1 files changed, 93 insertions, 0 deletions
diff --git a/libc-bottom-half/sources/__wasilibc_initialize_environ.c b/libc-bottom-half/sources/__wasilibc_initialize_environ.c
new file mode 100644
index 0000000..2d31c5d
--- /dev/null
+++ b/libc-bottom-half/sources/__wasilibc_initialize_environ.c
@@ -0,0 +1,93 @@
+#include <unistd.h>
+#include <stdlib.h>
+#include <sysexits.h>
+#include <wasi/api.h>
+#include <wasi/libc.h>
+#include <wasi/libc-environ.h>
+
+/// If the program doesn't use `environ`, it'll get this version of
+/// `__wasilibc_environ`, which isn't initialized with a constructor function.
+/// `getenv` etc. call `__wasilibc_ensure_environ()` before accessing it.
+/// Statically-initialize it to an invalid pointer value so that we can
+/// detect if it's been explicitly initialized (we can't use `NULL` because
+/// `clearenv` sets it to NULL.
+weak char **__wasilibc_environ = (char **)-1;
+
+// See the comments in libc-environ.h.
+void __wasilibc_ensure_environ(void) {
+    if (__wasilibc_environ == (char **)-1) {
+        __wasilibc_initialize_environ();
+    }
+}
+
+/// Avoid dynamic allocation for the case where there are no environment
+/// variables, but we still need a non-NULL pointer to an (empty) array.
+static char *empty_environ[1] = { NULL };
+
+// See the comments in libc-environ.h.
+void __wasilibc_initialize_environ(void) {
+    // Get the sizes of the arrays we'll have to create to copy in the environment.
+    size_t environ_count;
+    size_t environ_buf_size;
+    __wasi_errno_t err = __wasi_environ_sizes_get(&environ_count, &environ_buf_size);
+    if (err != __WASI_ERRNO_SUCCESS) {
+        goto oserr;
+    }
+    if (environ_count == 0) {
+        __wasilibc_environ = empty_environ;
+        return;
+    }
+
+    // Add 1 for the NULL pointer to mark the end, and check for overflow.
+    size_t num_ptrs = environ_count + 1;
+    if (num_ptrs == 0) {
+        goto software;
+    }
+
+    // Allocate memory for storing the environment chars.
+    char *environ_buf = malloc(environ_buf_size);
+    if (environ_buf == NULL) {
+        goto software;
+    }
+
+    // Allocate memory for the array of pointers. This uses `calloc` both to
+    // handle overflow and to initialize the NULL pointer at the end.
+    char **environ_ptrs = calloc(num_ptrs, sizeof(char *));
+    if (environ_ptrs == NULL) {
+        free(environ_buf);
+        goto software;
+    }
+
+    // Fill the environment chars, and the `__wasilibc_environ` array with
+    // pointers into those chars.
+    // TODO: Remove the casts on `environ_ptrs` and `environ_buf` once the witx is updated with char8 support.
+    err = __wasi_environ_get((uint8_t **)environ_ptrs, (uint8_t *)environ_buf);
+    if (err != __WASI_ERRNO_SUCCESS) {
+        free(environ_buf);
+        free(environ_ptrs);
+        goto oserr;
+    }
+
+    __wasilibc_environ = environ_ptrs;
+    return;
+oserr:
+    _Exit(EX_OSERR);
+software:
+    _Exit(EX_SOFTWARE);
+}
+
+// See the comments in libc-environ.h.
+void __wasilibc_deinitialize_environ(void) {
+    if (__wasilibc_environ != (char **)-1) {
+        // Let libc-top-half clear the old environment-variable strings.
+        clearenv();
+        // Set the pointer to the special init value.
+        __wasilibc_environ = (char **)-1;
+    }
+}
+
+// See the comments in libc-environ.h.
+weak void __wasilibc_maybe_reinitialize_environ_eagerly(void) {
+    // This version does nothing. It may be overridden by a version which does
+    // something if `environ` is used.
+}