Refactor

CMakeLists.txt

@@ -19,6 +19,7 @@ add_executable(runtime
 )
 
 # QEMU
+include(CheckSymbolExists)
 check_symbol_exists("__x86_64__" "" USE_QEMU)
 if(USE_QEMU)
     add_subdirectory(qemu)
@@ -39,9 +40,13 @@ target_link_libraries(runtime
     trampoline-headers
 )
 
+# External Library
+set(TRAMPOLINE_LIBRARY_NAME "trampoline" CACHE STRING "Trampoline Library That The Runtime Uses")
+target_compile_definitions(runtime PRIVATE "TRAMPOLINE_LIBRARY=\"lib${TRAMPOLINE_LIBRARY_NAME}.so\"")
+
 # Install
-if(DEFINED MCPI_BIN_DIR)
-    install(TARGETS runtime DESTINATION "${MCPI_BIN_DIR}")
+if(DEFINED MCPI_LIB_DIR)
+    install(TARGETS runtime DESTINATION "${MCPI_LIB_DIR}")
     # License
     install(FILES "${CMAKE_CURRENT_SOURCE_DIR}/LICENSE" DESTINATION "${MCPI_LEGAL_DIR}/${PROJECT_NAME}")
 endif()

README.md

@@ -1,13 +1,13 @@
 # Reborn Runtime
 This is a simple program allowing ARM32 code to easily call "native" code.
 
-By running an ARM32 program inside this runtime, it gains the ability to call `raw_trampoline`. This function copies its arguments and passes them to the `trampoline` function inside `libmedia-layer-trampoline.so`.
+By running an ARM32 program inside this runtime, it gains the ability to call `raw_trampoline`. This function copies its arguments and passes them to the `trampoline` function inside `libtrampoline.so`.
 
 The runtime also automatically uses QEMU on x86_64 systems.
 
 ## Terminology
-- "Guest" code is the main ARM32 program.
-- "Host" code is the native code located in `libmedia-layer-trampoline.so`.
+- "Guest" code is the main ARM32 program. It is running inside the runtime.
+- "Host" code is the native code located in `libtrampoline.so`. It is running "alongside" the runtime.
 
 ## Example
 There is a simple C example [here](./example). It sends a given string to the host, which returns the string's length multiplied by two.
@@ -15,7 +15,7 @@ There is a simple C example [here](./example). It sends a given string to the ho
 ## Early Returning
 `raw_trampoline` supports returning before the host code has finished executing. This can be enabled by passing `true` to `allow_early_return`. However, this is only supported in certain circumstances, can cause race-conditions, and prevents the guest code from receiving the host's return value.
 
-## Syscall Versus Pipe Trampolines
+## Syscall Vs. Pipe Trampolines
 The runtime supports two methods of passing data between the guest and host.
 - System Call
   - Data is passed through a custom system-call added to QEMU.

example/build.sh

@@ -13,30 +13,21 @@ out 'set -e'
 chmod +x "${RUN}"
 
 # Create Build Directory
-rm -rf build
 dir() {
-    mkdir "$1"
+    mkdir -p "$1"
     cd "$1"
 }
 dir build
 
-# Build Runtime
-dir runtime
-build() {
-    cmake -GNinja "../../$1"
-    cmake --build .
-}
-build ../
-out "export PATH=\"$(pwd):\${PATH}\""
-cd ../
-
 # Build Host Component
 build_example_part() {
     dir "$1"
-    build "$1"
+    cmake -GNinja "../../$1"
+    cmake --build .
 }
 build_example_part host
 out "export LD_LIBRARY_PATH=\"$(pwd):\${LD_LIBRARY_PATH}\""
+out "export PATH=\"$(pwd)/runtime:\${PATH}\""
 cd ../
 
 # Build Guest Component

example/guest/CMakeLists.txt

@@ -10,7 +10,7 @@ set(CMAKE_SYSTEM_PROCESSOR "arm")
 project(guest)
 
