Styjun

I'm reading a book on coding an operating system and I'm writing the C code examples they have in the book and compiling and testing the code in the terminal but I ran into a problem with this code.

The file with this code in it is named "hello.c".
I compiled the file with "gcc hello.c -o hello"
and then ran it with "./hello".

I received the message Segmentation fault (core dumped),
and I'm unsure of what I'm doing wrong.

#include <stdio.h>

void preinit1() 
 printf("%sn", __FUNCTION__);


void preinit2() 
 printf("%sn", __FUNCTION__);


void init1() 
 printf("%sn", __FUNCTION__);


void init2() 
 printf("%sn", __FUNCTION__);


typedef void (*preinit)();
typedef void (*init)();

__attribute__((section(".init_array"))) preinit
 preinit_arr[2] = preinit1, preinit2;

__attribute__((section(".init_array"))) init
 init_arr[2] = init1, init2;

int main(int argc, char *argv[])

 printf("hello world!n");

 return 0;

I don't think you're supposed to add arrays to the section (you've an error in the example, initializing the .init_array twice).

__attribute__((section(".preinit_array"))) preinit preinit_arr1 = preinit1;
__attribute__((section(".preinit_array"))) preinit preinit_arr2 = preinit2;

__attribute__((section(".init_array"))) init init_arr1 = init1;
__attribute__((section(".init_array"))) init init_arr2 = init2;

This is the section declared using arrays

objdump -s -j .init_array hello.orig 

hello.orig: file format elf64-x86-64

Contents of section .init_array:
 3dc0 30110000 00000000 00000000 00000000 0...............
 3dd0 35110000 00000000 48110000 00000000 5.......H.......
 3de0 5b110000 00000000 6e110000 00000000 [.......n.......

This is the section that works

objdump -s -j .init_array hello

hello: file format elf64-x86-64

Contents of section .init_array:
 3dc8 30110000 00000000 35110000 00000000 0.......5.......
 3dd8 48110000 00000000 5b110000 00000000 H.......[.......
 3de8 6e110000 00000000 n.......

In the former there's the null pointer at 3dc8 that probably cause the segmentation (see below), I have no idea why is there maybe somebody other can explain.

(gdb) bt
#0 0x0000000000000000 in ?? ()
#1 0x00005555555551f5 in __libc_csu_init ()
#2 0x00007ffff7dec02a in __libc_start_main (main=0x555555555181 <main>, argc=1, argv=0x7fffffffe1f8, init=0x5555555551b0 <__libc_csu_init>, 
 fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7fffffffe1e8) at ../csu/libc-start.c:264
#3 0x000055555555507a in _start ()

Fixing only the typo about .preinit_array make the preinit calls work but not the init