Remove 0xFF padding from uncompressed ROMs (#1910)

* Remove 0xFF padding from uncompressed ROMs

* Add comment about overdump contents

* Update checksum in README

* Reword comment

README.md

@@ -29,7 +29,7 @@ The only build currently supported is Master Quest (Debug), but other versions a
 
 It builds the following ROM:
 
-* oot-gc-eu-mq-dbg.z64 `md5: f0b7f35375f9cc8ca1b2d59d78e35405`
+* oot-gc-eu-mq-dbg.z64 `md5: 75e344f41c26ec2ec5ad92caa9e25629`
 
 **Note: This repository does not include any of the assets necessary to build the ROM. A prior copy of the game is required to extract the needed assets.**
 

baseroms/gc-eu-mq-dbg/checksum.md5

@@ -1 +1 @@
-f0b7f35375f9cc8ca1b2d59d78e35405  build/gc-eu-mq-dbg/oot-gc-eu-mq-dbg.z64
+75e344f41c26ec2ec5ad92caa9e25629  build/gc-eu-mq-dbg/oot-gc-eu-mq-dbg.z64

baseroms/gc-eu-mq/checksum.md5

@@ -1 +1 @@
-1a438f4235f8038856971c14a798122a  build/gc-eu-mq/oot-gc-eu-mq.z64
+4920520254b9aab86de57b42ab477dbb  build/gc-eu-mq/oot-gc-eu-mq.z64

tools/decompress_baserom.py

@@ -88,9 +88,10 @@ def decompress_rom(
         dma_entry.to_bin(entry_data)
         decompressed.write(entry_data)
     # pad to size
-    padding_end = round_up(dma_entries[-1].vrom_end, 14)
-    decompressed.seek(padding_end - 1)
-    decompressed.write(bytearray([0]))
+    padding_start = dma_entries[-1].vrom_end
+    padding_end = round_up(padding_start, 12)
+    decompressed.seek(padding_start)
+    decompressed.write(b"\x00" * (padding_end - padding_start))
     # re-calculate crc
     return bytearray(update_crc(decompressed).getbuffer())
 
@@ -127,9 +128,10 @@ def byte_swap(file_content: bytearray) -> bytearray:
 
 def per_version_fixes(file_content: bytearray, version: str) -> bytearray:
     if version == "gc-eu-mq-dbg":
-        # Strip the overdump
+        # Strip the overdump, which consists of an area of 0xFF bytes (which may
+        # be erased flash memory) and ROM data from an unrelated game
         print("Stripping overdump...")
-        file_content = file_content[0:0x3600000]
+        file_content = file_content[0:0x035CF000]
 
         # Patch the header
         print("Patching header...")
@@ -137,15 +139,6 @@ def per_version_fixes(file_content: bytearray, version: str) -> bytearray:
     return file_content
 
 
-def pad_rom(file_content: bytearray, dma_entries: list[dmadata.DmaEntry]) -> bytearray:
-    padding_start = round_up(dma_entries[-1].vrom_end, 12)
-    padding_end = round_up(dma_entries[-1].vrom_end, 14)
-    print(f"Padding from {padding_start:X} to {padding_end:X}...")
-    for i in range(padding_start, padding_end):
-        file_content[i] = 0xFF
-    return file_content
-
-
 # Determine if we have a ROM file
 ROM_FILE_EXTENSIONS = ["z64", "n64", "v64"]
 
@@ -227,8 +220,6 @@ def main():
             file_content, dmadata_start, dma_entries, is_zlib_compressed
         )
 
-    file_content = pad_rom(file_content, dma_entries)
-
     # Check to see if the ROM is a "vanilla" ROM
     str_hash = get_str_hash(file_content)
     if str_hash != correct_str_hash:
@@ -237,7 +228,7 @@ def main():
         )
 
         if version == "gc-eu-mq-dbg":
-            if str_hash == "32fe2770c0f9b1a9cd2a4d449348c1cb":
+            if str_hash == "9fede30e3239558cf3993f12b7ed7458":
                 print(
                     "The provided baserom is a rom which has been edited with ZeldaEdit and is not suitable for use with decomp. Find a new one."
                 )

tools/elf2rom.c

@@ -33,12 +33,6 @@ static bool parse_number(const char *str, int *num)
     return endptr > str;
 }
 
-static unsigned int round_up(unsigned int num, unsigned int multiple)
-{
-    num += multiple - 1;
-    return num / multiple * multiple;
-}
-
 static char *sprintf_alloc(const char *fmt, ...)
 {
     va_list args;
@@ -163,11 +157,10 @@ static void parse_input_file(const char *filename)
     free(syms);
 }
 
-// Writes the N64 ROM, padding the file size to a multiple of 1 MiB
+// Writes the N64 ROM
 static void write_rom_file(const char *filename, int cicType)
 {
-    size_t fileSize = round_up(g_romSize, 0x100000);
-    uint8_t *buffer = calloc(fileSize, 1);
+    uint8_t *buffer = calloc(g_romSize, 1);
     int i;
     uint32_t chksum[2];
 
@@ -179,16 +172,13 @@ static void write_rom_file(const char *filename, int cicType)
         memcpy(buffer + g_romSegments[i].romStart, g_romSegments[i].data, size);
     }
 
-    // pad the remaining space with 0xFF
-    memset(buffer + g_romSize, 0xFF, fileSize - g_romSize);
-
     // write checksum
     if (!n64chksum_calculate(buffer, cicType, chksum))
         util_fatal_error("invalid cic type %i", cicType);
     util_write_uint32_be(buffer + 0x10, chksum[0]);
     util_write_uint32_be(buffer + 0x14, chksum[1]);
 
-    util_write_whole_file(filename, buffer, fileSize);
+    util_write_whole_file(filename, buffer, g_romSize);
     free(buffer);
 }