Merge pull request #2975 from shinyquagsire23/archive-ncch-container-and-override

file_sys/archive_ncch: use NCCHs/.apps instead of .romfs files, NCCH section override

src/core/CMakeLists.txt

@@ -29,6 +29,7 @@ set(SRCS
             file_sys/ncch_container.cpp
             file_sys/path_parser.cpp
             file_sys/savedata_archive.cpp
+            file_sys/title_metadata.cpp
             frontend/camera/blank_camera.cpp
             frontend/camera/factory.cpp
             frontend/camera/interface.cpp

src/core/file_sys/archive_ncch.cpp

@@ -13,7 +13,10 @@
 #include "core/file_sys/archive_ncch.h"
 #include "core/file_sys/errors.h"
 #include "core/file_sys/ivfc_archive.h"
+#include "core/file_sys/ncch_container.h"
+#include "core/file_sys/title_metadata.h"
 #include "core/hle/service/fs/archive.h"
+#include "core/loader/loader.h"
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 // FileSys namespace
@@ -25,8 +28,18 @@ static std::string GetNCCHContainerPath(const std::string& nand_directory) {
 }
 
 static std::string GetNCCHPath(const std::string& mount_point, u32 high, u32 low) {
-    return Common::StringFromFormat("%s%08x/%08x/content/00000000.app.romfs", mount_point.c_str(),
+    u32 content_id = 0;
-                                    high, low);
+
+    // TODO(shinyquagsire23): Title database should be doing this path lookup
+    std::string content_path =
+        Common::StringFromFormat("%s%08x/%08x/content/", mount_point.c_str(), high, low);
+    std::string tmd_path = content_path + "00000000.tmd";
+    TitleMetadata tmd(tmd_path);
+    if (tmd.Load() == Loader::ResultStatus::Success) {
+        content_id = tmd.GetBootContentID();
+    }
+
+    return Common::StringFromFormat("%s%08x.app", content_path.c_str(), content_id);
 }
 
 ArchiveFactory_NCCH::ArchiveFactory_NCCH(const std::string& nand_directory)
@@ -38,9 +51,14 @@ ResultVal<std::unique_ptr<ArchiveBackend>> ArchiveFactory_NCCH::Open(const Path&
     u32 high = data[1];
     u32 low = data[0];
     std::string file_path = GetNCCHPath(mount_point, high, low);
-    auto file = std::make_shared<FileUtil::IOFile>(file_path, "rb");
 
-    if (!file->IsOpen()) {
+    std::shared_ptr<FileUtil::IOFile> romfs_file;
+    u64 romfs_offset = 0;
+    u64 romfs_size = 0;
+    auto ncch_container = NCCHContainer(file_path);
+
+    if (ncch_container.ReadRomFS(romfs_file, romfs_offset, romfs_size) !=
+        Loader::ResultStatus::Success) {
         // High Title ID of the archive: The category (https://3dbrew.org/wiki/Title_list).
         constexpr u32 shared_data_archive = 0x0004009B;
         constexpr u32 system_data_archive = 0x000400DB;
@@ -74,9 +92,8 @@ ResultVal<std::unique_ptr<ArchiveBackend>> ArchiveFactory_NCCH::Open(const Path&
         }
         return ERROR_NOT_FOUND;
     }
-    auto size = file->GetSize();
 
-    auto archive = std::make_unique<IVFCArchive>(file, 0, size);
+    auto archive = std::make_unique<IVFCArchive>(romfs_file, romfs_offset, romfs_size);
     return MakeResult<std::unique_ptr<ArchiveBackend>>(std::move(archive));
 }
 

src/core/file_sys/ncch_container.cpp

@@ -116,6 +116,7 @@ Loader::ResultStatus NCCHContainer::Load() {
     if (is_loaded)
         return Loader::ResultStatus::Success;
 
+    if (file.IsOpen()) {
         // Reset read pointer in case this file has been read before.
         file.Seek(0, SEEK_SET);
 
