diff --git a/util/process_wrapper/flags.rs b/util/process_wrapper/flags.rs
new file mode 100644
index 0000000..d3d6fe5
--- /dev/null
+++ b/util/process_wrapper/flags.rs
@@ -0,0 +1,276 @@
+// Copyright 2020 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use std::collections::{BTreeMap, HashSet};
+use std::error::Error;
+use std::fmt;
+use std::fmt::Write;
+use std::iter::Peekable;
+use std::mem::take;
+
+#[derive(Debug, Clone)]
+pub(crate) enum FlagParseError {
+    UnknownFlag(String),
+    ValueMissing(String),
+    ProvidedMultipleTimes(String),
+    ProgramNameMissing,
+}
+
+impl fmt::Display for FlagParseError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Self::UnknownFlag(ref flag) => write!(f, "unknown flag \"{}\"", flag),
+            Self::ValueMissing(ref flag) => write!(f, "flag \"{}\" missing parameter(s)", flag),
+            Self::ProvidedMultipleTimes(ref flag) => {
+                write!(f, "flag \"{}\" can only appear once", flag)
+            }
+            Self::ProgramNameMissing => {
+                write!(f, "program name (argv[0]) missing")
+            }
+        }
+    }
+}
+impl Error for FlagParseError {}
+
+struct FlagDef<'a, T> {
+    name: String,
+    help: String,
+    output_storage: &'a mut Option<T>,
+}
+
+impl<'a, T> fmt::Display for FlagDef<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}\t{}", self.name, self.help)
+    }
+}
+
+impl<'a, T> fmt::Debug for FlagDef<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("FlagDef")
+            .field("name", &self.name)
+            .field("help", &self.help)
+            .finish()
+    }
+}
+
+#[derive(Debug)]
+pub(crate) struct Flags<'a> {
+    single: BTreeMap<String, FlagDef<'a, String>>,
+    repeated: BTreeMap<String, FlagDef<'a, Vec<String>>>,
+}
+
+#[derive(Debug)]
+pub(crate) enum ParseOutcome {
+    Help(String),
+    Parsed(Vec<String>),
+}
+
+impl<'a> Flags<'a> {
+    pub(crate) fn new() -> Flags<'a> {
+        Flags {
+            single: BTreeMap::new(),
+            repeated: BTreeMap::new(),
+        }
+    }
+
+    pub(crate) fn define_flag(
+        &mut self,
+        name: impl Into<String>,
+        help: impl Into<String>,
+        output_storage: &'a mut Option<String>,
+    ) {
+        let name = name.into();
+        if self.repeated.contains_key(&name) {
+            panic!("argument \"{}\" already defined as repeated flag", name)
+        }
+        self.single.insert(
+            name.clone(),
+            FlagDef::<'a, String> {
+                name,
+                help: help.into(),
+                output_storage,
+            },
+        );
+    }
+
+    pub(crate) fn define_repeated_flag(
+        &mut self,
+        name: impl Into<String>,
+        help: impl Into<String>,
+        output_storage: &'a mut Option<Vec<String>>,
+    ) {
+        let name = name.into();
+        if self.single.contains_key(&name) {
+            panic!("argument \"{}\" already defined as flag", name)
+        }
+        self.repeated.insert(
+            name.clone(),
+            FlagDef::<'a, Vec<String>> {
+                name,
+                help: help.into(),
+                output_storage,
+            },
+        );
+    }
+
+    fn help(&self, program_name: String) -> String {
+        let single = self.single.values().map(|fd| fd.to_string());
+        let repeated = self.repeated.values().map(|fd| fd.to_string());
+        let mut all: Vec<String> = single.chain(repeated).collect();
+        all.sort();
+
+        let mut help_text = String::new();
+        writeln!(
+            &mut help_text,
+            "Help for {}: [options] -- [extra arguments]",
+            program_name
+        )
+        .unwrap();
+        for line in all {
+            writeln!(&mut help_text, "\t{}", line).unwrap();
+        }
+        help_text
+    }
+
+    pub(crate) fn parse(mut self, argv: Vec<String>) -> Result<ParseOutcome, FlagParseError> {
+        let mut argv_iter = argv.into_iter().peekable();
+        let program_name = argv_iter.next().ok_or(FlagParseError::ProgramNameMissing)?;
+
+        // To check if a non-repeated flag has been set already.
