Differences

This shows you the differences between two versions of the page.

@@ Line 1: / Line 1: @@
+====== Overlay Files ======
+Yoshi's Story uses overlays to save memory. The structure of an overlay file is as follows:
+<code C>
+u8  text[textSize]
+u8  data[dataSize]
+u8  rodata[rodataSize]
+meta {
+    u32 textSize
+    u32 dataSize
+    u32 rodataSize
+    u32 bssSize
+    u32 numRelocations
+    u32 relocations[numRelocations]
+}
+u32 metaSize
+</code>
+  * The position of the meta section is calculated by subtracting metaSize from the total size of the overlay file.
+  * The .bss section is allocated immediately after the overlay file in memory.
+Relocation bitfields:
+<code>ss -- rrrr oooooooooooooooooooooooo</code>
+^Bitfield^Description^
+|s|Section (0 = invalid?, 1 = .text, 2 = .data, 3 = .rodata)|
+|-|Unused?|
+|r|Relocation type (4 = R_MIPS_26, 5 = R_MIPS_HI16, 6 = R_MIPS_LO16)|
+|o|Offset|
+The dynamic linker routine is located at 0x80081430 in RAM.
+<code C>func_80081430(void *overlay_block, void *meta_section);</code>
+The game keeps track of active overlays using an array of the following struct at 0x800DA840 in RAM.
+<code C>
+struct OverlayEntry
+{
+    /*00*/ void *location;     // actual location in memory
+    /*04*/ u16   objectId;     // id of the object that this overlay belongs to
+           u8    _pad[2];
+    /*08*/ void *fakeMemStart; // fake start address
+    /*0C*/ void *fakeMemEnd;   // fake end address
+};
+</code>