match-ultralib-segment

name	match-ultralib-segment
description	Match a given segment to a libultra ROM segment. Use this when converting unidentified asm libultra ranges such as osRecvMesg to matching C source.

Match an Ultralib Segment

Core Rules

• Match libultra by compiling local source under src/ultra; do not patch linker scripts, generated linker scripts, or archive-member references.
• Preserve the upstream libultra subdirectory when possible, for example ../ultralib/src/io/pfsnumfiles.c becomes src/ultra/io/pfsnumfiles.c.
• Keep unidentified neighboring libultra functions as separate asm segments until each function is matched as source.
• Source under src/ultra should use real libultra names, not func_... or D_... placeholders.
• Add required callable ROM symbols to symbol_addrs.txt with runtime VRAM addresses, not 0x700... splat placeholder addresses. Never add libultra function aliases to linker_scripts/libultra_syms.ld.
• If a libultra source file emits .data or .bss, match those sections in snowboardkids.yaml; do not remove the C definitions, make them extern, allow multiple definitions, add linker-script aliases, or delete generated linker entries.
• When asm references a field inside a known libultra struct, annotate the owning struct symbol in symbol_addrs.txt with its real type and size. Do not add a linker-script alias for the field address.

Workflow

1. Inspect the target function before trusting upstream source. Version-specific libultra code can differ from the checked-in upstream copy:

   python3 tools/asm-differ/diff.py --no-pager osPfsNumFiles
   

   Watch for local deltas such as extra initialization loops, literal stores, or changed command/status values.

2. Find the upstream source and headers:

   rg -n "osPfsNumFiles" ../ultralib/src ../ultralib/include
   

3. Copy or port the upstream file into src/ultra, preserving the source subtree. Verify macro values in local headers before using semantic-looking names; for example CONT_CMD_NOP may be 0xff, while the target may want a literal 0. Treat the upstream as a starting point — the compiled ROM may have been built from a different version of the source. Build early and let the diff guide iterations rather than analyzing the assembly exhaustively beforehand.

   ../ultralib/src/os/recvmesg.c -> src/ultra/os/recvmesg.c
   ../ultralib/src/io/pfsnumfiles.c -> src/ultra/io/pfsnumfiles.c
   

4. Replace the matching ROM range in snowboardkids.yaml with a normal C segment:

   - [0xA1590, c, ultra/os/recvmesg]
   - [0xA2650, c, ultra/io/pfsnumfiles]
   

5. If the new source object emits .data or .bss, match those sections before trying linker workarounds. First inspect the object:

   mips-linux-gnu-objdump -h build/src/ultra/os/initialize.o
   mips-linux-gnu-nm -n build/src/ultra/os/initialize.o
   

   Then split the existing raw data/BSS ranges in snowboardkids.yaml so the C file owns exactly the emitted data. Keep the definitions in C when they are part of the upstream file; changing them to extern can alter IDO codegen even when it looks semantically equivalent.

   Example for ultra/os/initialize, whose .data lives inside B1C00.data.s and whose .bss lives inside the main BSS block:

   - [0xB1C00, data]
   - [0xDFED0, .data, ultra/os/initialize]
   - [0xDFEF0, data]
   ...
   - { type: bss, name: bss_chunk_a, vram: 0x800E29C0 }
   - { type: .bss, name: ultra/os/initialize, vram: 0x8015CCD0 }
   - { type: bss, name: bss_chunk_b, vram: 0x8015CCE0 }
   

   For initialize.c, the matched .data range is 0xDFED0..0xDFEF0 and contains osClockRate, osViClock, __osShutdown, and __OSGlobalIntMask. is BSS at . The raw ranges before and after remain raw segments; give split BSS chunks stable names so Splat does not collapse or mis-name them.

6. If the new source calls functions or references data already present elsewhere in the ROM, add the real ultralib symbol names to symbol_addrs.txt. Avoid using aliases to make the work with unlabeled symbols (those starting with D_ or func_). Important: symbols with 0x700... addresses are splat placeholders and must be converted to runtime 0x800... VRAM addresses before the linker can resolve them. A linker-script alias such as osSendMesg = 0x800A0D30; in linker_scripts/libultra_syms.ld is the wrong fix; update symbol_addrs.txt, the real asm/C labels, and call sites instead. Scan for any 0x700A entries that the new source calls:

   __osDisableInt = 0x800A61B0; // type:func
   __osRestoreInt = 0x800A61D0; // type:func
   __osContPifRam = 0x8015CA00;
   

   Before moving on, verify that no libultra function alias was added to the linker scripts, and that the matched/called functions use real names instead of address-derived placeholders:

   rg -n "= 0x800A" linker_scripts
   rg -n "func_800A[0-9A-Fa-f]+" symbol_addrs.txt src asm
   

   If the second command finds unrelated existing placeholders, do not rename them blindly. Fix only the symbols involved in the segment being matched.

7. If asm references an address inside a known libultra struct, fix the owning symbol metadata instead of creating a standalone D_... symbol. The desired output is an addend reference such as %hi(__osPiDevMgr + 0x8), not a generated field label and not a linker-script alias.