+        let mut seen_single_flags = HashSet::<String>::new();
+
+        while let Some(flag) = argv_iter.next() {
+            if flag == "--help" {
+                return Ok(ParseOutcome::Help(self.help(program_name)));
+            }
+            if !flag.starts_with("--") {
+                return Err(FlagParseError::UnknownFlag(flag));
+            }
+            let mut args = consume_args(&flag, &mut argv_iter);
+            if flag == "--" {
+                return Ok(ParseOutcome::Parsed(args));
+            }
+            if args.is_empty() {
+                return Err(FlagParseError::ValueMissing(flag.clone()));
+            }
+            if let Some(flag_def) = self.single.get_mut(&flag) {
+                if args.len() > 1 || seen_single_flags.contains(&flag) {
+                    return Err(FlagParseError::ProvidedMultipleTimes(flag.clone()));
+                }
+                let arg = args.first_mut().unwrap();
+                seen_single_flags.insert(flag);
+                *flag_def.output_storage = Some(take(arg));
+                continue;
+            }
+            if let Some(flag_def) = self.repeated.get_mut(&flag) {
+                flag_def
+                    .output_storage
+                    .get_or_insert_with(Vec::new)
+                    .append(&mut args);
+                continue;
+            }
+            return Err(FlagParseError::UnknownFlag(flag));
+        }
+        Ok(ParseOutcome::Parsed(vec![]))
+    }
+}
+
+fn consume_args<I: Iterator<Item = String>>(
+    flag: &str,
+    argv_iter: &mut Peekable<I>,
+) -> Vec<String> {
+    if flag == "--" {
+        // If we have found --, the rest of the iterator is just returned as-is.
+        argv_iter.collect()
+    } else {
+        let mut args = vec![];
+        while let Some(arg) = argv_iter.next_if(|s| !s.starts_with("--")) {
+            args.push(arg);
+        }
+        args
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    fn args(args: &[&str]) -> Vec<String> {
+        ["foo"].iter().chain(args).map(|&s| s.to_owned()).collect()
+    }
+
+    #[test]
+    fn test_flag_help() {
+        let mut bar = None;
+        let mut parser = Flags::new();
+        parser.define_flag("--bar", "bar help", &mut bar);
+        let result = parser.parse(args(&["--help"])).unwrap();
+        if let ParseOutcome::Help(h) = result {
+            assert!(h.contains("Help for foo"));
+            assert!(h.contains("--bar\tbar help"));
+        } else {
+            panic!("expected that --help would invoke help, instead parsed arguments")
+        }
+    }
+
+    #[test]
+    fn test_flag_single_repeated() {
+        let mut bar = None;
+        let mut parser = Flags::new();
+        parser.define_flag("--bar", "bar help", &mut bar);
+        let result = parser.parse(args(&["--bar", "aa", "bb"]));
+        if let Err(FlagParseError::ProvidedMultipleTimes(f)) = result {
+            assert_eq!(f, "--bar");
+        } else {
+            panic!("expected error, got {:?}", result)
+        }
+        let mut parser = Flags::new();
+        parser.define_flag("--bar", "bar help", &mut bar);
+        let result = parser.parse(args(&["--bar", "aa", "--bar", "bb"]));
+        if let Err(FlagParseError::ProvidedMultipleTimes(f)) = result {
+            assert_eq!(f, "--bar");
+        } else {
+            panic!("expected error, got {:?}", result)
+        }
+    }
+
+    #[test]
+    fn test_repeated_flags() {
+        // Test case 1) --bar something something_else should work as a repeated flag.
+        let mut bar = None;
+        let mut parser = Flags::new();
+        parser.define_repeated_flag("--bar", "bar help", &mut bar);
+        let result = parser.parse(args(&["--bar", "aa", "bb"])).unwrap();
+        assert!(matches!(result, ParseOutcome::Parsed(_)));
+        assert_eq!(bar, Some(vec!["aa".to_owned(), "bb".to_owned()]));
+        // Test case 2) --bar something --bar something_else should also work as a repeated flag.
+        bar = None;
+        let mut parser = Flags::new();
+        parser.define_repeated_flag("--bar", "bar help", &mut bar);
+        let result = parser.parse(args(&["--bar", "aa", "--bar", "bb"])).unwrap();
+        assert!(matches!(result, ParseOutcome::Parsed(_)));
+        assert_eq!(bar, Some(vec!["aa".to_owned(), "bb".to_owned()]));
+    }
+
+    #[test]
+    fn test_extra_args() {
+        let parser = Flags::new();
+        let result = parser.parse(args(&["--", "bb"])).unwrap();
+        if let ParseOutcome::Parsed(got) = result {
+            assert_eq!(got, vec!["bb".to_owned()])
+        } else {
+            panic!("expected correct parsing, got {:?}", result)
+        }
+    }
+}