libc-bottom-half/sources/__wasilibc_initialize_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 #include <wasi/libc-environ.h>
   7
   8 /// If the program doesn't use `environ`, it'll get this version of
   9 /// `__wasilibc_environ`, which isn't initialized with a constructor function.
  10 /// `getenv` etc. call `__wasilibc_ensure_environ()` before accessing it.
  11 /// Statically-initialize it to an invalid pointer value so that we can
  12 /// detect if it's been explicitly initialized (we can't use `NULL` because
  13 /// `clearenv` sets it to NULL.
  14 char **__wasilibc_environ weak = (char **)-1;
  15
  16 // See the comments in libc-environ.h.
  17 void __wasilibc_ensure_environ(void) {
  18     if (__wasilibc_environ == (char **)-1) {
  19         __wasilibc_initialize_environ();
  20     }
  21 }
  22
  23 /// Avoid dynamic allocation for the case where there are no environment
  24 /// variables, but we still need a non-NULL pointer to an (empty) array.
  25 static char *empty_environ[1] = { NULL };
  26
  27 // See the comments in libc-environ.h.
  28 void __wasilibc_initialize_environ(void) {
  29     // Get the sizes of the arrays we'll have to create to copy in the environment.
  30     size_t environ_count;
  31     size_t environ_buf_size;
  32     __wasi_errno_t err = __wasi_environ_sizes_get(&environ_count, &environ_buf_size);
  33     if (err != __WASI_ERRNO_SUCCESS) {
  34         goto oserr;
  35     }
  36     if (environ_count == 0) {
  37         __wasilibc_environ = empty_environ;
  38         return;
  39     }
  40
  41     // Add 1 for the NULL pointer to mark the end, and check for overflow.
  42     size_t num_ptrs = environ_count + 1;
  43     if (num_ptrs == 0) {
  44         goto software;
  45     }
  46
  47     // Allocate memory for storing the environment chars.
  48     char *environ_buf = malloc(environ_buf_size);
  49     if (environ_buf == NULL) {
  50         goto software;
  51     }
  52
  53     // Allocate memory for the array of pointers. This uses `calloc` both to
  54     // handle overflow and to initialize the NULL pointer at the end.
  55     char **environ_ptrs = calloc(num_ptrs, sizeof(char *));
  56     if (environ_ptrs == NULL) {
  57         free(environ_buf);
  58         goto software;
  59     }
  60
  61     // Fill the environment chars, and the `__wasilibc_environ` array with
  62     // pointers into those chars.
  63     // TODO: Remove the casts on `environ_ptrs` and `environ_buf` once the witx is updated with char8 support.
  64     err = __wasi_environ_get((uint8_t **)environ_ptrs, (uint8_t *)environ_buf);
  65     if (err != __WASI_ERRNO_SUCCESS) {
  66         free(environ_buf);
  67         free(environ_ptrs);
  68         goto oserr;
  69     }
  70
  71     __wasilibc_environ = environ_ptrs;
  72     return;
  73 oserr:
  74     _Exit(EX_OSERR);
  75 software:
  76     _Exit(EX_SOFTWARE);
  77 }
  78
  79 // See the comments in libc-environ.h.
  80 void __wasilibc_deinitialize_environ(void) {
  81     if (__wasilibc_environ != (char **)-1) {
  82         // Let libc-top-half clear the old environment-variable strings.
  83         clearenv();
  84         // Set the pointer to the special init value.
  85         __wasilibc_environ = (char **)-1;
  86     }
  87 }
  88
  89 // See the comments in libc-environ.h.
  90 weak
  91 void __wasilibc_maybe_reinitialize_environ_eagerly(void) {
  92     // This version does nothing. It may be overridden by a version which does
  93     // something if `environ` is used.
  94 }