Question

Consider the following source code, where b, c, and d are constants declared with #define. You will need to determine the values for b, c, and d.

struct lnode {
char *str;
struct lnode *next;
}
struct lnode A[b][c][d];
int store_ele(int h, int i, int j, struct lnode dest) {
A[h][i][j] = dest;
return sizeof(A);}
On compiling this program (with -O2), GCC generates the following assembly code for the store_ele function:
store_ele:
movslq %edi, %rdi
movslq %esi, %rsi
movslq %edx, %rax
imulq $0x134, %rdi, %rdi
leaq 0x0(,%rsi,8), %rdx
subq %rsi, %rdx
leaq (%rdi,%rdx,4), %rdx
addq %rax, %rdx
salq $0x4, %rdx
movq %rcx, A(%rdx)
movq %r8, A+0x8(%rdx)
movl $0x33bc0, %eax
ret

How would i solve this problem? I am pretty sure that the size of array is 13244 and the size of the struct is 16. I am to solve for b,c,and d

Answer 1

There are many possible combination but according to me this should be the b c and d, and 13244 shoud be 13248 because size should be in multiple of 4.

b= 3 c= 12 d= 23

3*12*23 = 828 * 16 = 13248

#define b 3

#define c 12

#define d 23

struct lnode {
char *str;
struct lnode *next;
}
struct lnode A[b][c][d];
int store_ele(int h, int i, int j, struct lnode dest) {
A[h][i][j] = dest;
return sizeof(A);}

assembly:

store_ele:
.LFB0:
.cfi_startproc
movslq %esi, %rsi
movslq %edi, %rdi
movslq %edx, %rax
imulq $276, %rdi, %rdi
leaq (%rsi,%rsi,2), %rdx
salq $3, %rdx
subq %rsi, %rdx
addq %rdi, %rdx
addq %rax, %rdx
leaq A(%rip), %rax
salq $4, %rdx
addq %rax, %rdx
movl $13248, %eax
movq %rcx, (%rdx)
movq %r8, 8(%rdx)
ret