RockOS/kernel/syscall.S

.code32 
.global syscall_handler
.extern syscall
syscall_handler: 
    cli

    push $0
    push $0x80

    pusha

    push %ds
    push %es
    push %fs
    push %gs

    mov $0x10, %ax               
    mov %ax, %ds
    mov %ax, %es
    mov %ax, %fs
    mov %ax, %gs
    
    push %esp
    call syscall
    add $4, %esp
    
    mov 28(%esp), %eax

    pop %gs
    pop %fs
    pop %es
    pop %ds

    popa
    add $8, %esp
    iret