Valgrind và bốn loại rò rỉ

# Bo co day du, nen thuoc long
valgrind --leak-check=full \
         --show-leak-kinds=all \
         --track-origins=yes \
         --error-exitcode=1 \
         ./prog

# Giai thich tung co:
#   --leak-check=full        liet ke tung cho ro ri, khong chi tong so
#   --show-leak-kinds=all    hien ca bon loai, khong chi "definitely"
#   --track-origins=yes      voi bien chua khoi tao: chi ra NOI SINH RA no.
#                            Cham hon nhung gan nhu luon dang gia
#   --error-exitcode=1       tra ve 1 khi co loi, de CI phat hien duoc

typedef struct Nut {
    int         gia_tri;
    struct Nut *sau;
} Nut;

static char *g_bo_dem;              /* bien toan cuc */

int main(void) {
    /* 1. definitely lost: mat con tro */
    char *a = malloc(10);
    a = malloc(20);                 /* khoi 10 byte khong ai giu nua */

    /* 2. indirectly lost: danh sach mat ca chuoi */
    Nut *dau = malloc(sizeof *dau);
    dau->sau = malloc(sizeof *dau); /* nut thu hai */
    dau->sau->sau = NULL;
    dau = NULL;                     /* nut 1 definitely, nut 2 indirectly */

    /* 3. possibly lost: con tro tro vao giua khoi */
    char *b = malloc(100);
    b += 50;                        /* khong con tro vao dau khoi */

    /* 4. still reachable: van co con tro toan cuc tro toi */
    g_bo_dem = malloc(30);

    free(a);
    return 0;
}

#include <stdio.h>
#include <stdlib.h>

static int tinh(int *a, int n) {
    int t;                       /* quen khoi tao */

    for (int i = 0; i < n; ++i) t += a[i];

    return t;
}

int main(void) {
    int a[3] = { 1, 2, 3 };

    printf("tong = %d\n", tinh(a, 3));

    return 0;
}

==12345== Invalid write of size 4
==12345==    at 0x4005A1: main (tbd.c:8)              <- DONG GHI SAI
==12345==  Address 0x5204054 is 0 bytes after a block of size 20 alloc'd
==12345==    at 0x4C2FB0F: malloc (vg_replace_malloc.c:299)
==12345==    by 0x400591: main (tbd.c:5)              <- DONG CAP PHAT

/* Doc tu tren xuong:
     1. Loai loi va kich thuoc: ghi 4 byte
     2. Vet goi toi cho ghi, dong tren cung la dong cua ban
     3. Vi tri tuong doi: "0 bytes after a block of size 20"
     4. Vet goi toi cho cap phat

   Cau truc giong het bao cao cua ASan o Bai 34.2. Hai cong cu
   khac nhau ve co che nhung giong nhau ve nhung gi ban can biet. */

# Memcheck: mac dinh, phat hien loi bo nho
valgrind ./prog
valgrind --tool=memcheck ./prog

# Callgrind: dem so lenh moi ham, de tim diem nong
valgrind --tool=callgrind ./prog
callgrind_annotate callgrind.out.12345 | head -30
kcachegrind callgrind.out.12345          # giao dien do hoa

# Massif: theo doi bo nho heap theo thoi gian
valgrind --tool=massif ./prog
ms_print massif.out.12345

# Helgrind: phat hien dua du lieu va khoa cheo
valgrind --tool=helgrind ./prog

# DRD: cung muc dich voi Helgrind, thuat toan khac
valgrind --tool=drd ./prog

# Cachegrind: mo phong bo nho dem CPU
valgrind --tool=cachegrind ./prog