#include <syscall-nr.h>
#include <stdio.h>
#include <stdint.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;

/**
 * String constants used in the asm blocks.
 */
const char *WORKS = "WORKS\n";
const char *FAIL = "FAIL\n";

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 4 parameters.
    unsigned base = page - sizeof(int) * 4;

    // Call write() with space for 4 parameters (should be fine).
    asm volatile (
        "movl %%esp, %%edi;"
        "movl %0, %%esp;"       // Set stack pointer to right below page boundary.
        "movl %1, (%%esp);"     // Try to call SYS_WRITE
        "movl %2, 4(%%esp);"    // Write to STDOUT
        "movl %3, 8(%%esp);"    // Load buffer.
        "movl $6, 12(%%esp);"   // Write length of string
        "int $0x30;"
        "movl %%edi, %%esp;"    // Restore esp.
        :
        : "r" (base),
          "i" (SYS_WRITE),
          "i" (STDOUT_FILENO),
          "r" (WORKS)
        : "%esp", "%eax", "%edi");


    // Reserve space for 3 parameters (write requires 4).
    base = page - sizeof(int) * 3;

    // Call write() with space for 3 parameters (the kernel should kill us for doing this).
    asm volatile (
        "movl %%esp, %%edi;"
        "movl %0, %%esp;"       // Set stack pointer to right below page boundary.
        "movl %1, (%%esp);"     // Try to call SYS_WRITE
        "movl %2, 4(%%esp);"    // Write to STDOUT
        "movl %3, 8(%%esp);"    // Load buffer.
        //"movl $5, 12(%%esp);" // Can not write the last parameter as we would get a pagefault.
        "int $0x30;"
        "movl %%edi, %%esp;"    // Restore esp in case we do not crash (as we should).
        :
        : "r" (base),
          "i" (SYS_WRITE),
          "i" (STDOUT_FILENO),
          "r" (FAIL)
        : "%esp", "%eax", "%edi");

    fail("should have died.");
}