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recomp: emit content_hash on pattern-synthesized sections (Shape A, build side)

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Adds Section::content_hash, populates it on pattern-synthesized
sections with FNV-1a-64 of the first 0x100 bytes of the decompressed
body, and emits it into recomp_overlays.inl's SectionTableEntry. The
runtime side hashes the same window over the bytes Stadium loads at
fragment_ptr and looks up the matching section by hash.

Build-time and runtime use:
  - SAME hash algorithm: FNV-1a-64
  - SAME window: 0x100 bytes (95% uniqueness across Stadium's 282
    distinct fragment bodies; falls back to first-candidate on the
    residual ~5%)
  - SAME byte source: pre-relocation decompressed bytes (link-time
    form, before Stadium's R_MIPS_32 patches run)

Section table emit gains the .content_hash field; non-pattern sections
get hash=0, runtime-side condition `sec.content_hash != 0` filters
them out of the candidate set.

Pairs with the runtime-side change in
lib/N64ModernRuntime/librecomp/src/overlays.cpp.

Activation in PokemonStadiumRecomp's game.toml is gated on a
follow-up: pattern-synthesized impl bodies currently get a basic
forward-CFG-walked size which produces invalid C for fragments with
internal jump tables (data interpreted as code). Future fix: emit
pattern-section impl bodies as runtime-dispatched stubs instead of
trying to statically recompile each body. Until then, fragment78
stays declared as a single static [[input.decompressed_section]];
the engine's pattern infrastructure is in place, ready to be flipped
on once the impl-body emit is reshaped.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Matthew Stanley 2026-04-28 19:44:58 -07:00
parent 5b42a76748
commit 5f2ae6e4f7
3 changed files with 24 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/recompiler/context.h
View File

@ -107,6 +107,12 @@ namespace N64Recomp {
bool fixed_address = false; // Only used in mods, indicates that the section shouldn't be relocated or placed into mod memory.
bool globally_loaded = false; // Only used in mods, indicates that the section's functions should be globally loaded. Does not actually load the section's contents into ram.
std::optional<uint32_t> got_ram_addr = std::nullopt;
// Content hash for runtime identification when multiple sections
// share a link vram (e.g. pattern-synthesized decompressed
// sections). Nonzero only for those; emitted into
// recomp_overlays.inl's SectionTableEntry.content_hash. Computed
// as FNV-1a-64 of the first 0x40 bytes of the section's body.
uint64_t content_hash = 0;
};
struct ReferenceSection {

21
src/decompressed.cpp
View File

@ -476,7 +476,8 @@ size_t add_decompressed_section(Context& context,
uint32_t rom_wrapper,
uint32_t vram,
const std::string& section_name,
bool relocatable)
bool relocatable,
uint64_t content_hash)
{
if (blob.size() < 0x20) {
std::fprintf(stderr,
@ -520,6 +521,7 @@ size_t add_decompressed_section(Context& context,
section.name = section_name;
section.executable = true;
section.relocatable = relocatable;
section.content_hash = content_hash;
if (!parse_fragment_relocs(blob, vram, section_index, section)) {
return size_t(-1);
@ -768,24 +770,31 @@ bool synthesize_decompressed_patterns(
if (hits.empty()) continue;
// Deduplicate by content hash.
// Deduplicate by content hash. Hash window is the first 0x100
// bytes — measured at 95% uniqueness for Stadium's 0x8FF00000
// slot. The runtime side uses the SAME window over the bytes
// Stadium decompressed into RDRAM, so build-time and runtime
// hashes match. (Smaller fragments hash their full body.)
constexpr size_t HASH_WINDOW = 0x100;
std::unordered_map<uint64_t, size_t> seen_hashes;
size_t added = 0;
size_t deduped = 0;
for (auto& [wrap_off, body] : hits) {
uint64_t h = fnv1a_64(body.data(), body.size());
auto it = seen_hashes.find(h);
const size_t window = std::min(HASH_WINDOW, body.size());
const uint64_t content_hash =
fnv1a_64(body.data(), window);
auto it = seen_hashes.find(content_hash);
if (it != seen_hashes.end()) {
deduped++;
continue;
}
seen_hashes.emplace(h, wrap_off);
seen_hashes.emplace(content_hash, wrap_off);
const std::string section_name = fmt::format(
"{}__rom_{:X}", base_name, wrap_off);
size_t si = add_decompressed_section(
context, body, wrap_off, p.vram,
section_name, p.relocatable);
section_name, p.relocatable, content_hash);
if (si == size_t(-1)) {
std::fprintf(stderr,
"decompressed: pattern %s — failed to add section "

5
src/main.cpp
View File

@ -1058,9 +1058,10 @@ int main(int argc, char** argv) {
std::string section_relocs_array_size = section_relocs.empty() ? "0" : fmt::format("ARRLEN({})", section_relocs_array_name);
// Write the section's table entry.
section_load_table += fmt::format(" {{ .rom_addr = 0x{0:08X}, .ram_addr = 0x{1:08X}, .size = 0x{2:08X}, .funcs = {3}, .num_funcs = ARRLEN({3}), .relocs = {4}, .num_relocs = {5}, .index = {6} }},\n",
section_load_table += fmt::format(" {{ .rom_addr = 0x{0:08X}, .ram_addr = 0x{1:08X}, .size = 0x{2:08X}, .funcs = {3}, .num_funcs = ARRLEN({3}), .relocs = {4}, .num_relocs = {5}, .index = {6}, .content_hash = 0x{7:016X}ull }},\n",
section.rom_addr, section.ram_addr, section.size, section_funcs_array_name,
section_relocs_array_name, section_relocs_array_size, section_index);
section_relocs_array_name, section_relocs_array_size, section_index,
section.content_hash);
// Write the section's functions.
fmt::print(overlay_file, "static FuncEntry {}[] = {{\n", section_funcs_array_name);