__libc_start_main.c raw

   1  #include <elf.h>
   2  #include <poll.h>
   3  #include <fcntl.h>
   4  #include <signal.h>
   5  #include <unistd.h>
   6  #include "syscall.h"
   7  #include "atomic.h"
   8  #include "libc.h"
   9  
  10  static void dummy(void) {}
  11  weak_alias(dummy, _init);
  12  
  13  extern weak hidden void (*const __init_array_start)(void), (*const __init_array_end)(void);
  14  
  15  static void dummy1(void *p) {}
  16  weak_alias(dummy1, __init_ssp);
  17  
  18  #define AUX_CNT 38
  19  
  20  #ifdef __GNUC__
  21  __attribute__((__noinline__))
  22  #endif
  23  void __init_libc(char **envp, char *pn)
  24  {
  25  	size_t i, *auxv, aux[AUX_CNT] = { 0 };
  26  	__environ = envp;
  27  	for (i=0; envp[i]; i++);
  28  	libc.auxv = auxv = (void *)(envp+i+1);
  29  	for (i=0; auxv[i]; i+=2) if (auxv[i]<AUX_CNT) aux[auxv[i]] = auxv[i+1];
  30  	__hwcap = aux[AT_HWCAP];
  31  	if (aux[AT_SYSINFO]) __sysinfo = aux[AT_SYSINFO];
  32  	libc.page_size = aux[AT_PAGESZ];
  33  
  34  	if (!pn) pn = (void*)aux[AT_EXECFN];
  35  	if (!pn) pn = "";
  36  	__progname = __progname_full = pn;
  37  	for (i=0; pn[i]; i++) if (pn[i]=='/') __progname = pn+i+1;
  38  
  39  	__init_tls(aux);
  40  	__init_ssp((void *)aux[AT_RANDOM]);
  41  
  42  	if (aux[AT_UID]==aux[AT_EUID] && aux[AT_GID]==aux[AT_EGID]
  43  		&& !aux[AT_SECURE]) return;
  44  
  45  	struct pollfd pfd[3] = { {.fd=0}, {.fd=1}, {.fd=2} };
  46  	int r =
  47  #ifdef SYS_poll
  48  	__syscall(SYS_poll, pfd, 3, 0);
  49  #else
  50  	__syscall(SYS_ppoll, pfd, 3, &(struct timespec){0}, 0, _NSIG/8);
  51  #endif
  52  	if (r<0) a_crash();
  53  	for (i=0; i<3; i++) if (pfd[i].revents&POLLNVAL)
  54  		if (__sys_open("/dev/null", O_RDWR)<0)
  55  			a_crash();
  56  	libc.secure = 1;
  57  }
  58  
  59  static void libc_start_init(void)
  60  {
  61  	_init();
  62  	uintptr_t a = (uintptr_t)&__init_array_start;
  63  	for (; a<(uintptr_t)&__init_array_end; a+=sizeof(void(*)()))
  64  		(*(void (**)(void))a)();
  65  }
  66  
  67  weak_alias(libc_start_init, __libc_start_init);
  68  
  69  typedef int lsm2_fn(int (*)(int,char **,char **), int, char **);
  70  static lsm2_fn libc_start_main_stage2;
  71  
  72  int __libc_start_main(int (*main)(int,char **,char **), int argc, char **argv,
  73  	void (*init_dummy)(), void(*fini_dummy)(), void(*ldso_dummy)())
  74  {
  75  	char **envp = argv+argc+1;
  76  
  77  	/* External linkage, and explicit noinline attribute if available,
  78  	 * are used to prevent the stack frame used during init from
  79  	 * persisting for the entire process lifetime. */
  80  	__init_libc(envp, argv[0]);
  81  
  82  	/* Barrier against hoisting application code or anything using ssp
  83  	 * or thread pointer prior to its initialization above. */
  84  	lsm2_fn *stage2 = libc_start_main_stage2;
  85  	__asm__ ( "" : "+r"(stage2) : : "memory" );
  86  	return stage2(main, argc, argv);
  87  }
  88  
  89  static int libc_start_main_stage2(int (*main)(int,char **,char **), int argc, char **argv)
  90  {
  91  	char **envp = argv+argc+1;
  92  	__libc_start_init();
  93  
  94  	/* Pass control to the application */
  95  	exit(main(argc, argv, envp));
  96  	return 0;
  97  }
  98