   Example: 0x800DF2F8 is __osPiDevMgr.cmdQueue, where __osPiDevMgr starts at 0x800DF2F0 and OSDevMgr.cmdQueue is at offset 0x8. Annotate the struct:

   __osPiDevMgr = 0x800DF2F0; // type:OSDevMgr size:0x1C
   

   Then regenerate/extract as needed and verify the asm uses the base symbol plus addend:

   rg -n "D_800DF2F8|__osPiDevMgr \\+ 0x8" asm symbol_addrs.txt linker_scripts
   

   Do not add this to linker_scripts/libultra_syms.ld:

   D_800DF2F8 = 0x800DF2F8;
   

   The struct size should come from the header layout and the observed next symbol or BSS/data range. For OSDevMgr, the fields are seven 4-byte words, so the size is 0x1C.

8. Build and verify:

   ./tools/build-and-verify.sh
   

9. If verification fails, diff every function emitted by the new source before looking for linker or data issues:

   python3 tools/asm-differ/diff.py --no-pager osPfsNumFiles
   

10. Document Learnings:

Update the DECOMPILATION_LEARNINGS.md file in the root of the project with any additional learnings that you gathered as part of matching this segment. Only add generic, broadly applicable lessons — things that would help when matching a different function in the future. Do not add per-file details such as specific VRAM/ROM addresses, individual symbol names, exact segment split locations, or step-by-step accounts of what happened for one particular function. Ask: "would this lesson help me match an unrelated ultra function tomorrow?" If not, leave it out.

Build Flags

The game code uses -O2 but ultralib specifically should use -O1 instead. The build version can also affect libultra behavior, so check the compile line for both -O1 and the expected BUILD_VERSION such as BUILD_VERSION=VERSION_I. You can use the following pattern to override the flags:

$(BUILD_DIR)/src/ultra/io/%.o: C_OPT = -O1

VERSION_I Specifics

This project uses BUILD_VERSION=VERSION_I. When porting upstream ultralib source, apply these adjustments:

• __osPfsSelectBank takes 1 argument (OSPfs*), not 2. The SELECT_BANK macro sets pfs->activebank then calls __osPfsSelectBank(pfs).
• No __osPfsCheckRamArea function — skip any BUILD_VERSION >= VERSION_J blocks that call it.
• Uses for loops instead of bcopy for memory copies.
• No PFS_ID_BROKEN status flag handling.
• The upstream source may contain calls that were not present in the actual VERSION_I build. Trust the assembly over the upstream — if a call appears in upstream but not in the target assembly, omit it.

Incorrect Segments

Be mindful that you may need to adjust the start/end points of segments as well as the segment name to match it to the correct ultralib c file.

Data, Rodata, and BSS Matching

Ultralib segments may contain data, rodata, and/or bss which must be similarly matched. These are likely unlabelled. You will need to find the appropriate data/rodata/bss segment and link it back to your matched ultralib segment, e.g:

- [0xDFED0, .data, ultra/os/initialize]
- [0xE15B0, .rodata, myUltraLibSegment]
- { type: .bss, name: ultra/os/initialize, vram: 0x8015CCD0 }

First check whether the compiled object actually emits these sections:

mips-linux-gnu-objdump -h build/src/ultra/io/pfsnumfiles.o

If the object only has .text plus compiler metadata such as .options and .reginfo, continue matching instruction generation before adding data or rodata segments.

If the object emits data/BSS that already exists in a broad raw segment, split the broad segment around the emitted range. Do not use linker scripts to alias the symbols or Makefile commands to strip sections out of the generated linker script. Keep the C definitions and let the corresponding .data/.bss YAML entries own those sections.

You can use the match-data-file skill to help match the correct segment. Note that it might not be properly annotated (yet) in snowboardkids.yaml.

Avoid

• Do not mutate linker scripts with perl -0pi, perl -pe, or similar build hacks.
• Do not edit the Makefile to sed generated linker scripts or add --allow-multiple-definition to hide duplicate data.
• Do not add libultra function aliases to linker_scripts/libultra_syms.ld; define the symbol in symbol_addrs.txt at its runtime 0x800... address and rename the real labels/references.
• Do not add libultra data aliases to linker_scripts/libultra_syms.ld; match the data/BSS section in snowboardkids.yaml.
• Do not add linker-script aliases for struct field addresses such as D_800DF2F8. Annotate the owning symbol with type: and size: in symbol_addrs.txt so asm can reference symbol + offset.
• Do not change real libultra data definitions to extern just to avoid duplicate storage; it can change IDO codegen. Match the emitted data/BSS segments instead.
• Do not replace archive-member linker entries by text substitution.
• Do not link libultra_rom.a just to extract one matched object.
• Do not add a custom symbol_addrs.ld; use symbol_addrs.txt.
• Do not disable undefined_funcs_auto.txt to keep a local libultra source dependency unresolved.
• Do not leave func_... or D_... references in src/ultra.