Allow loading more than one ELF binary

This makes it easier to use a separate M-mode bootloader and kernel
payload (e.g. OpenSBI fw_jump). It also makes it easier to test booting
systems such as FreeBSD without bundling the kernel with the bootloader.

c_emulator/riscv_sim.c

@@ -142,12 +142,9 @@ static struct option options[] = {
 
 static void print_usage(const char *argv0, int ec)
 {
+  fprintf(stdout, "Usage: %s [options] <elf_file> [<elf_file> ...]\n", argv0);
 #ifdef RVFI_DII
-  fprintf(stdout,
-          "Usage: %s [options] <elf_file>\n       %s [options] -r <port>\n",
-          argv0, argv0);
-#else
-  fprintf(stdout, "Usage: %s [options] <elf_file>\n", argv0);
+  fprintf(stdout, "       %s [options] -r <port>\n", argv0);
 #endif
   struct option *opt = options;
   while (opt->name) {
@@ -218,8 +215,11 @@ static void read_dtb(const char *path)
 }
 
 /**
- * Parses the command line arguments and returns the argv index for the ELF file
- * that should be loaded.
+ * Parses the command line arguments and returns the argv index for the first
+ * ELF file that should be loaded. As getopt transforms the argv array, all
+ * argv values following that index are non-options and can be treated as
+ * additional ELF files that should be loaded into memory (but not scanned
+ * for the magic tohost/{begin,end}_signature symbols).
  */
 static int process_args(int argc, char **argv)
 {
@@ -1027,7 +1027,7 @@ int main(int argc, char **argv)
   preinit_sail();
 
   int files_start = process_args(argc, argv);
-  char *file = argv[files_start];
+  char *initial_elf_file = argv[files_start];
   init_logs();
 
   if (gettimeofday(&init_start, NULL) < 0) {
@@ -1093,15 +1093,29 @@ int main(int argc, char **argv)
     }
     printf("Connected\n");
   } else
-    entry = load_sail(file);
+    entry = load_sail(initial_elf_file);
 #else
-  uint64_t entry = load_sail(file);
+  uint64_t entry = load_sail(initial_elf_file);
 #endif
+  /* Load any additional ELF files into memory */
+  for (int i = files_start + 1; i < argc; i++) {
+    bool is32bit;
+    uint64_t additional_entry;
+    fprintf(stdout, "Loading additional ELF file %s.\n", argv[i]);
+    /*
+     * We use load_elf() directly instead of load_sail() as we do not want to
+     * override tohost/{begin,end}_signature from the initial ELF file.
+     */
+    load_elf(argv[i], &is32bit, &additional_entry);
+    check_elf(is32bit);
+    fprintf(stdout, "Additional ELF %d Entry @ 0x%" PRIx64 "\n",
+            i - files_start, additional_entry);
+  }
 
   /* initialize spike before sail so that we can access the device-tree blob,
    * until we roll our own.
    */
-  init_spike(file, entry, rv_ram_size);
+  init_spike(initial_elf_file, entry, rv_ram_size);
   init_sail(entry);
 
   if (!init_check(s))