Allocate the argv buffers with alloca instead of malloc.

libc-bottom-half/sources/__original_main.c

@@ -1,5 +1,6 @@
 #include <wasi/core.h>
 #include <wasi/libc.h>
+#include <alloca.h>
 #include <stdlib.h>
 #include <sysexits.h>
 
@@ -27,27 +28,24 @@ int __original_main(void) {
  }
 
  // Allocate memory for storing the argument chars.
- char *argv_buf = malloc(argv_buf_size);
- if (argv_buf == NULL) {
- _Exit(EX_SOFTWARE);
- }
+ char *argv_buf = alloca(argv_buf_size);
 
- // Allocate memory for the array of pointers. This uses `calloc` both to
- // handle overflow and to initialize the NULL pointer at the end.
- char **argv = calloc(num_ptrs, sizeof(char *));
- if (argv == NULL) {
- free(argv_buf);
+ // Allocate memory for the array of pointers.
+ size_t num_ptrs_size;
+ if (__builtin_mul_overflow(num_ptrs, sizeof(char *), &num_ptrs_size)) {
  _Exit(EX_SOFTWARE);
  }
+ char **argv = alloca(num_ptrs_size);
 
  // Fill the argument chars, and the argv array with pointers into those chars.
  err = __wasi_args_get(argv, argv_buf);
  if (err != __WASI_ESUCCESS) {
- free(argv_buf);
- free(argv);
  _Exit(EX_OSERR);
  }
 
+ // Make sure the last pointer in the array is NULL.
+ argv[argc] = NULL;
+
  // Call main with the arguments!
  return main(argc, argv);
 }