riscv_sim: Add command line arguments to enable or disable use of boot ROM.

This adds command line arguments --boot-rom and --no-boot-rom to
enable or disable the use of the boot ROM at the reset vector.  The
current behaviour (--boot-rom) initialises a small bit of memory at
the reset vector to set up argument registers and then jump to the
address specified by entry point of the ELF file.  With --no-boot-rom
the simulator just sets the initial PC to the entry point.  For
backwards compatibility the default is to use the boot-rom unless
NO_BOOT_ROM is defined during compilation.

Author: rmn30

c_emulator/riscv_sim.c

@@ -85,6 +85,13 @@ bool config_print_reg = true;
 bool config_print_mem_access = true;
 bool config_print_platform = true;
 bool config_print_rvfi = false;
+int config_use_boot_rom = 
+#ifdef NO_BOOT_ROM
+false
+#else
+true
+#endif
+;
 
 void set_config_print(char *var, bool val)
 {
@@ -145,6 +152,8 @@ static struct option options[] = {
     {"inst-limit",                  required_argument, 0, 'l'                     },
     {"enable-zfinx",                no_argument,       0, 'x'                     },
     {"enable-writable-fiom",        no_argument,       0, OPT_ENABLE_WRITABLE_FIOM},
+    {"boot-rom",                    no_argument, &config_use_boot_rom, true},
+    {"no-boot-rom",                 no_argument, &config_use_boot_rom, false},
 #ifdef SAILCOV
     {"sailcov-file",                required_argument, 0, 'c'                     },
 #endif
@@ -159,10 +168,10 @@ static void print_usage(const char *argv0, int ec)
 #endif
   struct option *opt = options;
   while (opt->name) {
-    if (isprint(opt->val))
+    if (opt->flag == NULL)
       fprintf(stdout, "\t -%c\t --%s\n", (char)opt->val, opt->name);
     else
-      fprintf(stdout, "\t   \t --%s\n", opt->name);
+      fprintf(stdout, "\t\t --%s\n", opt->name);
     opt++;
   }
   exit(ec);
@@ -620,7 +629,11 @@ void init_sail(uint64_t elf_entry)
     zPC = elf_entry;
   } else
 #endif
+  if (config_use_boot_rom) {
     init_sail_reset_vector(elf_entry);
+  } else {
+    zPC = elf_entry;
+  }
 
   // this is probably unnecessary now; remove
   if (!rv_enable_rvc)