@@ -134,9 +135,12 @@ Loader::ResultStatus NCCHContainer::Load() {
         if (Loader::MakeMagic('N', 'C', 'C', 'H') != ncch_header.magic)
             return Loader::ResultStatus::ErrorInvalidFormat;
 
+        has_header = true;
+
         // System archives and DLC don't have an extended header but have RomFS
         if (ncch_header.extended_header_size) {
-        if (file.ReadBytes(&exheader_header, sizeof(ExHeader_Header)) != sizeof(ExHeader_Header))
+            if (file.ReadBytes(&exheader_header, sizeof(ExHeader_Header)) !=
+                sizeof(ExHeader_Header))
                 return Loader::ResultStatus::Error;
 
             is_compressed = (exheader_header.codeset_info.flags.flag & 1) == 1;
@@ -149,8 +153,10 @@ Loader::ResultStatus NCCHContainer::Load() {
             u8 resource_limit_category =
                 exheader_header.arm11_system_local_caps.resource_limit_category;
 
-        LOG_DEBUG(Service_FS, "Name:                        %s", exheader_header.codeset_info.name);
+            LOG_DEBUG(Service_FS, "Name:                        %s",
-        LOG_DEBUG(Service_FS, "Program ID:                  %016" PRIX64, ncch_header.program_id);
+                      exheader_header.codeset_info.name);
+            LOG_DEBUG(Service_FS, "Program ID:                  %016" PRIX64,
+                      ncch_header.program_id);
             LOG_DEBUG(Service_FS, "Code compressed:             %s", is_compressed ? "yes" : "no");
             LOG_DEBUG(Service_FS, "Entry point:                 0x%08X", entry_point);
             LOG_DEBUG(Service_FS, "Code size:                   0x%08X", code_size);
@@ -163,7 +169,8 @@ Loader::ResultStatus NCCHContainer::Load() {
                       static_cast<int>(exheader_header.arm11_system_local_caps.system_mode));
 
             if (exheader_header.system_info.jump_id != ncch_header.program_id) {
-            LOG_ERROR(Service_FS, "ExHeader Program ID mismatch: the ROM is probably encrypted.");
+                LOG_ERROR(Service_FS,
+                          "ExHeader Program ID mismatch: the ROM is probably encrypted.");
                 return Loader::ResultStatus::ErrorEncrypted;
             }
 
@@ -182,26 +189,70 @@ Loader::ResultStatus NCCHContainer::Load() {
             if (file.ReadBytes(&exefs_header, sizeof(ExeFs_Header)) != sizeof(ExeFs_Header))
                 return Loader::ResultStatus::Error;
 
+            exefs_file = FileUtil::IOFile(filepath, "rb");
             has_exefs = true;
         }
 
         if (ncch_header.romfs_offset != 0 && ncch_header.romfs_size != 0)
             has_romfs = true;
+    }
+
+    LoadOverrides();
+
+    // We need at least one of these or overrides, practically
+    if (!(has_exefs || has_romfs || is_tainted))
+        return Loader::ResultStatus::Error;
 
     is_loaded = true;
     return Loader::ResultStatus::Success;
 }
 
-Loader::ResultStatus NCCHContainer::LoadSectionExeFS(const char* name, std::vector<u8>& buffer) {
+Loader::ResultStatus NCCHContainer::LoadOverrides() {
-    if (!file.IsOpen())
+    // Check for split-off files, mark the archive as tainted if we will use them
-        return Loader::ResultStatus::Error;
+    std::string romfs_override = filepath + ".romfs";
+    if (FileUtil::Exists(romfs_override)) {
+        is_tainted = true;
+    }
 
