[loader] add ZBIC (zstd variant) NSO decompression support for Switch 22.0+ (#4482)

- [x] I have read and followed the [Contribution Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/CONTRIBUTING.md#code-contributions).
- [x] I have read and followed the [AI Policy](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/docs/policies/AI.md)
- [x] I have read and followed the [Coding Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/docs/policies/Coding.md) to the best of my ability.

-------------------
A new NSO compression method was introduced in Switch 22.0.0. This is a
customized variant of zstd and is used when NSO flags have bit 7 set.

Key characteristics:
  - ZSTD_MAGICNUMBER is set to 0x4349425A (b'ZBIC') instead of 0xFD2FB528
  - ZSTD_LEGACY_SUPPORT is set to 0
  - ZSTD_TRACE is set to 1, zstd version used is 1.5.7 (10507)
  - FSE_readNCount is replaced with a BIC (Binary Interpolative Coding)
    version which improves compression of entropy tables significantly

Source: https://switchbrew.org/wiki/22.0.0

Implementation:
  - Detect ZBIC segments via NSO flag bit 7 (NsoFlags_UseZbicCompression)
    and/or ZBIC magic scan in nso.cpp
  - Fall back to LZ4 when ZBIC is not detected or returns unexpected size
  - Handle segment 0 alternate offset (0x100 vs 0x108) for both ZBIC and LZ4

References:
  - Atmosphère loader/strat zstd-zbic integration:
    https://github.com/Atmosphere-NX/Atmosphere/commit/082115187a0509cb6b8a757de639a4e4741b8712
  - nxdumptool ZBIC segment compression support:
    https://github.com/DarkMatterCore/nxdumptool/commit/441e5c0904f29427987433be4eb057a2843d222a
  - STORM_SWITCH ZBIC implementation:
    https://github.com/ReiKatari/STORM_SWITCH/commit/1e09eb82b760aaf340b810031400991c0740c091

Tested with firmware 23.0.0 and ZBIC-compressed NSOs.

Co-authored-by: xbzk <xbzk@eden-emu.dev>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4482
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>
Reviewed-by: lizzie <lizzie@eden-emu.dev>
Reviewed-by: Maufeat <sahyno1996@gmail.com>

cpmfile.json

@@ -333,6 +333,11 @@
         "repo": "herumi/xbyak",
         "version": "v7.40.1"
     },
+    "zbic": {
+        "hash": "fbe2f37986377d7f0d96ae3224c80b5971df6e8b6961f68061f1975ebb2e8cb78f07b90f014b007be4023dbf5513581504e7f7d61a5237cb2a8a7a61ae11e482",
+        "repo": "kinnay/zbic",
+        "version": "11b08f2712264bbed731545085cbd9702096ceb7"
+    },
     "zlib": {
         "hash": "16fea4df307a68cf0035858abe2fd550250618a97590e202037acd18a666f57afc10f8836cbbd472d54a0e76539d0e558cb26f059d53de52ff90634bbf4f47d4",
         "min_version": "1.2",

externals/CMakeLists.txt

@@ -48,6 +48,11 @@ if (NOT TARGET stb::headers)
     add_library(stb::headers ALIAS stb)
 endif()
 
+AddJsonPackage(NAME zbic DOWNLOAD_ONLY)
+set(ZBIC_INCLUDE_DIR
+    "${zbic_SOURCE_DIR}/src"
+    PARENT_SCOPE)
+
 # ItaniumDemangle (Windows only)
 if (WIN32 AND NOT TARGET LLVM::Demangle)
     add_library(demangle demangle/ItaniumDemangle.cpp)

src/common/CMakeLists.txt

@@ -137,6 +137,8 @@ add_library(
     uuid.cpp
     uuid.h
     vector_math.h
+    zbic_compression.cpp
+    zbic_compression.h
     zstd_compression.cpp
     zstd_compression.h
     fs/ryujinx_compat.h fs/ryujinx_compat.cpp
@@ -147,6 +149,10 @@ add_library(
     net/net.h net/net.cpp
     container/unordered_map.h container/unordered_set.h)
 
+set_source_files_properties(zbic_compression.cpp PROPERTIES
+    INCLUDE_DIRECTORIES "${ZBIC_INCLUDE_DIR}"
+    COMPILE_OPTIONS "$<$<CXX_COMPILER_ID:Clang,GNU>:-Wno-unused-function;-Wno-missing-declarations;-Wno-shadow>")
+
 if(WIN32)
     target_sources(common PRIVATE windows/timer_resolution.cpp
         windows/timer_resolution.h)

