libc-top-half/musl/src/env/__libc_start_main.c

   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 {
  74         char **envp = argv+argc+1;
  75
  76         /* External linkage, and explicit noinline attribute if available,
  77          * are used to prevent the stack frame used during init from
  78          * persisting for the entire process lifetime. */
  79         __init_libc(envp, argv[0]);
  80
  81         /* Barrier against hoisting application code or anything using ssp
  82          * or thread pointer prior to its initialization above. */
  83         lsm2_fn *stage2 = libc_start_main_stage2;
  84         __asm__ ( "" : "+r"(stage2) : : "memory" );
  85         return stage2(main, argc, argv);
  86 }
  87
  88 static int libc_start_main_stage2(int (*main)(int,char **,char **), int argc, char **argv)
  89 {
  90         char **envp = argv+argc+1;
  91         __libc_start_init();
  92
  93         /* Pass control to the application */
  94         exit(main(argc, argv, envp));
  95         return 0;
  96 }