[loader] Preserve nxlink argv markers

src/core/CMakeLists.txt

@@ -1139,6 +1139,8 @@ add_library(core STATIC
     launch_timestamp_cache.h
     loader/deconstructed_rom_directory.cpp
     loader/deconstructed_rom_directory.h
+    loader/homebrew_nxlink.cpp
+    loader/homebrew_nxlink.h
     loader/kip.cpp
     loader/kip.h
     loader/loader.cpp

src/core/hle/kernel/k_process.cpp

@@ -214,6 +214,7 @@ Result KProcess::Initialize(KernelCore& kernel, const Svc::CreateProcessParamete
     m_homebrew_next_load_path_addr = 0;
     m_homebrew_next_load_argv_addr = 0;
     m_is_homebrew_in_place_next_load = false;
+    m_has_homebrew_nxlink_argv_marker = false;
     m_code_size = params.code_num_pages * PageSize;
     m_is_application = True(params.flags & Svc::CreateProcessFlag::IsApplication);
 

src/core/hle/kernel/k_process.h

@@ -6,7 +6,9 @@
 
 #pragma once
 
+#include <array>
 #include <map>
+#include <string_view>
 
 #include "core/arm/arm_interface.h"
 #include "core/file_sys/program_metadata.h"
@@ -90,6 +92,7 @@ private:
     KProcessAddress m_process_handle_addr{};
     KProcessAddress m_homebrew_next_load_path_addr{};
     KProcessAddress m_homebrew_next_load_argv_addr{};
+    std::array<char, 16> m_homebrew_nxlink_argv_marker{};
     KHandleTable m_handle_table;
     KProcessAddress m_plr_address{};
     ThreadList m_thread_list{};
@@ -144,6 +147,7 @@ private:
     bool m_is_immortal : 1 = false;
     bool m_is_handle_table_initialized : 1 = false;
     bool m_is_homebrew_in_place_next_load : 1 = false;
+    bool m_has_homebrew_nxlink_argv_marker : 1 = false;
 
 private:
     Result StartTermination(KernelCore& kernel);
@@ -246,6 +250,24 @@ public:
     void SetHomebrewInPlaceNextLoad(bool enabled) {
         m_is_homebrew_in_place_next_load = enabled;
     }
+    void SetHomebrewNxlinkArgvMarker(std::string_view marker) {
+        if (marker.size() != m_homebrew_nxlink_argv_marker.size()) {
+            m_has_homebrew_nxlink_argv_marker = false;
+            return;
+        }
+
+        marker.copy(m_homebrew_nxlink_argv_marker.data(), m_homebrew_nxlink_argv_marker.size());
+        m_has_homebrew_nxlink_argv_marker = true;
+    }
+    void ClearHomebrewNxlinkArgvMarker() {
+        m_has_homebrew_nxlink_argv_marker = false;
+    }
+    std::string_view GetHomebrewNxlinkArgvMarker() const {
+        if (!m_has_homebrew_nxlink_argv_marker) {
+            return {};
+        }
+        return {m_homebrew_nxlink_argv_marker.data(), m_homebrew_nxlink_argv_marker.size()};
+    }
     bool IsHomebrewInPlaceNextLoad() const {
         return m_is_homebrew_in_place_next_load;
     }

src/core/loader/homebrew_nxlink.cpp

@@ -0,0 +1,109 @@
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include "core/loader/homebrew_nxlink.h"
+
+#include <cctype>
+
+namespace Loader::HomebrewNxlink {
+namespace {
+
+std::optional<std::string> GetLastArgvToken(std::string_view argv_string) {
+    while (!argv_string.empty() && argv_string.back() == '\0') {
+        argv_string.remove_suffix(1);
+    }
+
+    std::optional<std::string_view> last_token;
+    bool in_token = false;
+    bool quoted = false;
+    size_t token_begin = 0;
+    size_t token_size = 0;
+
+    for (size_t i = 0; i <= argv_string.size(); i++) {
+        const char c = i < argv_string.size() ? argv_string[i] : '\0';
+
+        if (!in_token) {
+            if (c == '\0' || std::isspace(static_cast<unsigned char>(c))) {
+                continue;
+            }
+
+            in_token = true;
+            token_size = 0;
+            if (c == '"') {
+                quoted = true;
+                token_begin = i + 1;
+            } else {
+                quoted = false;
+                token_begin = i;
+                token_size = 1;
+            }
+            continue;
+        }
+
+        const bool token_end =
+            quoted ? c == '"' || c == '\0'
+                   : c == '\0' || std::isspace(static_cast<unsigned char>(c));
+        if (token_end) {
+            if (token_size != 0) {
+                last_token = argv_string.substr(token_begin, token_size);
+            }
+            in_token = false;
+            quoted = false;
+            token_size = 0;
+            continue;
+        }
+
+        token_size++;
+    }
+
+    if (!last_token) {
+        return std::nullopt;
+    }
+    return std::string{*last_token};
+}
+
+void AppendArgvToken(std::string& argv_string, std::string_view token) {
+    while (!argv_string.empty() && argv_string.back() == '\0') {
+        argv_string.pop_back();
+    }
+    if (!argv_string.empty()) {
+        argv_string.push_back(' ');
+    }
+    argv_string.append(token);
+}
+
+} // namespace
+
+bool IsArgvMarker(std::string_view token) {
+    if (token.size() != ArgvMarkerSize || token.substr(8) != ArgvMarkerSuffix) {
+        return false;
+    }
+
+    for (size_t i = 0; i < 8; i++) {
+        if (!std::isxdigit(static_cast<unsigned char>(token[i]))) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+std::optional<std::string> GetArgvMarker(std::string_view argv_string) {
+    auto last_token = GetLastArgvToken(argv_string);
+    if (!last_token || !IsArgvMarker(*last_token)) {
+        return std::nullopt;
+    }
+    return last_token;
+}
+
+std::optional<std::string> PrepareArgv(std::string& argv_string,
+                                       std::string_view inherited_marker) {
+    auto marker = GetArgvMarker(argv_string);
+    if (!marker && IsArgvMarker(inherited_marker)) {
+        AppendArgvToken(argv_string, inherited_marker);
+        marker = std::string{inherited_marker};
+    }
+    return marker;
+}
+
+} // namespace Loader::HomebrewNxlink