 # Build Library
-add_subdirectory(../../lib lib)
+add_subdirectory(../../ runtime)
 
 # Build
 add_executable(example src/example.c)

example/guest/src/example.c

@@ -1,19 +1,28 @@
 #include <string.h>
 #include <stdio.h>
-#include <stdlib.h>
 
 #include <trampoline/types.h>
 
+// Call Trampoline With String
 void run(uint32_t cmd, const char *str) {
-    // Arguments Must Be Modifiable
-    unsigned char *args = (unsigned char *) strdup(str);
-    // Sned Command
+    unsigned char *args = (unsigned char *) str;
+    // Send Command
     fprintf(stderr, "Guest Is Sending: %u: %s\n", cmd, str);
-    uint32_t ret = raw_trampoline(cmd, 0, strlen(str) + 1, args);
+    uint32_t ret;
+    raw_trampoline(cmd, &ret, strlen(str) + 1, args);
     fprintf(stderr, "Guest Has Received: %u\n", ret);
-    free(args);
 }
+
+// Main
+#define INFO(str) fprintf(stderr, "==== %s ====\n", str)
 int main() {
+    // Normal Calls
+    INFO("Testing Normal Trampoline Calls");
     run(0, "Hello World!");
     run(1, "Bye World!");
+    // Calls without a return value *may* return control
+    // to guest code before the call has finished.
+    INFO("Testing Trampoline Call That May Return Early");
+    raw_trampoline(100, NULL, 0, NULL);
+    fprintf(stderr, "Control Returned To Guest\n");
 }

example/host/CMakeLists.txt

@@ -4,8 +4,8 @@ cmake_minimum_required(VERSION 3.17.0)
 project(host)
 
 # Build Library
-add_subdirectory(../../lib lib)
+add_subdirectory(../../ runtime)
 
 # Build
-add_library(media-layer-trampoline SHARED src/trampoline.c)
-target_link_libraries(media-layer-trampoline trampoline-headers)
+add_library("${TRAMPOLINE_LIBRARY_NAME}" SHARED src/trampoline.c)
+target_link_libraries("${TRAMPOLINE_LIBRARY_NAME}" trampoline-headers)

example/host/src/trampoline.c

@@ -1,5 +1,6 @@
 #include <string.h>
 #include <stdio.h>
+#include <unistd.h>
 
 #include <trampoline/types.h>
 
@@ -8,7 +9,16 @@
 // args: Pointer To Command Arguments
 // Return Value: Returned To The Guest (Unless Early Return Is Enabled)
 uint32_t trampoline(trampoline_writer_t writer, uint32_t id, const unsigned char *args) {
+    if (id == 100 /* Defined In ../../guest/src/example.c */) {
+        // Early Return Allowed
+        fprintf(stderr, "Early Return Call Started\n");
+        sleep(1);
+        fprintf(stderr, "Early Return Call Done\n");
+        return 0;
+    } else {
+        // Normal Call
         const char *str = (const char *) args;
-    fprintf(stderr, "Host Has Recieved: %u: %s\n", id, str);
+        fprintf(stderr, "Host Has Received: %u: %s\n", id, str);
         return strlen(str) * 2;
+    }
 }

lib/CMakeLists.txt

@@ -1,6 +1,3 @@
-cmake_minimum_required(VERSION 3.17.0)
-
-# Start Project
 project(trampoline)
 
 # Headers
@@ -16,5 +13,9 @@ if(NOT TRAMPOLINE_IS_GUEST)
 endif()
 
 # Library To Call Trampoline
-add_library(trampoline OBJECT src/guest.cpp)
+add_library(trampoline OBJECT
+    src/lib.cpp
+    src/syscall.cpp
+    src/pipe.cpp
+)
 target_link_libraries(trampoline trampoline-headers)

lib/include/trampoline/types.h

@@ -38,7 +38,7 @@ typedef trampoline_raw_t *trampoline_t;
 
 // Call Trampoline From Guest Code
 #ifndef MCPI_BUILD_RUNTIME
-uint32_t raw_trampoline(uint32_t id, int allow_early_return, uint32_t length, unsigned char *args);
+uint32_t raw_trampoline(uint32_t id, uint32_t *ret /* Can Be Null */, uint32_t length, const unsigned char *args);
 #endif
 
