax
    jz .child

.parent:
    # Save child PID on the stack
    pushl %eax

    # Print "Parent\n"
    movl $SYS_WRITE, %eax
    movl $1, %ebx              # fd = stdout
    movl $parent_msg, %ecx
    movl $parent_msg_len, %edx
    int $0x80

    # Waitpid for child
    popl %ebx                  # child PID
    movl $SYS_WAITPID, %eax
    int $0x80
    # EAX now has child's exit code (should be 7)

    # Print "Reaped\n"
    pushl %eax                 # save exit code
    movl $SYS_WRITE, %eax
    movl $1, %ebx
    movl $reaped_msg, %ecx
    movl $reaped_msg_len, %edx
    int $0x80
    popl %ebx                 # exit code (unused, exit with 0)

    # Exit with code 0
    movl $SYS_EXIT, %eax
    movl $0, %ebx
    int $0x80

.child:
    # Print "Child\n"
    movl $SYS_WRITE, %eax
    movl $1, %ebx              # fd = stdout
    movl $child_msg, %ecx
    movl $child_msg_len, %edx
    int $0x80

    # Exit with code 7
    movl $SYS_EXIT, %eax
    movl $7, %ebx
    int $0x80

.section .rodata
parent_msg:     .ascii "Parent\n"
.equ parent_msg_len, . - parent_msg
child_msg:      .ascii "Child\n"
.equ child_msg_len, . - child_msg
reaped_msg:     .ascii "Reaped\n"
.equ reaped_msg_len, . - reaped_msg