libc-bottom-half/sources/__environ.c

   1 #include <unistd.h>
   2 #include <stdlib.h>
   3 #include <sysexits.h>
   4 #include <wasi/api.h>
   5 #include <wasi/libc.h>
   6
   7 static char *empty_environ[1] = { NULL };
   8 char **__environ = empty_environ;
   9 extern __typeof(__environ) _environ __attribute__((weak, alias("__environ")));
  10 extern __typeof(__environ) environ __attribute__((weak, alias("__environ")));
  11
  12 // We define this function here in the same source file as __environ, so that
  13 // this function is called in iff environment variable support is used.
  14 // Concerning the 50 -- levels up to 100 are reserved for the implementation,
  15 // so we an arbitrary number in the middle of the range to allow other
  16 // reserved things to go before or after.
  17 __attribute__((constructor(50)))
  18 static void __wasilibc_populate_environ(void) {
  19     __wasi_errno_t err;
  20
  21     // Get the sizes of the arrays we'll have to create to copy in the environment.
  22     size_t environ_count;
  23     size_t environ_buf_size;
  24     err = __wasi_environ_sizes_get(&environ_count, &environ_buf_size);
  25     if (err != __WASI_ERRNO_SUCCESS) {
  26         goto oserr;
  27     }
  28     if (environ_count == 0) {
  29         return;
  30     }
  31
  32     // Add 1 for the NULL pointer to mark the end, and check for overflow.
  33     size_t num_ptrs = environ_count + 1;
  34     if (num_ptrs == 0) {
  35         goto software;
  36     }
  37
  38     // Allocate memory for storing the environment chars.
  39     char *environ_buf = malloc(environ_buf_size);
  40     if (environ_buf == NULL) {
  41         goto software;
  42     }
  43
  44     // Allocate memory for the array of pointers. This uses `calloc` both to
  45     // handle overflow and to initialize the NULL pointer at the end.
  46     char **environ_ptrs = calloc(num_ptrs, sizeof(char *));
  47     if (environ_ptrs == NULL) {
  48         free(environ_buf);
  49         goto software;
  50     }
  51
  52     // Fill the environment chars, and the __environ array with pointers into those chars.
  53     // TODO: Remove the casts on `environ_ptrs` and `environ_buf` once the witx is updated with char8 support.
  54     err = __wasi_environ_get((uint8_t **)environ_ptrs, (uint8_t *)environ_buf);
  55     if (err != __WASI_ERRNO_SUCCESS) {
  56         free(environ_buf);
  57         free(environ_ptrs);
  58         goto oserr;
  59     }
  60
  61     __environ = environ_ptrs;
  62     return;
  63 oserr:
  64     _Exit(EX_OSERR);
  65 software:
  66     _Exit(EX_SOFTWARE);
  67 }