ABI và những thứ phá vỡ nó

#ifndef CAUHINH_H
#define CAUHINH_H

typedef struct {
    int rong;
    int cao;
} CauHinh;

void ch_in(const CauHinh *c);

#endif

#include <stdio.h>
#include "cauhinh.h"

int main(void) {
    CauHinh c = { .rong = 1920, .cao = 1080 };

    printf("app  ghi : rong=%d cao=%d  (sizeof=%d)\n",
           c.rong, c.cao, (int)sizeof c);

    ch_in(&c);

    return 0;
}

typedef struct {
    int rong;
    int sau;      /* THEM VAO GIUA */
    int cao;
} CauHinh;

typedef struct { int a; int b; } S;            /* v1, sizeof 8 */
typedef struct { int a; int c; int b; } S;    /* v2: them, doi do doi */
typedef struct { long a; int b; } S;          /* v2: doi kieu, doi kich thuoc */
typedef struct { int b; int a; } S;           /* v2: doi thu tu */

/* Ca bon deu pha ABI. */

int  ham(int x);            /* v1 */
long ham(long x);           /* v2: pha ABI, va tren nhieu he thong
                               con khong pha API vi C tu chuyen kieu,
                               nen loi im lang hoan toan */

void f(int a, int b);       /* v1 */
void f(int b, int a);       /* v2: chi doi TEN tham so -> khong pha gi */
void f(int a, int b, int c);/* v2: them tham so -> pha ABI */

/* v1 co ml_dien_tich, v2 doi thanh ml_tinh_dien_tich */

/* Chuong trinh cu tim ky hieu ml_dien_tich luc chay:
     ./app: symbol lookup error: ./app: undefined symbol: ml_dien_tich

   Day la loi duy nhat trong nhom nay ma he thong BAO RO,
   nen no de sua nhat. */

/* Neu buoc phai doi ten, giu ban cu lam mot lop bao mong: */
double ml_dien_tich(double r) { return ml_tinh_dien_tich(r); }

typedef enum { MAU_DO, MAU_XANH, MAU_VANG } Mau;      /* 0 1 2 */
typedef enum { MAU_DO, MAU_TIM, MAU_XANH, MAU_VANG } Mau;  /* v2 */

/* Chuong trinh cu truyen 1 khi no nghi la MAU_XANH.
   Thu vien moi doc 1 va hieu la MAU_TIM.

   Cach dung: chi bao gio them vao CUOI: */
typedef enum { MAU_DO, MAU_XANH, MAU_VANG, MAU_TIM } Mau;

/* Voi macro thi giong het: */
#define ML_TOI_DA 100        /* v1, dong bang vao ma nguoi dung */
#define ML_TOI_DA 200        /* v2: nguoi dung cu van dung 100 */

/* v1: tra ve 0 khi thanh cong, -1 khi loi */
int ml_luu(const char *tep);

/* v2: tra ve so byte da ghi, hoac so am khi loi */
int ml_luu(const char *tep);

/* Chu ky giong het. Trinh bien dich khong noi gi. Nhung:

     if (ml_luu("a.txt") != 0) bao_loi();      <- gio bao loi khi THANH CONG

   Day la dang pha vo nguy hiem nhat, vi khong cong cu nao bat duoc.
   Neu ban phai doi ngu nghia thi hay DOI TEN HAM. */

gcc -m32 / -m64                /* 32 hay 64 bit */
gcc -fshort-enums              /* enum dung kieu nho nhat du chua */
gcc -fpack-struct              /* bo het phan dem */
gcc -mfloat-abi=hard / softfp  /* tren ARM: truyen so thuc bang thanh ghi nao */
gcc -std=c99 / -std=c11        /* it khi, nhung co the doi kich thuoc kieu */

/* Ban va nguoi dung thu vien PHAI dung cung nhung co nay.
   Do la ly do he thong goi nhu pkg-config ton tai: no luu lai
   dung bo co da dung de dich thu vien. Xem Bai 39.12. */

# 1. abi-compliance-checker: so hai ban thu vien
abi-dumper libmath.so.1.0 -o v1.dump -lver 1.0
abi-dumper libmath.so.1.1 -o v2.dump -lver 1.1
abi-compliance-checker -l libmath -old v1.dump -new v2.dump

# Ket qua la mot bao cao HTML liet ke tung thay doi va muc do:
#   Binary compatibility: 87.5%
#   Removed Symbols: 1
#   Problems with Data Types: High severity: 2

# 2. abidiff, cua bo cong cu libabigail
abidiff libmath.so.1.0 libmath.so.1.1

# Functions changes summary: 0 Removed, 1 Changed, 2 Added
# Variables changes summary: 0 Removed, 0 Changed, 0 Added

# 3. Kiem tra thu cong bang nm, cach nhanh va tho
nm -D --defined-only libmath.so.1.0 | awk '{print $3}' | sort > v1.txt
nm -D --defined-only libmath.so.1.1 | awk '{print $3}' | sort > v2.txt
comm -23 v1.txt v2.txt        # ky hieu BI XOA -> pha ABI
comm -13 v1.txt v2.txt        # ky hieu THEM MOI -> an toan