+    // If we have a split-off exefs file/folder, it takes priority
+    std::string exefs_override = filepath + ".exefs";
+    std::string exefsdir_override = filepath + ".exefsdir/";
+    if (FileUtil::Exists(exefs_override)) {
+        exefs_file = FileUtil::IOFile(exefs_override, "rb");
+
+        if (exefs_file.ReadBytes(&exefs_header, sizeof(ExeFs_Header)) == sizeof(ExeFs_Header)) {
+            LOG_DEBUG(Service_FS, "Loading ExeFS section from %s", exefs_override.c_str());
+            exefs_offset = 0;
+            is_tainted = true;
+            has_exefs = true;
+        } else {
+            exefs_file = FileUtil::IOFile(filepath, "rb");
+        }
+    } else if (FileUtil::Exists(exefsdir_override) && FileUtil::IsDirectory(exefsdir_override)) {
+        is_tainted = true;
+    }
+
+    if (is_tainted)
+        LOG_WARNING(Service_FS,
+                    "Loaded NCCH %s is tainted, application behavior may not be as expected!",
+                    filepath.c_str());
+
+    return Loader::ResultStatus::Success;
+}
+
+Loader::ResultStatus NCCHContainer::LoadSectionExeFS(const char* name, std::vector<u8>& buffer) {
     Loader::ResultStatus result = Load();
     if (result != Loader::ResultStatus::Success)
         return result;
 
-    if (!has_exefs)
+    // Check if we have files that can drop-in and replace
-        return Loader::ResultStatus::ErrorNotUsed;
+    result = LoadOverrideExeFSSection(name, buffer);
+    if (result == Loader::ResultStatus::Success || !has_exefs)
+        return result;
+
+    // If we don't have any separate files, we'll need a full ExeFS
+    if (!exefs_file.IsOpen())
+        return Loader::ResultStatus::Error;
 
     LOG_DEBUG(Service_FS, "%d sections:", kMaxSections);
     // Iterate through the ExeFs archive until we find a section with the specified name...
@@ -215,7 +266,7 @@ Loader::ResultStatus NCCHContainer::LoadSectionExeFS(const char* name, std::vect
 
             s64 section_offset =
                 (section.offset + exefs_offset + sizeof(ExeFs_Header) + ncch_offset);
-            file.Seek(section_offset, SEEK_SET);
+            exefs_file.Seek(section_offset, SEEK_SET);
 
             if (strcmp(section.name, ".code") == 0 && is_compressed) {
                 // Section is compressed, read compressed .code section...
@@ -226,7 +277,7 @@ Loader::ResultStatus NCCHContainer::LoadSectionExeFS(const char* name, std::vect
                     return Loader::ResultStatus::ErrorMemoryAllocationFailed;
                 }
 
-                if (file.ReadBytes(&temp_buffer[0], section.size) != section.size)
+                if (exefs_file.ReadBytes(&temp_buffer[0], section.size) != section.size)
                     return Loader::ResultStatus::Error;
 
                 // Decompress .code section...
@@ -237,7 +288,7 @@ Loader::ResultStatus NCCHContainer::LoadSectionExeFS(const char* name, std::vect
             } else {
                 // Section is uncompressed...
                 buffer.resize(section.size);
-                if (file.ReadBytes(&buffer[0], section.size) != section.size)
+                if (exefs_file.ReadBytes(&buffer[0], section.size) != section.size)
                     return Loader::ResultStatus::Error;
             }
             return Loader::ResultStatus::Success;
@@ -246,20 +297,56 @@ Loader::ResultStatus NCCHContainer::LoadSectionExeFS(const char* name, std::vect
     return Loader::ResultStatus::ErrorNotUsed;
 }
 
-Loader::ResultStatus NCCHContainer::ReadRomFS(std::shared_ptr<FileUtil::IOFile>& romfs_file,
+Loader::ResultStatus NCCHContainer::LoadOverrideExeFSSection(const char* name,
-                                              u64& offset, u64& size) {
+                                                             std::vector<u8>& buffer) {
-    if (!file.IsOpen())
+    std::string override_name;
+
+    // Map our section name to the extracted equivalent
+    if (!strcmp(name, ".code"))
+        override_name = "code.bin";
+    else if (!strcmp(name, "icon"))
+        override_name = "code.bin";
+    else if (!strcmp(name, "banner"))
+        override_name = "banner.bnr";
+    else if (!strcmp(name, "logo"))
+        override_name = "logo.bcma.lz";
+    else
         return Loader::ResultStatus::Error;
 
