pkgs/applications/virtualization/qemu/binfmt-p-wrapper.c

   1 // This is a tiny wrapper that converts the extra arv[0] argument
   2 // from binfmt-misc with the P flag enabled to QEMU parameters.
   3 // It also prevents LD_* environment variables from being applied
   4 // to QEMU itself.
   5
   6 #include <stdio.h>
   7 #include <stdlib.h>
   8 #include <string.h>
   9 #include <unistd.h>
  10
  11 #ifndef TARGET_QEMU
  12 #error "Define TARGET_QEMU to be the path to the qemu-user binary (e.g., -DTARGET_QEMU=\"/full/path/to/qemu-riscv64\")"
  13 #endif
  14
  15 extern char **environ;
  16
  17 int main(int argc, char *argv[]) {
  18     if (argc < 3) {
  19         fprintf(stderr, "%s: This should be run as the binfmt interpreter with the P flag\n", argv[0]);
  20         fprintf(stderr, "%s: My preconfigured qemu-user binary: %s\n", argv[0], TARGET_QEMU);
  21         return 1;
  22     }
  23
  24     size_t environ_count = 0;
  25     for (char **cur = environ; *cur != NULL; ++cur) {
  26         environ_count++;
  27     }
  28
  29     size_t new_argc = 3;
  30     size_t new_argv_alloc = argc + 2 * environ_count + 2; // [ "-E", env ] for each LD_* env + [ "-0", argv0 ]
  31     char **new_argv = (char**)malloc((new_argv_alloc + 1) * sizeof(char*));
  32     if (!new_argv) {
  33         fprintf(stderr, "FATAL: Failed to allocate new argv array\n");
  34         abort();
  35     }
  36
  37     new_argv[0] = TARGET_QEMU;
  38     new_argv[1] = "-0";
  39     new_argv[2] = argv[2];
  40
  41     // Pass all LD_ env variables as -E and strip them in `new_environ`
  42     size_t new_environc = 0;
  43     char **new_environ = (char**)malloc((environ_count + 1) * sizeof(char*));
  44     if (!new_environ) {
  45         fprintf(stderr, "FATAL: Failed to allocate new environ array\n");
  46         abort();
  47     }
  48
  49     for (char **cur = environ; *cur != NULL; ++cur) {
  50         if (strncmp("LD_", *cur, 3) == 0) {
  51             new_argv[new_argc++] = "-E";
  52             new_argv[new_argc++] = *cur;
  53         } else {
  54             new_environ[new_environc++] = *cur;
  55         }
  56     }
  57     new_environ[new_environc] = NULL;
  58
  59     size_t new_arg_start = new_argc;
  60     new_argc += argc - 3 + 2; // [ "--", full_binary_path ]
  61
  62     if (argc > 3) {
  63         memcpy(&new_argv[new_arg_start + 2], &argv[3], (argc - 3) * sizeof(char**));
  64     }
  65
  66     new_argv[new_arg_start] = "--";
  67     new_argv[new_arg_start + 1] = argv[1];
  68     new_argv[new_argc] = NULL;
  69
  70 #ifdef DEBUG
  71     for (size_t i = 0; i < new_argc; ++i) {
  72         fprintf(stderr, "argv[%zu] = %s\n", i, new_argv[i]);
  73     }
  74 #endif
  75
  76     return execve(new_argv[0], new_argv, new_environ);
  77 }
  78
  79 // vim: et:ts=4:sw=4