Implement OS Restart on Linux. (#50)

UnleashedRecomp/os/linux/process_linux.cpp

@@ -1,20 +1,57 @@
 #include <os/process_detail.h>
 
+#include <signal.h>
+
 std::filesystem::path os::process::detail::GetExecutablePath()
 {
-    assert(false && "Unimplemented.");
+    char exePath[PATH_MAX] = {};
-    return std::filesystem::path();
+    if (readlink("/proc/self/exe", exePath, PATH_MAX) > 0)
+    {
+        return std::filesystem::path(std::u8string_view((const char8_t*)(exePath)));
+    }
+    else
+    {
+        return std::filesystem::path();
+    }
 }
 
 std::filesystem::path os::process::detail::GetWorkingDirectory()
 {
-    // TODO: There's a cross platform way to retrieve this which is just getting it from argv[0].
+    char cwd[PATH_MAX] = {};
-    assert(false && "Unimplemented.");
+    char *res = getcwd(cwd, sizeof(cwd));
-    return std::filesystem::path();
+    if (res != nullptr)
+    {
+        return std::filesystem::path(std::u8string_view((const char8_t*)(cwd)));
+    }
+    else
+    {
+        return std::filesystem::path();
+    }
 }
 
 bool os::process::detail::StartProcess(const std::filesystem::path path, const std::vector<std::string> args, std::filesystem::path work)
 {
-    assert(false && "Unimplemented.");
+    pid_t pid = fork();
-    return false;
+    if (pid < 0)
+        return false;
+
+    if (pid == 0)
+    {
+        setsid();
+        
+        std::u8string workU8 = work.u8string();
+        chdir((const char*)(workU8.c_str())); 
+        
+        std::u8string pathU8 = path.u8string();
+        std::vector<char*> argStrs;
+        argStrs.push_back((char*)(pathU8.c_str()));
+        for (const std::string& arg : args)
+            argStrs.push_back((char *)(arg.c_str()));
+        
+        argStrs.push_back(nullptr);
+        execvp((const char*)(pathU8.c_str()), argStrs.data());
+        raise(SIGKILL);
+    }
+
+    return true;
 }