Struct array member
8981 단어 struct
#include <stdio.h>
// This struct does not store jp_data:
// +-+-+-+-+
// 0+-+-+-+-+ jp_len
// 3 2 1 0
struct zero_size_array_struct {
int jp_len;
char jp_data[0];
};
// This struct stores a char pointer:
// +-+-+-+-+
// 1+-+-+-+-+ jp_data
// 0+-+-+-+-+ jp_len
// 3 2 1 0
struct pointer_struct {
int jp_len;
char* jp_data;
};
// This struct stores a 8-char array:
// +-+-+-+-+
// 2+-+-+-+-+
// 1+-+-+-+-+ jp_data
// 0+-+-+-+-+ jp_len
// 3 2 1 0
struct array_struct {
int jp_len;
char jp_data[8];
};
char data[] = {0, 1, 2, 3, 4, 5, 6, 7};
struct zero_size_array_struct* one = (struct zero_size_array_struct*) data;
struct pointer_struct* two = (struct pointer_struct*) data;
struct array_struct* three = (struct array_struct*) data;
struct array_struct instance = { 0x100, {0x10, 0x20, 0x30, 0x40, 0x50, 0x60, 0x70, 0x80} };
struct array_struct* four = &instance;
void sizes() {
printf("sizeof(struct zero_size_array_struct): %d
", sizeof(struct zero_size_array_struct));
printf("sizeof(struct pointer_struct): %d
", sizeof(struct pointer_struct));
printf("sizeof(struct array_struct): %d
", sizeof(struct array_struct));
}
int main(int argc, const char *argv[]) {
printf("~~~~~~~~~~~~~~~~~~~~~~~~~~
");
printf("struct pointer: %08x
", one);
printf("jp_len: %08x
", one->jp_len);
// movl one, %eax
// leal 4(%eax), %edx
printf("jp_data: %08x
", one->jp_data);
printf("jp_data[0]: %08x
", one->jp_data[0]);
printf("jp_data[1]: %08x
", one->jp_data[1]);
printf("jp_data[1]: %08x
", *((char *) one + 5));
printf("~~~~~~~~~~~~~~~~~~~~~~~~~~
");
printf("struct pointer: %08x
", two);
printf("jp_len: %08x
", two->jp_len);
// movl two, %eax
// movl 4(%eax), %edx
printf("jp_data: %08x
", two->jp_data);
printf("~~~~~~~~~~~~~~~~~~~~~~~~~~
");
printf("struct pointer: %08x
", three);
printf("jp_len: %08x
", three->jp_len);
// movl three, %eax
// leal 4(%eax), %edx
printf("jp_data: %08x
", three->jp_data);
printf("jp_data[0]: %08x
", three->jp_data[0]);
printf("jp_data[1]: %08x
", three->jp_data[1]);
printf("jp_data[1]: %08x
", *((char *) three + 5));
printf("~~~~~~~~~~~~~~~~~~~~~~~~~~
");
printf("struct pointer: %08x
", four);
printf("jp_len: %08x
", four->jp_len);
// movl four, %eax
// leal 4(%eax), %edx
printf("jp_data: %08x
", four->jp_data);
printf("jp_data[0]: %08x
", four->jp_data[0]);
printf("jp_data[1]: %08x
", four->jp_data[1]);
printf("jp_data[1]: %08x
", *((char *) four + 5));
return 0;
}
Assembly code:
.file "fix.c"
.globl data
.data
.type data, @object
.size data, 8
data:
.byte 0
.byte 1
.byte 2
.byte 3
.byte 4
.byte 5
.byte 6
.byte 7
.globl one
.align 4
.type one, @object
.size one, 4
one:
.long data
.globl two
.align 4
.type two, @object
.size two, 4
two:
.long data
.globl three
.align 4
.type three, @object
.size three, 4
three:
.long data
.globl instance
.align 4
.type instance, @object
.size instance, 12
instance:
.long 256
.byte 16
.byte 32
.byte 48
.byte 64
.byte 80
.byte 96
.byte 112
.byte -128
.globl four
.align 4
.type four, @object
.size four, 4
four:
.long instance
.section .rodata
.align 4
.LC0:
.string "sizeof(struct zero_size_array_struct): %d
"
.align 4
.LC1:
.string "sizeof(struct pointer_struct): %d
"
.align 4
.LC2:
.string "sizeof(struct array_struct): %d
"
.text
.globl sizes
.type sizes, @function
sizes:
pushl %ebp
movl %esp, %ebp
subl $24, %esp
movl $.LC0, %eax
movl $4, 4(%esp)
movl %eax, (%esp)
call printf
movl $.LC1, %eax
movl $8, 4(%esp)
movl %eax, (%esp)
call printf
movl $.LC2, %eax
movl $12, 4(%esp)
movl %eax, (%esp)
call printf
leave
ret
.size sizes, .-sizes
.section .rodata
.LC3:
.string "~~~~~~~~~~~~~~~~~~~~~~~~~~"
.LC4:
.string "struct pointer: %08x
"
.LC5:
.string "jp_len: %08x
"
.LC6:
.string "jp_data: %08x
"
.LC7:
.string "jp_data[0]: %08x
"
.LC8:
.string "jp_data[1]: %08x
"
.text
.globl main
.type main, @function
main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $16, %esp
movl $.LC3, (%esp)
call puts
movl one, %edx
movl $.LC4, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl one, %eax
movl (%eax), %edx
movl $.LC5, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl one, %eax
leal 4(%eax), %edx
movl $.LC6, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl one, %eax
movzbl 4(%eax), %eax
movsbl %al,%edx
movl $.LC7, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl one, %eax
movzbl 5(%eax), %eax
movsbl %al,%edx
movl $.LC8, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl one, %eax
addl $5, %eax
movzbl (%eax), %eax
movsbl %al,%edx
movl $.LC8, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl $.LC3, (%esp)
call puts
movl two, %edx
movl $.LC4, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl two, %eax
movl (%eax), %edx
movl $.LC5, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl two, %eax
movl 4(%eax), %edx
movl $.LC6, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl $.LC3, (%esp)
call puts
movl three, %edx
movl $.LC4, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl three, %eax
movl (%eax), %edx
movl $.LC5, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl three, %eax
leal 4(%eax), %edx
movl $.LC6, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl three, %eax
movzbl 4(%eax), %eax
movsbl %al,%edx
movl $.LC7, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl three, %eax
movzbl 5(%eax), %eax
movsbl %al,%edx
movl $.LC8, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl three, %eax
addl $5, %eax
movzbl (%eax), %eax
movsbl %al,%edx
movl $.LC8, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl $.LC3, (%esp)
call puts
movl four, %edx
movl $.LC4, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl four, %eax
movl (%eax), %edx
movl $.LC5, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl four, %eax
leal 4(%eax), %edx
movl $.LC6, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl four, %eax
movzbl 4(%eax), %eax
movsbl %al,%edx
movl $.LC7, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl four, %eax
movzbl 5(%eax), %eax
movsbl %al,%edx
movl $.LC8, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl four, %eax
addl $5, %eax
movzbl (%eax), %eax
movsbl %al,%edx
movl $.LC8, %eax
movl %edx, 4(%esp)
movl %eax, (%esp)
call printf
movl $0, %eax
leave
ret
.size main, .-main
.ident "GCC: (Ubuntu 4.4.3-4ubuntu5.1) 4.4.3"
.section .note.GNU-stack,"",@progbits
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