/*

$ ./a.out 
DYNAMIC=0x601100
DEBUG=0x7f7e00e10780
r_version = 0
l_addr = 0x0, l_name = './a.out', l_ld = 0x601100
l_addr = 0x753ead400000, l_name = '/usr/lib/libc.so.12', l_ld = 0x753ead7d0780
l_addr = 0x7f7e00c00000, l_name = '/usr/libexec/ld.elf_so', l_ld = 0x7f7e00e0ff00
r_brk = 0x7f7e00c00cd0
r_state = CONSISTENT
*/

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

#include <dlfcn.h>
#include <elf.h>
#include <link.h>

#include <err.h>

void *
get_dynamic(void)
{
	AuxInfo *aux = _dlauxinfo();
	uintptr_t relocbase = (uintptr_t)~0U;
	const Elf_Phdr *phdr = NULL;
	Elf_Half phnum = (Elf_Half)~0;

	for (; aux->a_type != AT_NULL; ++aux) {
		switch (aux->a_type) {
		case AT_PHDR:
			phdr = (void *)aux->a_v;
			break;
		case AT_PHNUM:
			phnum = (Elf_Half)aux->a_v;
			break;
		}
	}

	if (phdr == NULL)
		errx(EXIT_FAILURE, "phdr == NULL");
	if (phnum == (Elf_Half)~0)
		errx(EXIT_FAILURE, "phnum == (Elf_Half)~0");

	const Elf_Phdr *phlimit = phdr + phnum, *dynphdr = NULL;

	for (; phdr < phlimit; ++phdr) {
		if (phdr->p_type == PT_DYNAMIC)
			dynphdr = phdr;
		if (phdr->p_type == PT_PHDR)
			relocbase = (uintptr_t)phdr - phdr->p_vaddr;
	}
	if (dynphdr == NULL)
		errx(EXIT_FAILURE, "dynphdr == NULL");
	if (relocbase == (uintptr_t)~0U)
		errx(EXIT_FAILURE, "relocbase == (uintptr_t)~0U");

	Elf_Dyn *dynp = (Elf_Dyn *)((uint8_t *)dynphdr->p_vaddr + relocbase);

	return dynp;
}

struct r_debug *
get_r_debug()
{
	Elf_Dyn *dynp = get_dynamic();

	printf("DYNAMIC=%p\n", dynp);

	for (; dynp->d_tag != DT_NULL; dynp++) {
		if (dynp->d_tag == DT_DEBUG)
			return (void *)dynp->d_un.d_val;
	}

	errx(EXIT_FAILURE, "DT_DEBUG not found");
}

int
main(int argc, char **argv)
{
	struct r_debug *r_debug;

	r_debug = get_r_debug();

	printf("DEBUG=%p\n", r_debug);

	printf("r_version = %d\n", r_debug->r_version);

	struct link_map *map;

	for (map = r_debug->r_map; map; map = map->l_next) {
		printf("l_addr = %p, l_name = '%s', l_ld = %p\n",
		    map->l_addr, map->l_name, map->l_ld);
	}

	printf("r_brk = %p\n", r_debug->r_brk);

	const char *r_state;
	switch (r_debug->r_state) {
	case RT_CONSISTENT:
		r_state = "CONSISTENT";
		break;
	case RT_ADD:
		r_state = "ADD";
		break;
	case RT_DELETE:
		r_state = "DELETE";
		break;
	default:
		r_state = "???";
	}
	printf("r_state = %s\n", r_state);

	return EXIT_SUCCESS;
}