fusl/src/env/__libc_start_main.c

#include <elf.h>
#include <poll.h>
#include <fcntl.h>
#include <signal.h>
#include "syscall.h"
#include "atomic.h"
#include "libc.h"

void __init_tls(size_t*);

static void dummy(void) {}
weak_alias(dummy, _init);

__attribute__((__weak__, __visibility__("hidden"))) extern void (
    *const __init_array_start)(void),
    (*const __init_array_end)(void);

static void dummy1(void* p) {}
weak_alias(dummy1, __init_ssp);

#define AUX_CNT 38

void __init_libc(char** envp, char* pn) {
  size_t i, *auxv, aux[AUX_CNT] = {0};
  __environ = envp;
  for (i = 0; envp[i]; i++)
    ;
  libc.auxv = auxv = (void*)(envp + i + 1);
  for (i = 0; auxv[i]; i += 2)
    if (auxv[i] < AUX_CNT)
      aux[auxv[i]] = auxv[i + 1];
  __hwcap = aux[AT_HWCAP];
  __sysinfo = aux[AT_SYSINFO];
  libc.page_size = aux[AT_PAGESZ];

  if (pn) {
    __progname = __progname_full = pn;
    for (i = 0; pn[i]; i++)
      if (pn[i] == '/')
        __progname = pn + i + 1;
  }

  __init_tls(aux);
  __init_ssp((void*)aux[AT_RANDOM]);

  if (aux[AT_UID] == aux[AT_EUID] && aux[AT_GID] == aux[AT_EGID] &&
      !aux[AT_SECURE])
    return;

  struct pollfd pfd[3] = {{.fd = 0}, {.fd = 1}, {.fd = 2}};
#ifdef SYS_poll
  __syscall(SYS_poll, pfd, 3, 0);
#else
  __syscall(SYS_ppoll, pfd, 3, &(struct timespec){0}, 0, _NSIG / 8);
#endif
  for (i = 0; i < 3; i++)
    if (pfd[i].revents & POLLNVAL)
      if (__sys_open("/dev/null", O_RDWR) < 0)
        a_crash();
  libc.secure = 1;
}

static void libc_start_init(void) {
  _init();
  uintptr_t a = (uintptr_t)&__init_array_start;
  for (; a < (uintptr_t)&__init_array_end; a += sizeof(void (*)()))
    (*(void (**)())a)();
}

weak_alias(libc_start_init, __libc_start_init);

int __libc_start_main(int (*main)(int, char**, char**), int argc, char** argv) {
  char** envp = argv + argc + 1;

  __init_libc(envp, argv[0]);
  __libc_start_init();

  /* Pass control to the application */
  exit(main(argc, argv, envp));
  return 0;
}