Đọc bảng ký hiệu

/* kyhieu.c */

int  g_dem = 5;                   /* D: toan cuc, khoi tao khac 0 */
int  g_tong;                      /* B hoac C, xem chu thich duoi */
static int s_rieng = 7;           /* d: static, khoi tao khac 0 */
static int s_khong;               /* b: static, bang 0 */
const char *const TEN = "abc";    /* R: hang cong khai */
static const int BANG[] = {1,2};  /* r: hang static */

void ham_cong_khai(void) { }      /* T */
static void ham_rieng(void) { }   /* t */

extern void ham_o_noi_khac(void); /* U: can tu ngoai */

void f(void) { ham_o_noi_khac(); ham_rieng(); }

nm file.o                    # moi ky hieu
nm -g file.o                 # chi ky hieu TOAN CUC, tuc chu hoa
nm --defined-only file.o     # bo cac ky hieu U
nm -u file.o                 # CHI cac ky hieu U
nm -C file.o                 # giai ma ten C++
nm -S file.o                 # kem KICH THUOC cua tung ky hieu
nm -n file.o                 # sap theo dia chi
nm --size-sort file.o        # sap theo kich thuoc
nm -A *.o                    # kem ten tep o dau moi dong
nm -D lib.so                 # bang ky hieu DONG, cho .so

# Tim ham to nhat trong thu vien, huu ich khi giam kich thuoc

$ nm --size-sort -S --radix=d libmath.a | tail -5
0000000000000112 T uoc_chung_lon_nhat
0000000000000156 T giai_thua
0000000000000284 T dt_hinh_tron

# --radix=d in kich thuoc he muoi thay vi he muoi sau

# Va tren ban thuc thi, tim phan doan nao chiem cho:
$ size app
   text	   data	    bss	    dec	    hex	filename
   9241	    644	     24	   9909	   26b5	app

# Linux
ldd app                        # danh sach va DUONG DAN THAT SU duoc nap
objdump -p app | grep NEEDED   # danh sach ghi trong tep, khong giai duong dan
readelf -d app                 # ca phan doan dong

$ ldd app
	linux-vdso.so.1 (0x00007ffd8f3f1000)
	libmath.so => /home/a/duan/build/libmath.so (0x00007f2b1c000000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f2b1bc00000)
	/lib64/ld-linux-x86-64.so.2 (0x00007f2b1c200000)

# macOS
otool -L app

# Windows
objdump -p app.exe | grep 'DLL Name'
dumpbin /dependents app.exe     # neu co Visual Studio

# Trieu chung:
#   undefined reference to 'sv_them'

# Buoc 1: ky hieu do co ton tai o dau khong?
nm -A build/*.o build/*.a 2>/dev/null | grep sv_them

#   Neu KHONG ra gi     -> ban chua dich tep chua ham do
#   Neu ra " U sv_them" -> chi co noi CAN, khong co noi DINH NGHIA
#   Neu ra " t sv_them" -> ham do la static, do la nguyen nhan
#   Neu ra " T sv_them" -> co day du, van de la THU TU lien ket

# Buoc 2: neu co T, kiem tra thu tu
gcc main.c -Lbuild -lsv -o app        # thu vien SAU main.c

# Buoc 3: xem trinh lien ket mo nhung tep nao
gcc main.c -Lbuild -lsv -Wl,-t -o app

# Buoc 4: theo dau mot ky hieu cu the
gcc main.c -Lbuild -lsv -Wl,--trace-symbol=sv_them -o app

# Bo lenh kiem tra mot thu vien truoc khi phat hanh

echo "=== ky hieu xuat ra ==="
nm -D --defined-only libmath.so | grep -E ' [TDBR] ' | wc -l

echo "=== ky hieu can tu ngoai ==="
nm -D -u libmath.so | wc -l

echo "=== phu thuoc ==="
objdump -p libmath.so | grep NEEDED

echo "=== kich thuoc tung phan doan ==="
size -A libmath.so | head -8

echo "=== co con thong tin go loi khong ==="
readelf -S libmath.so | grep debug | wc -l

echo "=== SONAME ==="
objdump -p libmath.so | grep SONAME