feat(libSceDiscMap): report no disc bitmap from the two disc map queries

Until Dawn (CUSA02636) bundles a libSceFios2.prx that imports two
libSceDiscMap functions, sceDiscMapIsRequestOnHDD (lbQKqsERhtE) and
ioKMruft1ek, and no host library exported them.

Both now return SCE_DISC_MAP_ERROR_NO_BITMAP_INFO (0x81100004) and
write nothing, as shadPS4 and fpPS4 do. That is the error the console
library returns while it has no disc bitmap loaded.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

core/libs/prx/libSceDiscMap/CMakeLists.txt

@@ -0,0 +1,15 @@
+add_library(libSceDiscMap SHARED EXCLUDE_FROM_ALL Export.cpp)
+target_include_directories(libSceDiscMap PRIVATE ${LIBS_INCLUDE_DIR})
+configure_windows_unwind(libSceDiscMap)
+
+if(BUILD_TESTING)
+    add_test_executable(guest_disc_map_tests ${LIBS_INCLUDE_DIR}/tests/GuestDiscMap.cpp)
+    target_include_directories(guest_disc_map_tests PRIVATE ${LIBS_INCLUDE_DIR})
+    target_link_libraries(guest_disc_map_tests PRIVATE libSceDiscMap libc)
+    configure_windows_unwind(guest_disc_map_tests)
+    add_test(NAME guest_disc_map COMMAND guest_disc_map_tests)
+    if(WIN32)
+        set_tests_properties(guest_disc_map PROPERTIES ENVIRONMENT_MODIFICATION
+            "PATH=path_list_prepend:$<TARGET_FILE_DIR:libSceDiscMap>")
+    endif()
+endif()

core/libs/prx/libSceDiscMap/Export.cpp

@@ -0,0 +1,32 @@
+#include <cstdint>
+#include "SceTypes.hpp"
+#include "prx/libc/include/General.hpp"
+
+namespace {
+
+constexpr std::int32_t SCE_DISC_MAP_ERROR_NO_BITMAP_INFO = static_cast<std::int32_t>(0x81100004);
+
+}
+
+extern "C" {
+
+std::int32_t APS5_VABI sceDiscMapIsRequestOnHDD(const char* path, std::int64_t offset, std::int64_t size, std::int32_t* result) {
+    (void)path;
+    (void)offset;
+    (void)size;
+    (void)result;
+    return SCE_DISC_MAP_ERROR_NO_BITMAP_INFO;
+}
+
+APS5_EXPORT("ioKMruft1ek", sceDiscMapUnknown_ioKMruft1ek);
+std::int32_t APS5_VABI sceDiscMapUnknown_ioKMruft1ek(const char* path, std::int64_t offset, std::int64_t size, void* flags, void* out1, void* out2) {
+    (void)path;
+    (void)offset;
+    (void)size;
+    (void)flags;
+    (void)out1;
+    (void)out2;
+    return SCE_DISC_MAP_ERROR_NO_BITMAP_INFO;
+}
+
+}

core/libs/tests/GuestDiscMap.cpp

@@ -0,0 +1,36 @@
+#include "prx/libc/include/general/VabiMacros.hpp"
+
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+
+extern "C" {
+std::int32_t APS5_VABI sceDiscMapIsRequestOnHDD(const char* path, std::int64_t offset, std::int64_t size, std::int32_t* result);
+std::int32_t APS5_VABI sceDiscMapUnknown_ioKMruft1ek(const char* path, std::int64_t offset, std::int64_t size, void* flags, void* out1, void* out2);
+}
+
+namespace {
+
+constexpr std::int32_t noBitmapInfo = static_cast<std::int32_t>(0x81100004);
+
+void Require(bool condition, const char* message) {
+    if (!condition) {
+        std::fprintf(stderr, "DiscMap: %s\n", message);
+        std::abort();
+    }
+}
+
+}
+
+int main() {
+    std::int32_t result = 0x5a5a5a5a;
+    Require(sceDiscMapIsRequestOnHDD("/app0/data.bin", 0, 0x10000, &result) == noBitmapInfo, "sceDiscMapIsRequestOnHDD did not report the missing bitmap");
+    Require(result == 0x5a5a5a5a, "sceDiscMapIsRequestOnHDD wrote its result");
+    std::uint64_t flags = ~0ull;
+    std::uint64_t out1 = ~0ull;
+    std::uint64_t out2 = ~0ull;
+    Require(sceDiscMapUnknown_ioKMruft1ek("/app0/data.bin", 0x8000, 0x10000, &flags, &out1, &out2) == noBitmapInfo, "ioKMruft1ek did not report the missing bitmap");
+    Require(flags == ~0ull && out1 == ~0ull && out2 == ~0ull, "ioKMruft1ek wrote an output");
+    std::puts("DiscMap tests passed");
+    return 0;
+}

docs/dev/debt/libSceDiscMap.md

@@ -0,0 +1,9 @@
+# libSceDiscMap technical debt
+
+### Silent stubs
+
+- [libSceDiscMap](../../../core/libs/prx/libSceDiscMap/Export.cpp) implements only the state with no disc bitmap: `sceDiscMapIsRequestOnHDD` and `ioKMruft1ek` return `SCE_DISC_MAP_ERROR_NO_BITMAP_INFO` (0x81100004) for every request and write nothing. CUSA02636's bundled `libSceFios2.prx` imports both; what it does with the error is not known (shadPS4 returns the same, and [shadps4-game-compatibility #617](https://github.com/shadps4-compatibility/shadps4-game-compatibility/issues/617) lists CUSA02636 as in-game)
+
+### Unknown function info
+
+- [sceDiscMapIsRequestOnHDD, sceDiscMapUnknown_ioKMruft1ek](../../../core/libs/prx/libSceDiscMap/Export.cpp) (libSceDiscMap, NIDs `lbQKqsERhtE` and `ioKMruft1ek`) - `ioKMruft1ek` has no known name. The `(path, offset, size, result)` and `(path, offset, size, flags, out1, out2)` signatures follow [shadPS4 disc_map.cpp](https://github.com/shadps4-emu/shadPS4/blob/b2d7ec7d31f9ad9426db93afe079db8679b3e1e0/src/core/libraries/disc_map/disc_map.cpp); the widths of the `ioKMruft1ek` outputs are unknown (shadPS4 `int*`, [fpPS4](https://github.com/red-prig/fpPS4/blob/04cefd43e6fddd1ab033e7980cd356d14c964905/src/ps4_libscediscmap.pas) `PInt64`), so they are `void*`. The error code is the one both return; [shadPS4 #2686](https://github.com/shadps4-emu/shadPS4/pull/2686) reads the console library as checking an initialisation global first in each call and returning it while the global is clear. Not measured on a console