+    std::string section_override = filepath + ".exefsdir/" + override_name;
+    FileUtil::IOFile section_file(section_override, "rb");
+
+    if (section_file.IsOpen()) {
+        auto section_size = section_file.GetSize();
+        buffer.resize(section_size);
+
+        section_file.Seek(0, SEEK_SET);
+        if (section_file.ReadBytes(&buffer[0], section_size) == section_size) {
+            LOG_WARNING(Service_FS, "File %s overriding built-in ExeFS file",
+                        section_override.c_str());
+            return Loader::ResultStatus::Success;
+        }
+    }
+    return Loader::ResultStatus::ErrorNotUsed;
+}
+
+Loader::ResultStatus NCCHContainer::ReadRomFS(std::shared_ptr<FileUtil::IOFile>& romfs_file,
+                                              u64& offset, u64& size) {
     Loader::ResultStatus result = Load();
     if (result != Loader::ResultStatus::Success)
         return result;
 
+    if (ReadOverrideRomFS(romfs_file, offset, size) == Loader::ResultStatus::Success)
+        return Loader::ResultStatus::Success;
+
     if (!has_romfs) {
         LOG_DEBUG(Service_FS, "RomFS requested from NCCH which has no RomFS");
         return Loader::ResultStatus::ErrorNotUsed;
     }
 
+    if (!file.IsOpen())
+        return Loader::ResultStatus::Error;
+
     u32 romfs_offset = ncch_offset + (ncch_header.romfs_offset * kBlockSize) + 0x1000;
     u32 romfs_size = (ncch_header.romfs_size * kBlockSize) - 0x1000;
 
@@ -280,11 +367,31 @@ Loader::ResultStatus NCCHContainer::ReadRomFS(std::shared_ptr<FileUtil::IOFile>&
     return Loader::ResultStatus::Success;
 }
 
+Loader::ResultStatus NCCHContainer::ReadOverrideRomFS(std::shared_ptr<FileUtil::IOFile>& romfs_file,
+                                                      u64& offset, u64& size) {
+    // Check for RomFS overrides
+    std::string split_filepath = filepath + ".romfs";
+    if (FileUtil::Exists(split_filepath)) {
+        romfs_file = std::make_shared<FileUtil::IOFile>(split_filepath, "rb");
+        if (romfs_file->IsOpen()) {
+            LOG_WARNING(Service_FS, "File %s overriding built-in RomFS", split_filepath.c_str());
+            offset = 0;
+            size = romfs_file->GetSize();
+            return Loader::ResultStatus::Success;
+        }
+    }
+
+    return Loader::ResultStatus::ErrorNotUsed;
+}
+
 Loader::ResultStatus NCCHContainer::ReadProgramId(u64_le& program_id) {
     Loader::ResultStatus result = Load();
     if (result != Loader::ResultStatus::Success)
         return result;
 
+    if (!has_header)
+        return Loader::ResultStatus::ErrorNotUsed;
+
     program_id = ncch_header.program_id;
     return Loader::ResultStatus::Success;
 }

src/core/file_sys/ncch_container.h

@@ -179,6 +179,13 @@ public:
      */
     Loader::ResultStatus Load();
 
+    /**
+     * Attempt to find overridden sections for the NCCH and mark the container as tainted
+     * if any are found.
+     * @return ResultStatus result of function
+     */
+    Loader::ResultStatus LoadOverrides();
+
     /**
      * Reads an application ExeFS section of an NCCH file (e.g. .code, .logo, etc.)
      * @param name Name of section to read out of NCCH file
@@ -187,6 +194,15 @@ public:
      */
     Loader::ResultStatus LoadSectionExeFS(const char* name, std::vector<u8>& buffer);
 
