1 files changed, 25 insertions, 3 deletions

diff --git a/tools/br_ips/ips_patch.c b/tools/br_ips/ips_patch.c
index 03780cf72..506f23ad7 100644
--- a/tools/br_ips/ips_patch.c
+++ b/tools/br_ips/ips_patch.c
@@ -24,18 +24,36 @@ do {                                        \
 static const char SPLASH[] = "Small IPS patch utility\n"
                              "Created by PikalaxALT on 23 June 2019 All Rights Reserved\n";
 
+static const char HELP[] = "ips_patch [-h] ROM PATCH OUT\n"
+                           "\n"
+                           "    ROM - input ROM file\n"
+                           "    PATCH - IPS patch file to apply\n"
+                           "    OUT - path to write patched ROM\n"
+                           "\n"
+                           "Options:\n"
+                           "    -h - show this message and exit\n";
+
 int main(int argc, char ** argv) {
+    // Show a friendly message
     puts(SPLASH);
-    if (argc != 4) FATAL_ERROR("usage: %s ROM PATCH OUT\n", argv[0]);
+    // If requested, show help message
+    if (argc >= 2 && strcmp(argv[1], "-h") == 0) {
+        puts(HELP);
+        return 0;
+    }
+    // Enforce CLI syntax
+    if (argc != 4) FATAL_ERROR("usage: %s [-h] ROM PATCH OUT\n", argv[0]);
     FILE * rom = fopen(argv[1], "rb");
     if (rom == NULL) FATAL_ERROR("failed to open file \"%s\" for reading\n", argv[1]);
     FILE * patch = fopen(argv[2], "rb");
     if (patch == NULL) FATAL_ERROR("failed to open file \"%s\" for reading\n", argv[2]);
     FILE * out = fopen(argv[3], "wb");
     if (patch == NULL) FATAL_ERROR("failed to open file \"%s\" for writing\n", argv[3]);
+    // IPS magic header
     char magic[5];
     if (fread(magic, 1, 5, patch) != 5) FATAL_ERROR("read magic\n");
     if (memcmp(magic, "PATCH", 5) != 0) FATAL_ERROR("malformed IPS patch\n");
+    // Read the ROM into allocated memory.
     fseek(rom, 0, SEEK_END);
     size_t romsize = ftell(rom);
     fseek(rom, 0, SEEK_SET);
@@ -46,16 +64,20 @@ int main(int argc, char ** argv) {
     while (1) {
         uint32_t offset;
         size_t size;
-        
+        // Read each hunk into the buffer, overwriting previous data.
+        // If two or more hunks overlap, the newest one is retained.
+        // A good IPS patch creator will avoid this.
         offset = (unsigned char)getc(patch) << 16;
         offset |= (unsigned char)getc(patch) << 8;
         offset |= (unsigned char)getc(patch);
-        if (offset == 0x454F46) break;
+        if (offset == 0x454F46) break; // end sentinel "EOF"
         size = (unsigned char)getc(patch) << 8;
         size |= (unsigned char)getc(patch);
+        if (offset + size > romsize) FATAL_ERROR("segment extends past end of ROM\n");
         if (fread(buffer + offset, 1, size, patch) != size) FATAL_ERROR("read segment\n");
     }
     fclose(patch);
+    // Write the patched ROM
     fwrite(buffer, 1, romsize, out);
     fclose(out);
     free(buffer);