Change Config to make fastmem_pointer of zero valid.

This changes Dynarmic::A32/A64::Config to store fastmem_pointer in
a std::optional<uintptr_t>, allowing the user to pass a zero base
address for the guest memory, which can be used to effectively
implement a shared address space between the host and the guest.

src/dynarmic/backend/arm64/a32_address_space.cpp

@@ -233,7 +233,7 @@ void A32AddressSpace::EmitPrelude() {
             code.MOV(Xpagetable, mcl::bit_cast<u64>(conf.page_table));
         }
         if (conf.fastmem_pointer) {
-            code.MOV(Xfastmem, mcl::bit_cast<u64>(conf.fastmem_pointer));
+            code.MOV(Xfastmem, *conf.fastmem_pointer);
         }
 
         if (conf.HasOptimization(OptimizationFlag::ReturnStackBuffer)) {
@@ -272,7 +272,7 @@ void A32AddressSpace::EmitPrelude() {
             code.MOV(Xpagetable, mcl::bit_cast<u64>(conf.page_table));
         }
         if (conf.fastmem_pointer) {
-            code.MOV(Xfastmem, mcl::bit_cast<u64>(conf.fastmem_pointer));
+            code.MOV(Xfastmem, *conf.fastmem_pointer);
         }
 
         if (conf.HasOptimization(OptimizationFlag::ReturnStackBuffer)) {
@@ -388,7 +388,7 @@ EmitConfig A32AddressSpace::GetEmitConfig() {
         .detect_misaligned_access_via_page_table = conf.detect_misaligned_access_via_page_table,
         .only_detect_misalignment_via_page_table_on_page_boundary = conf.only_detect_misalignment_via_page_table_on_page_boundary,
 
-        .fastmem_pointer = mcl::bit_cast<u64>(conf.fastmem_pointer),
+        .fastmem_pointer = conf.fastmem_pointer,
         .recompile_on_fastmem_failure = conf.recompile_on_fastmem_failure,
         .fastmem_address_space_bits = 32,
         .silently_mirror_fastmem = true,

src/dynarmic/backend/arm64/a64_address_space.cpp

@@ -411,7 +411,7 @@ void A64AddressSpace::EmitPrelude() {
             code.MOV(Xpagetable, mcl::bit_cast<u64>(conf.page_table));
         }
         if (conf.fastmem_pointer) {
-            code.MOV(Xfastmem, mcl::bit_cast<u64>(conf.fastmem_pointer));
+            code.MOV(Xfastmem, *conf.fastmem_pointer);
         }
 
         if (conf.HasOptimization(OptimizationFlag::ReturnStackBuffer)) {
@@ -449,7 +449,7 @@ void A64AddressSpace::EmitPrelude() {
             code.MOV(Xpagetable, mcl::bit_cast<u64>(conf.page_table));
         }
         if (conf.fastmem_pointer) {
-            code.MOV(Xfastmem, mcl::bit_cast<u64>(conf.fastmem_pointer));
+            code.MOV(Xfastmem, *conf.fastmem_pointer);
         }
 
         if (conf.HasOptimization(OptimizationFlag::ReturnStackBuffer)) {
@@ -564,7 +564,7 @@ EmitConfig A64AddressSpace::GetEmitConfig() {
         .detect_misaligned_access_via_page_table = conf.detect_misaligned_access_via_page_table,
         .only_detect_misalignment_via_page_table_on_page_boundary = conf.only_detect_misalignment_via_page_table_on_page_boundary,
 
-        .fastmem_pointer = mcl::bit_cast<u64>(conf.fastmem_pointer),
+        .fastmem_pointer = conf.fastmem_pointer,
         .recompile_on_fastmem_failure = conf.recompile_on_fastmem_failure,
         .fastmem_address_space_bits = conf.fastmem_address_space_bits,
         .silently_mirror_fastmem = conf.silently_mirror_fastmem,

src/dynarmic/backend/arm64/emit_arm64.h

@@ -132,7 +132,7 @@ struct EmitConfig {
     bool only_detect_misalignment_via_page_table_on_page_boundary;
 