+    /**
+     * Reads an application ExeFS section from external files instead of an NCCH file,
+     * (e.g. code.bin, logo.bcma.lz, icon.icn, banner.bnr)
+     * @param name Name of section to read from external files
+     * @param buffer Vector to read data into
+     * @return ResultStatus result of function
+     */
+    Loader::ResultStatus LoadOverrideExeFSSection(const char* name, std::vector<u8>& buffer);
+
     /**
      * Get the RomFS of the NCCH container
      * Since the RomFS can be huge, we return a file reference instead of copying to a buffer
@@ -198,6 +214,17 @@ public:
     Loader::ResultStatus ReadRomFS(std::shared_ptr<FileUtil::IOFile>& romfs_file, u64& offset,
                                    u64& size);
 
+    /**
+    * Get the override RomFS of the NCCH container
+    * Since the RomFS can be huge, we return a file reference instead of copying to a buffer
+    * @param romfs_file The file containing the RomFS
+    * @param offset The offset the romfs begins on
+    * @param size The size of the romfs
+    * @return ResultStatus result of function
+    */
+    Loader::ResultStatus ReadOverrideRomFS(std::shared_ptr<FileUtil::IOFile>& romfs_file,
+                                           u64& offset, u64& size);
+
     /**
      * Get the Program ID of the NCCH container
      * @return ResultStatus result of function
@@ -227,10 +254,12 @@ public:
     ExHeader_Header exheader_header;
 
 private:
+    bool has_header = false;
     bool has_exheader = false;
     bool has_exefs = false;
     bool has_romfs = false;
 
+    bool is_tainted = false; // Are there parts of this container being overridden?
     bool is_loaded = false;
     bool is_compressed = false;
 
@@ -239,6 +268,7 @@ private:
 
     std::string filepath;
     FileUtil::IOFile file;
+    FileUtil::IOFile exefs_file;
 };
 