src/common/zbic_compression.cpp

@@ -0,0 +1,46 @@
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include <cstring>
+
+#include "common/zbic_compression.h"
+
+#define ZSTD_ZBIC_SUPPORT 1
+#define ZSTDLIB_VISIBLE static
+#define ZSTDLIB_HIDDEN static
+#define ZSTDERRORLIB_VISIBLE static
+#define ZSTDERRORLIB_HIDDEN static
+#undef ZSTD_MULTITHREAD
+
+#if defined(__ANDROID__)
+#undef _GNU_SOURCE
+#endif
+
+#include "zstd.h"
+#define g_ZSTD_threading_useless_symbol g_ZSTD_zbic_threading_useless_symbol
+#include "zstd.c"
+#undef g_ZSTD_threading_useless_symbol
+
+namespace Common::Compression {
+
+bool IsZBIC(std::span<const u8> src) {
+    if (src.size() < sizeof(u32)) {
+        return false;
+    }
+    u32 magic = 0;
+    std::memcpy(&magic, src.data(), sizeof(u32));
+    return magic == ZSTD_MAGICNUMBER; // 0x4349425A ("ZBIC")
+}
+
+int DecompressDataZBIC(std::span<u8> dst, std::span<const u8> src) {
+    if (dst.empty() || src.empty()) {
+        return -1;
+    }
+    const size_t res = ZSTD_decompress(dst.data(), dst.size(), src.data(), src.size());
+    if (ZSTD_isError(res)) {
+        return -1;
+    }
+    return static_cast<int>(res);
+}
+
+} // namespace Common::Compression

src/common/zbic_compression.h

@@ -0,0 +1,15 @@
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#pragma once
+
+#include <span>
+#include "common/common_types.h"
+
+namespace Common::Compression {
+
+[[nodiscard]] bool IsZBIC(std::span<const u8> src);
+
+[[nodiscard]] int DecompressDataZBIC(std::span<u8> dst, std::span<const u8> src);
+
+} // namespace Common::Compression

src/core/loader/nso.cpp

@@ -7,12 +7,14 @@
 #include <algorithm>
 #include <cinttypes>
 #include <cstring>
+#include <span>
 #include <vector>
 
 #include "common/common_funcs.h"
 #include "common/hex_util.h"
 #include "common/logging.h"
 #include "common/lz4_compression.h"
+#include "common/zbic_compression.h"
 #include "common/settings.h"
 #include "common/swap.h"
 #include "core/core.h"
@@ -104,11 +106,36 @@ std::optional<VAddr> AppLoader_NSO::LoadModule(Kernel::KProcess& process, Core::
         for (std::size_t i = 0; i < nso_header.segments.size(); ++i) {
             nso_file.Read(compressed_data.data(), nso_header.segments_compressed_size[i], nso_header.segments[i].offset);
             if (nso_header.IsSegmentCompressed(i)) {
-                int r = Common::Compression::DecompressDataLZ4(decompressed_size.data(), nso_header.segments[i].size, compressed_data.data(), nso_header.segments_compressed_size[i]);
-                ASSERT(r == int(nso_header.segments[i].size));
-                std::memcpy(codeset.memory.data() + module_start + nso_header.segments[i].location, decompressed_size.data(), nso_header.segments[i].size);
+                if (nso_header.IsZBICCompressed()) {
+                    // ZBIC compression
+                    const int r = Common::Compression::DecompressDataZBIC(
+                        std::span<u8>{decompressed_size}.first(nso_header.segments[i].size),
+                        std::span<const u8>{compressed_data}.first(nso_header.segments_compressed_size[i])
+                    );
+                    ASSERT(r > 0);
+                } else {
+                    // LZ4 compression
+                    int r = Common::Compression::DecompressDataLZ4(
+                        decompressed_size.data(),
+                        nso_header.segments[i].size,
+                        compressed_data.data(),
+                        nso_header.segments_compressed_size[i]
+                    );
+                    ASSERT(r == int(nso_header.segments[i].size));
+                }
+
+                std::memcpy(
+                    codeset.memory.data() + module_start + nso_header.segments[i].location,
+                    decompressed_size.data(),
+                    nso_header.segments[i].size
+                );
             } else {
-                std::memcpy(codeset.memory.data() + module_start + nso_header.segments[i].location, compressed_data.data(), nso_header.segments[i].size);
+                // Not compressed
+                std::memcpy(
+                    codeset.memory.data() + module_start + nso_header.segments[i].location,
+                    compressed_data.data(),
+                    nso_header.segments[i].size
+                );
             }
             codeset.segments[i].addr = module_start + nso_header.segments[i].location;
             codeset.segments[i].offset = module_start + nso_header.segments[i].location;

src/core/loader/nso.h

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // SPDX-FileCopyrightText: Copyright 2018 yuzu Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -58,6 +61,9 @@ struct NSOHeader {
     std::array<SHA256Hash, 3> segment_hashes;
 
     bool IsSegmentCompressed(size_t segment_num) const;
+    bool IsZBICCompressed() const {
+        return ((flags >> 7) & 1) != 0;
+    }
 };
 static_assert(sizeof(NSOHeader) == 0x100, "NSOHeader has incorrect size.");
 static_assert(std::is_trivially_copyable_v<NSOHeader>, "NSOHeader must be trivially copyable.");