Operating Systems 2022F: Assignment 1

This Assignment is still being developed.

/* 3000menu.c */
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdlib.h>

extern char **environ;

char *menu[] = {
        "/usr/bin/ls",
        "/usr/bin/whoami",
        "/usr/bin/top",
        "QUIT",
        NULL
};

int QUIT = 3;

void run_program(int choice)
{
        pid_t pid;
        int status;
        
        printf("Running %s\n", menu[choice]);

        pid = fork();

        if (pid == 0) {
                menu[choice+1] = NULL;
                execve(menu[choice], menu + choice, environ);
                exit(-1);
        } else {
                pid = wait(&status);
        }
        
        return;
}

int choose_program(void)
{
        int i = 0;
        int choice;
        char *input = NULL;
        size_t result, n = 0;

        printf("\nChoose a program to run:\n\n");
        
        while (menu[i] != NULL) {
                printf("%d. %s\n", i + 1, menu[i]);
                i++;
        }

        printf("\nYour choice? ");

        result = getline(&input, &n, stdin);

        choice = atoi(input);

        if ((choice > 0) && (choice <= i)) {
                return choice - 1;
        } else {
                return -1;
        }
}

int main()
{
        int program;

        while (1) {
                program = choose_program();

                if (program == QUIT) {
                        return 0;
                }
                
                if (program != -1) {
                        run_program(program);
                }
        }
}

<syntaxhighlight lang="asm" line .file "3000menu.c" .text .section .rodata.str1.1,"aMS",@progbits,1 .LC0: .string "Running %s\n" .text .globl run_program .type run_program, @function run_program: .LFB51: .cfi_startproc endbr64 pushq %rbx .cfi_def_cfa_offset 16 .cfi_offset 3, -16 subq $16, %rsp .cfi_def_cfa_offset 32 movl %edi, %ebx movq %fs:40, %rax movq %rax, 8(%rsp) xorl %eax, %eax movslq %edi, %rdx leaq menu(%rip), %rax movq (%rax,%rdx,8), %rdx leaq .LC0(%rip), %rsi movl $1, %edi movl $0, %eax call __printf_chk@PLT call fork@PLT testl %eax, %eax je .L5 leaq 4(%rsp), %rdi call wait@PLT movq 8(%rsp), %rax subq %fs:40, %rax jne .L6 addq $16, %rsp .cfi_remember_state .cfi_def_cfa_offset 16 popq %rbx .cfi_def_cfa_offset 8 ret .L5: .cfi_restore_state leaq menu(%rip), %rax leal 1(%rbx), %edx movslq %edx, %rdx movq $0, (%rax,%rdx,8) movslq %ebx, %rbx leaq (%rax,%rbx,8), %rsi movq (%rax,%rbx,8), %rdi movq environ(%rip), %rdx call execve@PLT movl $-1, %edi call exit@PLT .L6: call __stack_chk_fail@PLT .cfi_endproc .LFE51: .size run_program, .-run_program .section .rodata.str1.1 .LC1: .string "\nChoose a program to run:\n" .LC2: .string "%d. %s\n" .LC3: .string "\nYour choice? " .text .globl choose_program .type choose_program, @function choose_program: .LFB52: .cfi_startproc endbr64 pushq %r13 .cfi_def_cfa_offset 16 .cfi_offset 13, -16 pushq %r12 .cfi_def_cfa_offset 24 .cfi_offset 12, -24 pushq %rbp .cfi_def_cfa_offset 32 .cfi_offset 6, -32 pushq %rbx .cfi_def_cfa_offset 40 .cfi_offset 3, -40 subq $40, %rsp .cfi_def_cfa_offset 80 movq %fs:40, %rax movq %rax, 24(%rsp) xorl %eax, %eax movq $0, 8(%rsp) movq $0, 16(%rsp) leaq .LC1(%rip), %rdi call puts@PLT movq menu(%rip), %rcx testq %rcx, %rcx je .L12 movl $1, %ebx leaq .LC2(%rip), %r13 leaq -8+menu(%rip), %r12 .L9: movl %ebx, %ebp movl %ebx, %edx movq %r13, %rsi movl $1, %edi movl $0, %eax call __printf_chk@PLT addq $1, %rbx movq (%r12,%rbx,8), %rcx testq %rcx, %rcx jne .L9 .L8: leaq .LC3(%rip), %rsi movl $1, %edi movl $0, %eax call __printf_chk@PLT leaq 16(%rsp), %rsi leaq 8(%rsp), %rdi movq stdin(%rip), %rdx call getline@PLT movl $10, %edx movl $0, %esi movq 8(%rsp), %rdi call strtol@PLT testl %eax, %eax jle .L13 cmpl %eax, %ebp jl .L13 subl $1, %eax .L7: movq 24(%rsp), %rdx subq %fs:40, %rdx jne .L16 addq $40, %rsp .cfi_remember_state .cfi_def_cfa_offset 40 popq %rbx .cfi_def_cfa_offset 32 popq %rbp .cfi_def_cfa_offset 24 popq %r12 .cfi_def_cfa_offset 16 popq %r13 .cfi_def_cfa_offset 8 ret .L12: .cfi_restore_state movl $0, %ebp jmp .L8 .L13: movl $-1, %eax jmp .L7 .L16: call __stack_chk_fail@PLT .cfi_endproc .LFE52: .size choose_program, .-choose_program .globl main .type main, @function main: .LFB53: .cfi_startproc endbr64 subq $8, %rsp .cfi_def_cfa_offset 16 .L19: call choose_program cmpl %eax, QUIT(%rip) je .L22 cmpl $-1, %eax je .L19 movl %eax, %edi call run_program jmp .L19 .L22: movl $0, %eax addq $8, %rsp .cfi_def_cfa_offset 8 ret .cfi_endproc .LFE53: .size main, .-main .globl QUIT .data .align 4 .type QUIT, @object .size QUIT, 4 QUIT: .long 3 .globl menu .section .rodata.str1.1 .LC4: .string "/usr/bin/ls" .LC5: .string "/usr/bin/whoami" .LC6: .string "/usr/bin/top" .LC7: .string "QUIT" .section .data.rel.local,"aw" .align 32 .type menu, @object .size menu, 40 menu: .quad .LC4 .quad .LC5 .quad .LC6 .quad .LC7 .quad 0 .ident "GCC: (Ubuntu 11.2.0-19ubuntu1) 11.2.0" .section .note.GNU-stack,"",@progbits .section .note.gnu.property,"a" .align 8 .long 1f - 0f .long 4f - 1f .long 5 0: .string "GNU" 1: .align 8 .long 0xc0000002 .long 3f - 2f 2: .long 0x3 3: .align 8 4: </syntaxhighlight>