     // Fastmem
-    u64 fastmem_pointer;
+    std::optional<u64> fastmem_pointer;
     bool recompile_on_fastmem_failure;
     size_t fastmem_address_space_bits;
     bool silently_mirror_fastmem;

src/dynarmic/backend/x64/a32_interface.cpp

@@ -47,7 +47,7 @@ static std::function<void(BlockOfCode&)> GenRCP(const A32::UserConfig& conf) {
             code.mov(code.r14, mcl::bit_cast<u64>(conf.page_table));
         }
         if (conf.fastmem_pointer) {
-            code.mov(code.r13, mcl::bit_cast<u64>(conf.fastmem_pointer));
+            code.mov(code.r13, *conf.fastmem_pointer);
         }
     };
 }

src/dynarmic/backend/x64/a64_interface.cpp

@@ -43,7 +43,7 @@ static std::function<void(BlockOfCode&)> GenRCP(const A64::UserConfig& conf) {
             code.mov(code.r14, mcl::bit_cast<u64>(conf.page_table));
         }
         if (conf.fastmem_pointer) {
-            code.mov(code.r13, mcl::bit_cast<u64>(conf.fastmem_pointer));
+            code.mov(code.r13, *conf.fastmem_pointer);
         }
     };
 }

src/dynarmic/interface/A32/config.h

@@ -182,7 +182,7 @@ struct UserConfig {
     // This should point to the beginning of a 4GB address space which is in arranged just like
     // what you wish for emulated memory to be. If the host page faults on an address, the JIT
     // will fallback to calling the MemoryRead*/MemoryWrite* callbacks.
-    void* fastmem_pointer = nullptr;
+    std::optional<uintptr_t> fastmem_pointer = std::nullopt;
     /// Determines if instructions that pagefault should cause recompilation of that block
     /// with fastmem disabled.
     /// Recompiled code will use the page_table if this is available, otherwise memory

src/dynarmic/interface/A64/config.h

@@ -241,7 +241,7 @@ struct UserConfig {
     /// address space which is in arranged just like what you wish for emulated memory to
     /// be. If the host page faults on an address, the JIT will fallback to calling the
     /// MemoryRead*/MemoryWrite* callbacks.
-    void* fastmem_pointer = nullptr;
+    std::optional<uintptr_t> fastmem_pointer = std::nullopt;
     /// Determines if instructions that pagefault should cause recompilation of that block
     /// with fastmem disabled.
     /// Recompiled code will use the page_table if this is available, otherwise memory
@@ -249,13 +249,13 @@ struct UserConfig {
     bool recompile_on_fastmem_failure = true;
     /// Declares how many valid address bits are there in virtual addresses.
     /// Determines the size of fastmem arena. Valid values are between 12 and 64 inclusive.
-    /// This is only used if fastmem_pointer is not nullptr.
+    /// This is only used if fastmem_pointer is set.
     size_t fastmem_address_space_bits = 36;
     /// Determines what happens if the guest accesses an entry that is off the end of the
     /// fastmem arena. If true, Dynarmic will silently mirror fastmem's address space. If
     /// false, accessing memory outside of fastmem bounds will result in a call to the
     /// relevant memory callback.
-    /// This is only used if fastmem_pointer is not nullptr.
+    /// This is only used if fastmem_pointer is set.
     bool silently_mirror_fastmem = true;
 
     /// Determines if we should use the above fastmem_pointer for exclusive reads and

tests/A32/test_arm_instructions.cpp

@@ -540,7 +540,7 @@ TEST_CASE("arm: Memory access (fastmem)", "[arm][A32]") {
 
     A32FastmemTestEnv env{backing_memory};
     Dynarmic::A32::UserConfig config{&env};
-    config.fastmem_pointer = backing_memory;
+    config.fastmem_pointer = reinterpret_cast<uintptr_t>(backing_memory);
     config.recompile_on_fastmem_failure = false;
     config.processor_id = 0;