src/core/loader/homebrew_nxlink.h

@@ -0,0 +1,23 @@
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#pragma once
+
+#include <cstddef>
+#include <optional>
+#include <string>
+#include <string_view>
+
+namespace Loader::HomebrewNxlink {
+
+constexpr size_t ArgvMarkerSize = 16;
+constexpr std::string_view ArgvMarkerSuffix = "_NXLINK_";
+
+// This module handles only the libnx argv marker. Client stream handling should be an
+// explicit byte-sink API; the marker alone must not imply logging.
+bool IsArgvMarker(std::string_view token);
+std::optional<std::string> GetArgvMarker(std::string_view argv_string);
+std::optional<std::string> PrepareArgv(std::string& argv_string,
+                                       std::string_view inherited_marker);
+
+} // namespace Loader::HomebrewNxlink

src/core/loader/nro.cpp

@@ -33,6 +33,7 @@
 #include "core/hle/kernel/k_process.h"
 #include "core/hle/kernel/k_thread.h"
 #include "core/hle/service/filesystem/filesystem.h"
+#include "core/loader/homebrew_nxlink.h"
 #include "core/loader/nro.h"
 #include "core/memory.h"
 
@@ -319,6 +320,7 @@ struct HomebrewNroImage {
     size_t image_size{};
     size_t args_offset{};
     std::optional<size_t> exit_process_offset;
+    std::optional<std::string> nxlink_argv_marker;
     std::string argv_string;
 };
 
@@ -340,7 +342,8 @@ static void SetHomebrewConfigPointers(Kernel::KProcess& process, u64 config_addr
 static std::optional<HomebrewNroImage> BuildHomebrewNroImage(const std::vector<u8>& data,
                                                              std::string nro_path,
                                                              std::string file_name,
-                                                             std::string launch_argv) {
+                                                             std::string launch_argv,
+                                                             std::string_view inherited_marker) {
     if (data.size() < sizeof(NroHeader)) {
         return std::nullopt;
     }
@@ -385,6 +388,7 @@ static std::optional<HomebrewNroImage> BuildHomebrewNroImage(const std::vector<u
     } else {
         image.argv_string = QuoteHomebrewArgvComponent(argv0);
     }
+    image.nxlink_argv_marker = HomebrewNxlink::PrepareArgv(image.argv_string, inherited_marker);
     if (image.argv_string.empty() || image.argv_string.back() != '\0') {
         image.argv_string.push_back('\0');
     }
@@ -447,8 +451,8 @@ bool LoadNroInPlace(Core::System& system, Kernel::KProcess& process, Kernel::KTh
         return false;
     }
 
-    auto image =
-        BuildHomebrewNroImage(nro_file->ReadAllBytes(), nro_path, nro_file->GetName(), launch_argv);
+    auto image = BuildHomebrewNroImage(nro_file->ReadAllBytes(), nro_path, nro_file->GetName(),
+                                       launch_argv, process.GetHomebrewNxlinkArgvMarker());
     if (!image) {
         LOG_WARNING(Loader, "NextLoad: in-place handoff failed because '{}' is invalid",
                     nro_path);
@@ -538,6 +542,11 @@ bool LoadNroInPlace(Core::System& system, Kernel::KProcess& process, Kernel::KTh
     process.SetArgReturnAddress(Kernel::KProcessAddress{
         image->exit_process_offset ? base + *image->exit_process_offset : 0});
     SetHomebrewConfigPointers(process, config_addr, next_load_path_addr, next_load_argv_addr);
+    if (image->nxlink_argv_marker) {
+        process.SetHomebrewNxlinkArgvMarker(*image->nxlink_argv_marker);
+    } else {
+        process.ClearHomebrewNxlinkArgvMarker();
+    }
     system.GetFileSystemController().RegisterProcess(
         process.GetProcessId(), program_id,
         std::make_unique<FileSys::RomFSFactory>(loader, system.GetContentProvider(),
@@ -619,6 +628,7 @@ static bool LoadNroImpl(Core::System& system, Kernel::KProcess& process,
         argv_string.push_back(' ');
         argv_string += program_args;
     }
+    const auto nxlink_argv_marker = HomebrewNxlink::PrepareArgv(argv_string, {});
     if (argv_string.empty() || argv_string.back() != '\0') {
         argv_string.push_back('\0');
     }
@@ -712,6 +722,11 @@ static bool LoadNroImpl(Core::System& system, Kernel::KProcess& process,
     codeset.memory = std::move(program_image);
     process.LoadModule(system.Kernel(), std::move(codeset), process.GetEntryPoint());
     process.SetHomebrewInPlaceNextLoad(false);
+    if (nxlink_argv_marker) {
+        process.SetHomebrewNxlinkArgvMarker(*nxlink_argv_marker);
+    } else {
+        process.ClearHomebrewNxlinkArgvMarker();
+    }
     {
         const u64 base = GetInteger(process.GetEntryPoint());
         const u64 config_addr = base + args_offset_in_image;