 } // namespace FileSys

src/core/file_sys/title_metadata.cpp

@@ -0,0 +1,212 @@
+// Copyright 2017 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include <cinttypes>
+#include <cryptopp/sha.h>
+#include "common/alignment.h"
+#include "common/file_util.h"
+#include "common/logging/log.h"
+#include "core/file_sys/title_metadata.h"
+#include "core/loader/loader.h"
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+// FileSys namespace
+
+namespace FileSys {
+
+static u32 GetSignatureSize(u32 signature_type) {
+    switch (signature_type) {
+    case Rsa4096Sha1:
+    case Rsa4096Sha256:
+        return 0x200;
+
+    case Rsa2048Sha1:
+    case Rsa2048Sha256:
+        return 0x100;
+
+    case EllipticSha1:
+    case EcdsaSha256:
+        return 0x3C;
+    }
+}
+
+Loader::ResultStatus TitleMetadata::Load() {
+    FileUtil::IOFile file(filepath, "rb");
+    if (!file.IsOpen())
+        return Loader::ResultStatus::Error;
+
+    if (!file.ReadBytes(&signature_type, sizeof(u32_be)))
+        return Loader::ResultStatus::Error;
+
+    // Signature lengths are variable, and the body follows the signature
+    u32 signature_size = GetSignatureSize(signature_type);
+
+    tmd_signature.resize(signature_size);
+    if (!file.ReadBytes(&tmd_signature[0], signature_size))
+        return Loader::ResultStatus::Error;
+
+    // The TMD body start position is rounded to the nearest 0x40 after the signature
+    size_t body_start = Common::AlignUp(signature_size + sizeof(u32), 0x40);
+    file.Seek(body_start, SEEK_SET);
+
+    // Read our TMD body, then load the amount of ContentChunks specified
+    if (file.ReadBytes(&tmd_body, sizeof(TitleMetadata::Body)) != sizeof(TitleMetadata::Body))
+        return Loader::ResultStatus::Error;
+
+    for (u16 i = 0; i < tmd_body.content_count; i++) {
+        ContentChunk chunk;
+        if (file.ReadBytes(&chunk, sizeof(ContentChunk)) == sizeof(ContentChunk)) {
+            tmd_chunks.push_back(chunk);
+        } else {
+            LOG_ERROR(Service_FS, "Malformed TMD %s, failed to load content chunk index %u!",
+                      filepath.c_str(), i);
+            return Loader::ResultStatus::ErrorInvalidFormat;
+        }
+    }
+
+    return Loader::ResultStatus::Success;
+}
+
+Loader::ResultStatus TitleMetadata::Save() {
+    FileUtil::IOFile file(filepath, "wb");
+    if (!file.IsOpen())
+        return Loader::ResultStatus::Error;
+
+    if (!file.WriteBytes(&signature_type, sizeof(u32_be)))
+        return Loader::ResultStatus::Error;
+
+    // Signature lengths are variable, and the body follows the signature
+    u32 signature_size = GetSignatureSize(signature_type);
+
+    if (!file.WriteBytes(tmd_signature.data(), signature_size))
+        return Loader::ResultStatus::Error;
+
+    // The TMD body start position is rounded to the nearest 0x40 after the signature
+    size_t body_start = Common::AlignUp(signature_size + sizeof(u32), 0x40);
+    file.Seek(body_start, SEEK_SET);
+
+    // Update our TMD body values and hashes
+    tmd_body.content_count = static_cast<u16>(tmd_chunks.size());
+
+    // TODO(shinyquagsire23): Do TMDs with more than one contentinfo exist?
+    // For now we'll just adjust the first index to hold all content chunks
+    // and ensure that no further content info data exists.
+    tmd_body.contentinfo = {};
+    tmd_body.contentinfo[0].index = 0;
+    tmd_body.contentinfo[0].command_count = static_cast<u16>(tmd_chunks.size());
+
+    CryptoPP::SHA256 chunk_hash;
+    for (u16 i = 0; i < tmd_body.content_count; i++) {
+        chunk_hash.Update(reinterpret_cast<u8*>(&tmd_chunks[i]), sizeof(ContentChunk));
