match-bss-segment

name	match-bss-segment
description	Match a segment's bss data by replacing extern declarations with the appropriate definitions. Use when asked to match, add, split, or fix a .bss segment, especially after checksum failures from bss symbol layout, shifted VRAM labels, queue/stack buffers, or unresolved bss externs.

Match BSS Segment

Core Rule

Match .bss by reproducing the original VRAM layout exactly. A successful local compile is not enough; the full ROM checksum must match.

Use symbol_addrs.txt as the main layout source. Use code references to infer types and sizes, but let the expected VRAM addresses decide ordering, padding, arrays, and segment boundaries.

Workflow

1. Identify the target range.

   • Find the target symbols in symbol_addrs.txt.
   • Note the first symbol address, each following symbol address, and the first symbol after the target file's range.
   • Check snowboardkids.yaml for the current unsplit bss segment covering that range.

2. Split snowboardkids.yaml.

   • Add a .bss subsegment for the C file at the first target symbol VRAM.
   • Preserve the remaining unknown range by adding or keeping a trailing plain bss segment at the next unclaimed VRAM.
   • Keep later known .bss or lib .bss entries at their original VRAMs.

Example:

- { type: .bss, vram: 0x800A35D0, name: system/thread_manager }
- { type: .bss, vram: 0x800A4460, name: audio/audio_manager }

3. Replace externs in the C file.

   • Convert only symbols that belong to the target file's .bss range from extern declarations to definitions.
   • Add __attribute__((section(".bss"))) to each definition.
   • Use explicit zero initialization so definitions are emitted in source order instead of as reorderable common symbols, e.g. s32 foo __attribute__((section(".bss"))) = 0; or u8 buffer[0x10] __attribute__((section(".bss"))) = { 0 };.
   • Order definitions by expected VRAM address, not by where the old externs happened to appear.
   • Use static only when the symbol is file-local and not referenced externally.
   • Keep unrelated externs as externs.

4. Infer sizes from address deltas and use sites.

   • For adjacent symbols, subtract addresses to infer object sizes.
   • For stacks, define the full stack array and pass stack + sizeof(stack) to osCreateThread.
   • For OSMesgQueue buffers, define arrays sized to the queue depth passed to osCreateMesgQueue; pass the array base, not &array.
   • For gaps that are not understood, add a named or static padding array only when needed to preserve layout.
   • Prefer real structs and arrays over u8 padding[] when usage reveals the type.
   • Check whether autogenerated asm labels fall inside a larger real object. If a struct's size spans those labels, let the struct own that range and do not add standalone padding for labels inside it.

5. Fix shifted label names caused by newly split earlier bss.

   • Matching an earlier .bss range can change autogenerated suffixes such as D_800A6468_A7068 to D_800A6468_A7058.
   • Search the whole project for old shifted names and update references consistently.
   • Do not create duplicate declarations under old and new names.

6. Build and compare layout.

   • Run ./tools/build-and-verify.sh.
   • If the checksum fails, inspect generated addresses:

mips-linux-gnu-nm -n build/snowboardkids.elf | rg "symbolA|symbolB|target_file"

• Compare against symbol_addrs.txt. If one symbol is correct and all later symbols are too early or late, the preceding symbol's size is wrong.
• If symbols appear reordered by alignment rather than source order, check for tentative definitions without explicit zero initialization.
• Re-check array lengths, implicit alignment, struct size, and missing padding before changing YAML addresses.

7. Finish only after full verification.
   • ./tools/build-and-verify.sh must finish with build/snowboardkids.z64: OK.
   • If the user requested a commit, commit only the scoped YAML and source changes after the verifier passes.
   • If the build script explicitly says to stop, stop immediately and report the best known state rather than attempting another change.

Common Patterns

Single cached object

OutputStruct_19E80 gCachedSpriteTextureEntry __attribute__((section(".bss")));

Queue backing buffer

OSMesgQueue displayQueue __attribute__((section(".bss")));
OSMesg displayQueueMsgs[0x20] __attribute__((section(".bss")));

osCreateMesgQueue(&displayQueue, displayQueueMsgs, 0x20);

Thread stack

OSThread audioThread __attribute__((section(".bss")));
char audioThreadStack[0x180] __attribute__((section(".bss")));

osCreateThread(&audioThread, 9, audioThreadEntry, 0, audioThreadStack + sizeof(audioThreadStack), 7);

Quality Checks

• Do not use manual pointer arithmetic to fake struct fields.
• Do not make unclear symbols void * when code usage reveals a real type.
• Keep macro definitions, structs, globals, declarations, and implementations in project order.
• Search src/ and include/ for duplicate or stale declarations before final verification.
• Update DECOMPILATION_LEARNINGS.md only when matching reveals a reusable compiler or project-specific insight.