 // C++

lib/src/guest.cpp

@@ -1,86 +0,0 @@
-#include <unistd.h>
-#include <string>
-#include <cstring>
-
-#include <trampoline/types.h>
-
-// Logging
-#define ERR(format, ...) \
-    ({ \
-        fprintf(stderr, "TRAMPOLINE ERROR: " format "\n", ##__VA_ARGS__); \
-        exit(EXIT_FAILURE); \
-    })
-
-// Syscall Method
-static uint32_t trampoline_syscall(const uint32_t id, unsigned char *args) {
-    // Make Syscall
-    const long ret = syscall(TRAMPOLINE_SYSCALL, id, args); // This Modifies Arguments
-    if (ret == -1) {
-        // Error
-        ERR("System Call Error: %s", strerror(errno));
-    }
-    // Return
-    return *(uint32_t *) args;
-}
-
-// Pipe Method
-static int get_pipe(const char *env) {
-    const char *value = getenv(env);
-    if (value == nullptr) {
-        ERR("Missing Variable: %s", env);
-    }
-    const std::string str = value;
-    return std::stoi(str);
-}
-static uint32_t trampoline_pipe(const uint32_t id, const bool allow_early_return, const uint32_t length, const unsigned char *args) {
-    // Get Pipes
-    static int arguments_pipe = -1;
-    static int return_value_pipe = -1;
-    if (arguments_pipe == -1) {
-        arguments_pipe = get_pipe(_MCPI_TRAMPOLINE_ARGUMENTS_ENV);
-        return_value_pipe = get_pipe(_MCPI_TRAMPOLINE_RETURN_VALUE_ENV);
-    }
-    // Write Command
-    const trampoline_pipe_arguments cmd = {
-        .id = id,
-        .allow_early_return = allow_early_return,
-        .length = length
-    };
-    if (write(arguments_pipe, &cmd, sizeof(trampoline_pipe_arguments)) != sizeof(trampoline_pipe_arguments)) {
-        ERR("Unable To Write Command");
-    }
-    // Write Arguments
-    size_t position = 0;
-    while (position < length) {
-        const ssize_t ret = write(arguments_pipe, args + position, length - position);
-        if (ret == -1) {
-            ERR("Unable To Write Arguments");
-        } else {
-            position += ret;
-        }
-    }
-    if (allow_early_return) {
-        return 0;
-    }
-    // Return
-    uint32_t ret;
-    if (read(return_value_pipe, &ret, sizeof(uint32_t)) != sizeof(uint32_t)) {
-        ERR("Unable To Read Return Value");
-    }
-    return ret;
-}
-
-// Main Function
-uint32_t raw_trampoline(const uint32_t id, const int allow_early_return, const uint32_t length, unsigned char *args) {
-    if (length > MAX_TRAMPOLINE_ARGS_SIZE) {
-        ERR("Command Too Big");
-    }
-    // Configure Method
-    static bool use_syscall = getenv(MCPI_USE_PIPE_TRAMPOLINE_ENV) == nullptr;
-    // Use Correct Method
-    if (use_syscall) {
-        return trampoline_syscall(id, args);
-    } else {
-        return trampoline_pipe(id, allow_early_return, length, args);
-    }
-}

lib/src/lib.cpp

@@ -0,0 +1,22 @@
+#include "lib.h"
+
+// Call
+static Trampoline::Error trampoline(const uint32_t id, uint32_t *ret, const uint32_t length, const unsigned char *args) {
+    // Check Arguments Length
+    if (length > MAX_TRAMPOLINE_ARGS_SIZE) {
+        return Trampoline::Error::COMMAND_TOO_BIG;
+    }
+    // Configure Method
+    static bool use_syscall = SyscallTrampoline::should_use();
+    // Use Correct Method
+    if (use_syscall) {
+        static SyscallTrampoline syscall;
+        return syscall.call(id, ret, length, args);
+    } else {
+        static PipeTrampoline pipe;
+        return pipe.call(id, ret, length, args);
+    }
+}
+uint32_t raw_trampoline(const uint32_t id, uint32_t *ret, const uint32_t length, const unsigned char *args) {
+    return uint32_t(trampoline(id, ret, length, args));
+}