+    }
+    chunk_hash.Final(tmd_body.contentinfo[0].hash.data());
+
+    CryptoPP::SHA256 contentinfo_hash;
+    for (size_t i = 0; i < tmd_body.contentinfo.size(); i++) {
+        chunk_hash.Update(reinterpret_cast<u8*>(&tmd_body.contentinfo[i]), sizeof(ContentInfo));
+    }
+    chunk_hash.Final(tmd_body.contentinfo_hash.data());
+
+    // Write our TMD body, then write each of our ContentChunks
+    if (file.WriteBytes(&tmd_body, sizeof(TitleMetadata::Body)) != sizeof(TitleMetadata::Body))
+        return Loader::ResultStatus::Error;
+
+    for (u16 i = 0; i < tmd_body.content_count; i++) {
+        ContentChunk chunk = tmd_chunks[i];
+        if (file.WriteBytes(&chunk, sizeof(ContentChunk)) != sizeof(ContentChunk))
+            return Loader::ResultStatus::Error;
+    }
+
+    return Loader::ResultStatus::Success;
+}
+
+u64 TitleMetadata::GetTitleID() const {
+    return tmd_body.title_id;
+}
+
+u32 TitleMetadata::GetTitleType() const {
+    return tmd_body.title_type;
+}
+
+u16 TitleMetadata::GetTitleVersion() const {
+    return tmd_body.title_version;
+}
+
+u64 TitleMetadata::GetSystemVersion() const {
+    return tmd_body.system_version;
+}
+
+size_t TitleMetadata::GetContentCount() const {
+    return tmd_chunks.size();
+}
+
+u32 TitleMetadata::GetBootContentID() const {
+    return tmd_chunks[TMDContentIndex::Main].id;
+}
+
+u32 TitleMetadata::GetManualContentID() const {
+    return tmd_chunks[TMDContentIndex::Manual].id;
+}
+
+u32 TitleMetadata::GetDLPContentID() const {
+    return tmd_chunks[TMDContentIndex::DLP].id;
+}
+
+void TitleMetadata::SetTitleID(u64 title_id) {
+    tmd_body.title_id = title_id;
+}
+
+void TitleMetadata::SetTitleType(u32 type) {
+    tmd_body.title_type = type;
+}
+
+void TitleMetadata::SetTitleVersion(u16 version) {
+    tmd_body.title_version = version;
+}
+
+void TitleMetadata::SetSystemVersion(u64 version) {
+    tmd_body.system_version = version;
+}
+
+void TitleMetadata::AddContentChunk(const ContentChunk& chunk) {
+    tmd_chunks.push_back(chunk);
+}
+
+void TitleMetadata::Print() const {
+    LOG_DEBUG(Service_FS, "%s - %u chunks", filepath.c_str(),
+              static_cast<u32>(tmd_body.content_count));
+
+    // Content info describes ranges of content chunks
+    LOG_DEBUG(Service_FS, "Content info:");
+    for (size_t i = 0; i < tmd_body.contentinfo.size(); i++) {
+        if (tmd_body.contentinfo[i].command_count == 0)
+            break;
+
+        LOG_DEBUG(Service_FS, "    Index %04X, Command Count %04X",
+                  static_cast<u32>(tmd_body.contentinfo[i].index),
+                  static_cast<u32>(tmd_body.contentinfo[i].command_count));
+    }
+
+    // For each content info, print their content chunk range
+    for (size_t i = 0; i < tmd_body.contentinfo.size(); i++) {
+        u16 index = static_cast<u16>(tmd_body.contentinfo[i].index);
+        u16 count = static_cast<u16>(tmd_body.contentinfo[i].command_count);
+
+        if (count == 0)
+            continue;
+
+        LOG_DEBUG(Service_FS, "Content chunks for content info index %zu:", i);
+        for (u16 j = index; j < index + count; j++) {
+            // Don't attempt to print content we don't have
+            if (j > tmd_body.content_count)
+                break;
+
+            const ContentChunk& chunk = tmd_chunks[j];
+            LOG_DEBUG(Service_FS, "    ID %08X, Index %04X, Type %04x, Size %016" PRIX64,
+                      static_cast<u32>(chunk.id), static_cast<u32>(chunk.index),
+                      static_cast<u32>(chunk.type), static_cast<u64>(chunk.size));
+        }
+    }
+}
+} // namespace FileSys

