initfini.c

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#include <stddef.h>
#include <stdlib.h>
#include <stdio.h>

extern void (*__preinit_array_start []) (void) __attribute__((weak));
extern void (*__preinit_array_end []) (void) __attribute__((weak));
extern void (*__init_array_start []) (void) __attribute__((weak));
extern void (*__init_array_end []) (void) __attribute__((weak));
extern void (*__fini_array_start []) (void) __attribute__((weak));
extern void (*__fini_array_end []) (void) __attribute__((weak));

void _init();
void _fini();
void _exit(int return_code) __attribute__((noreturn));


static void __libc_init_array() {
    size_t count, i;
    
    count = __preinit_array_end - __preinit_array_start;
    for (i = 0; i < count; i++)
        __preinit_array_start[i]();
    
    _init();

    count = __init_array_end - __init_array_start;
    for (i = 0; i < count; i++)
        __init_array_start[i]();
}

static void __libc_fini_array() {
    size_t count, i;
    
    count = __preinit_array_end - __preinit_array_start;
    for (i = count - 1; i >= 0; i--)
        __fini_array_start[i]();
    
    _fini();
}

#define MAX_ATEXIT 32

static volatile uint8_t atexit_count = 0;
static volatile atexit_func_t atexit_funcs[MAX_ATEXIT];

int atexit(atexit_func_t func) {
    uint8_t pos = __sync_fetch_and_add(&atexit_count, 1);
    
    if (pos >= MAX_ATEXIT) {
        atexit_count = 32;
        return -1;
    }
    
    atexit_funcs[pos] = func;
    return 0;
}

void exit(int return_code) {
    uint8_t i;
    
    for (i = 0; i < atexit_count; i++) {
        atexit_funcs[i]();
    }
    
    __libc_fini_array();
    _exit(return_code);
}

void libc_init() {
    __sinit(_impure_ptr);
    __libc_init_array();
}