lib/src/lib.h

@@ -0,0 +1,41 @@
+#pragma once
+
+#include <cstdint>
+
+#include <trampoline/types.h>
+
+// Common
+struct Trampoline {
+    virtual ~Trampoline() = default;
+    // Error Codes
+    enum class Error : uint32_t {
+        NONE = 0,
+        // Generic
+        COMMAND_TOO_BIG,
+        // System Call
+        SYSCALL,
+        // Pipe
+        MISSING_PIPE,
+        INVALID_PIPE,
+        PIPE_WRITE,
+        PIPE_READ
+    };
+    // Call
+    virtual Error call(uint32_t id, uint32_t *ret_ptr, uint32_t length, const unsigned char *args) = 0;
+};
+
+// Syscall Method
+struct SyscallTrampoline final : Trampoline {
+    static bool should_use();
+    Error call(uint32_t id, uint32_t *ret_ptr, uint32_t length, const unsigned char *args) override;
+};
+
+// Pipe Method
+struct PipeTrampoline final : Trampoline {
+    PipeTrampoline();
+    Error call(uint32_t id, uint32_t *ret_ptr, uint32_t length, const unsigned char *args) override;
+private:
+    Error status;
+    int arguments_pipe;
+    int return_value_pipe;
+};

lib/src/pipe.cpp

@@ -0,0 +1,71 @@
+#include <utility>
+#include <variant>
+#include <cstdlib>
+#include <string>
+#include <unistd.h>
+
+#include "lib.h"
+
+// Load Pipes
+static std::variant<int, Trampoline::Error> get_pipe(const char *env) {
+    const char *value = getenv(env);
+    if (value == nullptr) {
+        return Trampoline::Error::MISSING_PIPE;
+    }
+    try {
+        const int val = std::stoi(value);
+        if (val >= 0) {
+            return val;
+        }
+    } catch (...) {
+    }
+    return Trampoline::Error::INVALID_PIPE;
+}
+#define set(var, env) \
+    val = get_pipe(env); \
+    if (std::holds_alternative<Error>(val)) { \
+        status = std::get<Error>(val); \
+        return; \
+    } \
+    var = std::get<int>(val)
+PipeTrampoline::PipeTrampoline() {
+    std::variant<int, Error> val;
+    set(arguments_pipe, _MCPI_TRAMPOLINE_ARGUMENTS_ENV);
+    set(return_value_pipe, _MCPI_TRAMPOLINE_RETURN_VALUE_ENV);
+    // Success
+    status = Error::NONE;
+}
+#undef set
+
+// Call
+Trampoline::Error PipeTrampoline::call(const uint32_t id, uint32_t *ret_ptr, const uint32_t length, const unsigned char *args) {
+    // Check
+    if (status != Error::NONE) {
+        return status;
+    }
+    // Write Command
+    const trampoline_pipe_arguments cmd = {
+        .id = id,
+        .allow_early_return = ret_ptr == nullptr,
+        .length = length
+    };
+    if (write(arguments_pipe, &cmd, sizeof(trampoline_pipe_arguments)) != sizeof(trampoline_pipe_arguments)) {
+        return Error::PIPE_WRITE;
+    }
+    // Write Arguments
+    size_t position = 0;
+    while (position < length) {
+        const ssize_t ret = write(arguments_pipe, args + position, length - position);
+        if (ret == -1) {
+            return Error::PIPE_WRITE;
+        } else {
+            position += ret;
+        }
+    }
+    // Return Value
+    if (ret_ptr != nullptr && read(return_value_pipe, ret_ptr, sizeof(uint32_t)) != sizeof(uint32_t)) {
+        return Error::PIPE_READ;
+    }
+    // Success
+    return Error::NONE;
+}

lib/src/syscall.cpp

@@ -0,0 +1,14 @@
+#include <unistd.h>
+#include <cstdlib>
+
+#include "lib.h"
+
+// Check
+bool SyscallTrampoline::should_use() {
+    return getenv(MCPI_USE_PIPE_TRAMPOLINE_ENV) == nullptr;
+}
+
+// Call
+Trampoline::Error SyscallTrampoline::call(const uint32_t id, uint32_t *ret_ptr, uint32_t length, const unsigned char *args) {
+    return syscall(TRAMPOLINE_SYSCALL, id, ret_ptr, args) != 0 ? Error::SYSCALL : Error::NONE;
+}

qemu/patches/trampoline-syscall.patch

@@ -13,7 +13,7 @@
             int, __to_dfd, const char *, __to_pathname, unsigned int, flag)
  #endif
 