src/core/file_sys/title_metadata.h

@@ -0,0 +1,125 @@
+// Copyright 2017 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <string>
+#include <vector>
+#include "common/common_types.h"
+#include "common/swap.h"
+
+namespace Loader {
+enum class ResultStatus;
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+// FileSys namespace
+
+namespace FileSys {
+
+enum TMDSignatureType : u32 {
+    Rsa4096Sha1 = 0x10000,
+    Rsa2048Sha1 = 0x10001,
+    EllipticSha1 = 0x10002,
+    Rsa4096Sha256 = 0x10003,
+    Rsa2048Sha256 = 0x10004,
+    EcdsaSha256 = 0x10005
+};
+
+enum TMDContentTypeFlag : u16 {
+    Encrypted = 1 << 1,
+    Disc = 1 << 2,
+    CFM = 1 << 3,
+    Optional = 1 << 14,
+    Shared = 1 << 15
+};
+
+/**
+ * Helper which implements an interface to read and write Title Metadata (TMD) files.
+ * If a file path is provided and the file exists, it can be parsed and used, otherwise
+ * it must be created. The TMD file can then be interpreted, modified and/or saved.
+ */
+class TitleMetadata {
+public:
+    struct ContentChunk {
+        u32_be id;
+        u16_be index;
+        u16_be type;
+        u64_be size;
+        std::array<u8, 0x20> hash;
+    };
+
+    static_assert(sizeof(ContentChunk) == 0x30, "TMD ContentChunk structure size is wrong");
+
+    struct ContentInfo {
+        u16_be index;
+        u16_be command_count;
+        std::array<u8, 0x20> hash;
+    };
+
+    static_assert(sizeof(ContentInfo) == 0x24, "TMD ContentInfo structure size is wrong");
+
+#pragma pack(push, 1)
+
+    struct Body {
+        std::array<u8, 0x40> issuer;
+        u8 version;
+        u8 ca_crl_version;
+        u8 signer_crl_version;
+        u8 reserved;
+        u64_be system_version;
+        u64_be title_id;
+        u32_be title_type;
+        u16_be group_id;
+        u32_be savedata_size;
+        u32_be srl_private_savedata_size;
+        std::array<u8, 4> reserved_2;
+        u8 srl_flag;
+        std::array<u8, 0x31> reserved_3;
+        u32_be access_rights;
+        u16_be title_version;
+        u16_be content_count;
+        u16_be boot_content;
+        std::array<u8, 2> reserved_4;
+        std::array<u8, 0x20> contentinfo_hash;
+        std::array<ContentInfo, 64> contentinfo;
+    };
+
+    static_assert(sizeof(Body) == 0x9C4, "TMD body structure size is wrong");
+
+#pragma pack(pop)
+
+    explicit TitleMetadata(std::string& path) : filepath(std::move(path)) {}
+    Loader::ResultStatus Load();
+    Loader::ResultStatus Save();
+
+    u64 GetTitleID() const;
+    u32 GetTitleType() const;
+    u16 GetTitleVersion() const;
+    u64 GetSystemVersion() const;
+    size_t GetContentCount() const;
+    u32 GetBootContentID() const;
+    u32 GetManualContentID() const;
+    u32 GetDLPContentID() const;
+
+    void SetTitleID(u64 title_id);
+    void SetTitleType(u32 type);
+    void SetTitleVersion(u16 version);
+    void SetSystemVersion(u64 version);
+    void AddContentChunk(const ContentChunk& chunk);
+
+    void Print() const;
+
+private:
+    enum TMDContentIndex { Main = 0, Manual = 1, DLP = 2 };
+
+    Body tmd_body;
+    u32_be signature_type;
+    std::vector<u8> tmd_signature;
+    std::vector<ContentChunk> tmd_chunks;
+
+    std::string filepath;
+};
+
+} // namespace FileSys

src/core/loader/ncch.cpp

@@ -14,6 +14,7 @@
 #include "core/core.h"
 #include "core/file_sys/archive_selfncch.h"
 #include "core/file_sys/ncch_container.h"
+#include "core/file_sys/title_metadata.h"
 #include "core/hle/kernel/process.h"
 #include "core/hle/kernel/resource_limit.h"
 #include "core/hle/service/cfg/cfg.h"
@@ -49,9 +50,19 @@ static std::string GetUpdateNCCHPath(u64_le program_id) {
     u32 high = static_cast<u32>((program_id | UPDATE_MASK) >> 32);
     u32 low = static_cast<u32>((program_id | UPDATE_MASK) & 0xFFFFFFFF);
 
-    return Common::StringFromFormat("%sNintendo 3DS/%s/%s/title/%08x/%08x/content/00000000.app",
+    // TODO(shinyquagsire23): Title database should be doing this path lookup
-                                    FileUtil::GetUserPath(D_SDMC_IDX).c_str(), SYSTEM_ID, SDCARD_ID,
+    std::string content_path = Common::StringFromFormat(
-                                    high, low);
+        "%sNintendo 3DS/%s/%s/title/%08x/%08x/content/", FileUtil::GetUserPath(D_SDMC_IDX).c_str(),
+        SYSTEM_ID, SDCARD_ID, high, low);
+    std::string tmd_path = content_path + "00000000.tmd";
+
+    u32 content_id = 0;
+    FileSys::TitleMetadata tmd(tmd_path);
+    if (tmd.Load() == ResultStatus::Success) {
+        content_id = tmd.GetBootContentID();
+    }
+
+    return Common::StringFromFormat("%s%08x.app", content_path.c_str(), content_id);
 }
 
 std::pair<boost::optional<u32>, ResultStatus> AppLoader_NCCH::LoadKernelSystemMode() {