libc-bottom-half/sources/__environ.c

   1 #include <unistd.h>
   2 #include <stdlib.h>
   3 #include <wasi/api.h>
   4 #include <wasi/libc.h>
   5 #include <wasi/libc-internal.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 // This function is referenced by a weak symbol in crt1.c, and we define
  13 // it here in the same source file as __environ, so that this function is
  14 // linked in iff environment variable support is used.
  15 __wasi_errno_t __wasilibc_populate_environ(void) {
  16     __wasi_errno_t err;
  17
  18     // Get the sizes of the arrays we'll have to create to copy in the environment.
  19     size_t environ_count;
  20     size_t environ_buf_size;
  21     err = __wasi_environ_sizes_get(&environ_count, &environ_buf_size);
  22     if (err != __WASI_ERRNO_SUCCESS) {
  23         return err;
  24     }
  25     if (environ_count == 0) {
  26         return __WASI_ERRNO_SUCCESS;
  27     }
  28
  29     // Add 1 for the NULL pointer to mark the end, and check for overflow.
  30     size_t num_ptrs = environ_count + 1;
  31     if (num_ptrs == 0) {
  32         return __WASI_ERRNO_NOMEM;
  33     }
  34
  35     // Allocate memory for storing the environment chars.
  36     char *environ_buf = malloc(environ_buf_size);
  37     if (environ_buf == NULL) {
  38         return __WASI_ERRNO_NOMEM;
  39     }
  40
  41     // Allocate memory for the array of pointers. This uses `calloc` both to
  42     // handle overflow and to initialize the NULL pointer at the end.
  43     char **environ_ptrs = calloc(num_ptrs, sizeof(char *));
  44     if (environ_ptrs == NULL) {
  45         free(environ_buf);
  46         return __WASI_ERRNO_NOMEM;
  47     }
  48
  49     // Fill the environment chars, and the __environ array with pointers into those chars.
  50     // TODO: Remove the casts on `environ_ptrs` and `environ_buf` once the witx is updated with char8 support.
  51     err = __wasi_environ_get((uint8_t **)environ_ptrs, (uint8_t *)environ_buf);
  52     if (err == __WASI_ERRNO_SUCCESS) {
  53         __environ = environ_ptrs;
  54     } else {
  55         free(environ_buf);
  56         free(environ_ptrs);
  57     }
  58     return err;
  59 }