-+extern int trampoline_handle_syscall(int32_t num, uint32_t arg1, uint32_t arg2);
++extern int trampoline_handle_syscall(int32_t num, uint32_t arg1, uint32_t arg2, uint32_t arg3);
 +
  /* This is an internal helper for do_syscall so that it is easier
   * to have a single return point, so that actions, such as logging
@@ -22,7 +22,7 @@
  #endif
      void *p;
 
-+    if (trampoline_handle_syscall(num, arg1, arg2)) {
++    if (trampoline_handle_syscall(num, arg1, arg2, arg3)) {
 +        return 0;
 +    }
 +

src/qemu/qemu.cpp

@@ -7,6 +7,9 @@
 
 // Access QEMU's Memory
 void *QEMU::guest_to_host(const uint32_t guest_addr) {
+    if (guest_addr == 0) {
+        return nullptr;
+    }
     return (void *) (uintptr_t) (guest_addr + QEMU_GUEST_BASE);;
 }
 

src/qemu/qemu.h

@@ -9,7 +9,7 @@
 // QEMU API
 extern "C" {
     // Called By Patched QEMU
-    int trampoline_handle_syscall(int32_t num, uint32_t arg1, uint32_t arg2);
+    int trampoline_handle_syscall(int32_t num, uint32_t arg1, uint32_t arg2, uint32_t arg3);
     // Main
     int qemu_main(int argc, char **argv, char **envp);
 }

src/syscall/handler.cpp

@@ -4,18 +4,23 @@
 #include "main.h"
 
 // Handle Syscall
-int trampoline_handle_syscall(const int32_t num, const uint32_t arg1, uint32_t arg2) {
+int trampoline_handle_syscall(const int32_t num, const uint32_t arg1, const uint32_t arg2, const uint32_t arg3) {
     // Check Syscall
     if (num != TRAMPOLINE_SYSCALL) {
         return 0;
     }
     // Run
-    SyscallImplementation::instance->handle_syscall(arg1, arg2);
+    SyscallImplementation::instance->handle_syscall(arg1, arg2, arg3);
     return 1;
 }
-void SyscallImplementation::handle_syscall(const uint32_t arg1, const uint32_t arg2) const {
+void SyscallImplementation::handle_syscall(const uint32_t arg1, const uint32_t arg2, const uint32_t arg3) const {
+    // Get Arguments
     const uint32_t id = arg1;
-    const unsigned char *args = (const unsigned char *) QEMU::guest_to_host(arg2);
+    uint32_t *ret_ptr = (uint32_t *) QEMU::guest_to_host(arg2);
+    const unsigned char *args = (const unsigned char *) QEMU::guest_to_host(arg3);
+    // Call
     const uint32_t ret = trampoline(id, args);
-    *(uint32_t *) args = ret;
+    if (ret_ptr != nullptr) {
+        *ret_ptr = ret;
+    }
 }

src/syscall/main.h

@@ -5,6 +5,6 @@
 struct SyscallImplementation final : Implementation {
     int main(int argc, char *argv[]) override;
     void memory_writer(uint32_t guest_addr, const void *data, uint32_t size) const override;
-    void handle_syscall(uint32_t arg1, uint32_t arg2) const;
+    void handle_syscall(uint32_t arg1, uint32_t arg2, uint32_t arg3) const;
     static SyscallImplementation *instance;
 };

src/trampoline.cpp

@@ -20,11 +20,11 @@ uint32_t Trampoline::operator()(const uint32_t id, const unsigned char *args) co
 void Trampoline::init(const Implementation *impl) {
     stored_impl = impl;
     // Open Library
-    void *handle = dlopen("libmedia-layer-trampoline.so", RTLD_NOW);
+    void *handle = dlopen(TRAMPOLINE_LIBRARY, RTLD_NOW);
     if (handle != nullptr) {
         func = (trampoline_t) dlsym(handle, "trampoline");
     }
     if (func == nullptr) {
-        ERR("Unable To Load Media Layer Trampoline: %s", dlerror());
+        ERR("Unable To Trampoline: %s", dlerror());
     }
 }