Tools/pidof: Fixes FEXpidof after #5097

FEX argument will no longer exist in `/proc/<pid>/cmdline` after this
PR. Ensure this tool still works.

After #5097 is merged, one can use regular `pidof` for Linux
applications, but this is still useful as it finds Wine applications
running with FEX as well.

Source/Tools/pidof/pidof.cpp

@@ -19,6 +19,7 @@ namespace Config {
 bool SingleShot {};
 bool SkipZombie {true};
 bool DoNotDisplay {};
+bool AllFEX {};
 std::string Separator {" "};
 std::unordered_set<int64_t> OmitPids;
 std::unordered_set<std::string> Programs;
@@ -65,6 +66,9 @@ void LoadOptions(int argc, char** argv) {
   }
 
   for (const auto& Program : Parser.args()) {
+    if (Program == "FEX") {
+      AllFEX = true;
+    }
     Programs.emplace(Program);
   }
 }
@@ -239,14 +243,6 @@ int main(int argc, char** argv) {
       arg += strlen(arg) + 1;
     }
 
-    auto FindFEXArgument = [](auto& Path) -> int32_t {
-      if (Path.ends_with("FEX")) {
-        return 1;
-      }
-
-      return -1;
-    };
-
     struct ProgramPair {
       std::string_view ProgramPath;
       std::string_view ProgramFilename;
@@ -303,20 +299,24 @@ int main(int argc, char** argv) {
     };
 
     int32_t ProgramArg = -1;
-    ProgramArg = FindFEXArgument(pid.exe_link);
-    if (ProgramArg == -1) {
-      ProgramArg = FindFEXArgument(Args[0]);
+    if (pid.exe_link.ends_with("FEX")) {
+      // Skip the first argument if it contains `FEX`, otherwise the application name begins at 0.
+      ProgramArg = Args[0].ends_with("FEX") ? 1 : 0;
+    }
+
+    // If matching all "FEX" instances then add to the matched list.
+    if (ProgramArg != -1 && Config::AllFEX) {
+      MatchedPIDs.emplace(pid.pid);
+      continue;
     }
 
     bool IsWine = false;
-    if (ProgramArg == -1) {
-      // If we still haven't found a FEX path then this might be an arm64ec FEX application.
-      // The only way to know for sure is the walk the mapped files of the process and check if FEX is mapped.
-      if (FindWineFEXApplication(pid.pid, pid.exe_link, Args)) {
-        // Search from the start.
-        ProgramArg = 0;
-        IsWine = true;
-      }
+    // If we still haven't found a FEX path then this might be an arm64ec FEX application.
+    // The only way to know for sure is the walk the mapped files of the process and check if FEX is mapped.
+    if (FindWineFEXApplication(pid.pid, pid.exe_link, Args)) {
+      // Search from the start.
+      ProgramArg = 0;
+      IsWine = true;
     }
 
     if (ProgramArg == -1 || ProgramArg >= Args.size()) {