#include <syscall-nr.h>
#include <stdio.h>
#include "tests/lib.h"
#include "tests/main.h"

/**
 * From threads/vaddr.h:
 */
#define BITMASK(SHIFT, CNT) (((1ul << (CNT)) - 1) << (SHIFT))

#define PGSHIFT 0                          /* Index of first offset bit. */
#define PGBITS  12                         /* Number of offset bits. */
#define PGSIZE  (1 << PGBITS)              /* Bytes in a page. */
#define PGMASK  BITMASK(PGSHIFT, PGBITS)   /* Page offset bits (0:12). */

static inline void *pg_round_up (const void *va) {
    return (void *) (((uintptr_t) va + PGSIZE - 1) & ~PGMASK);
}

/**
 * External symbol which address is the first address after all data in the BSS segment.
 */
extern int _end_bss;

void test_main(void)
{
    // Get the address of the first unmapped page in the process.
    unsigned page = (unsigned)pg_round_up(&_end_bss);

    // Reserve space for the syscall number and a part of the exit code (1 out of 4 bytes).
    unsigned base = page - sizeof(int) - 1;

    // Call a syscall.
    asm volatile (
        "movl %%esp, %%edi;" // Save the stack pointer in case we survive.
        "movl %0, %%esp;"    // Set stack pointer.
        "movl %1, (%%esp);"  // Try to call SYS_EXIT
        "movb $1, 4(%%esp);" // Set the first byte of the syscall number to zero.
        "int $0x30;"         // Trigger syscall.
        "movl %%edi, %%esp;" // Restore the old stack if we survivied.
        :
        : "r" (base),
          "i" (SYS_EXIT)
        : "%esp", "%eax", "%edi");

    fail("should have died.");
}