diff --git a/src/lib.rs b/src/lib.rs
index ecc1cc9980..a250ebb6d7 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,4 +1,5 @@
 #![no_std]
+#![feature(offset_of)]
 //! A super simple initfs, only meant to be loaded into RAM by the bootloader, and then directly be
 //! read.
 
diff --git a/src/types.rs b/src/types.rs
index 24508fcfbc..6faf321db5 100644
--- a/src/types.rs
+++ b/src/types.rs
@@ -1,3 +1,5 @@
+use core::mem::offset_of;
+
 pub const MAGIC_LEN: usize = 8;
 pub const MAGIC: [u8; 8] = *b"RedoxFtw";
 
@@ -69,8 +71,15 @@ pub struct Header {
     pub inode_table_offset: Offset,
     pub creation_time: Timespec,
     pub inode_count: U16,
+    pub bootstrap_entry: U64,
+    pub initfs_size: U64,
 }
 
+const _: () = {
+    // Ensure the offsets of field used by the bootloader stay stable.
+    assert!(offset_of!(Header, bootstrap_entry) == 0x1a);
+};
+
 #[repr(packed)]
 #[derive(Clone, Copy, Debug)]
 pub struct InodeHeader {
diff --git a/tests/archive_and_read.rs b/tests/archive_and_read.rs
index d26df6c71a..ac4f87caaf 100644
--- a/tests/archive_and_read.rs
+++ b/tests/archive_and_read.rs
@@ -14,6 +14,7 @@ fn archive_and_read() -> Result<()> {
     let args = self::archive::Args {
         destination_path: Path::new("out.img"),
         source: Path::new("data"),
+        bootstrap_code: None,
         max_size: self::archive::DEFAULT_MAX_SIZE,
     };
     self::archive::archive(&args).context("failed to archive")?;
diff --git a/tools/src/archive_common.rs b/tools/src/archive_common.rs
index a340aeecad..b7a0b250b9 100644
--- a/tools/src/archive_common.rs
+++ b/tools/src/archive_common.rs
@@ -355,8 +355,16 @@ pub struct Args<'a> {
     pub destination_path: &'a Path,
     pub max_size: u64,
     pub source: &'a Path,
+    pub bootstrap_code: Option<&'a Path>,
 }
-pub fn archive(&Args { destination_path, max_size, source }: &Args) -> Result<()> {
+pub fn archive(
+    &Args {
+        destination_path,
+        max_size,
+        source,
+        bootstrap_code,
+    }: &Args,
+) -> Result<()> {
     let previous_extension = destination_path.extension().map_or("", |ext| {
         ext.to_str()
             .expect("expected destination path to be valid UTF-8")
@@ -407,15 +415,30 @@ pub fn archive(&Args { destination_path, max_size, source }: &Args) -> Result<()
     log::debug!("there are {} inodes", state.inode_count);
 
     // NOTE: The header is always stored at offset zero.
-    let header_offset = bump_alloc(
-        &mut state,
-        std::mem::size_of::<initfs::Header>()
-            .try_into()
-            .expect("expected header size to fit"),
-        "allocate header",
-    )?;
+    let header_offset = bump_alloc(&mut state, 4096, "allocate header")?;
     assert_eq!(header_offset, 0);
 
+    let bootstrap_entry = if let Some(bootstrap_code) = bootstrap_code {
+        allocate_and_write_file(
+            &mut state,
+            &File::open(bootstrap_code).with_context(|| {
+                anyhow!(
+                    "failed to open bootstrap code file `{}`",
+                    bootstrap_code.to_string_lossy(),
+                )
+            })?,
+        )?;
+        let bootstrap_data = std::fs::read(bootstrap_code).with_context(|| {
+            anyhow!(
+                "failed to read bootstrap code file `{}`",
+                bootstrap_code.to_string_lossy(),
+            )
+        })?;
+        elf_entry(&bootstrap_data)
+    } else {
+        u64::MAX
+    };
+
     let inode_table_length = {
         let inode_entry_size: u64 = std::mem::size_of::<initfs::InodeHeader>()
             .try_into()
@@ -463,6 +486,8 @@ pub fn archive(&Args { destination_path, max_size, source }: &Args) -> Result<()
             },
             inode_count: state.inode_count.into(),
             inode_table_offset,
+            bootstrap_entry: bootstrap_entry.into(),
+            initfs_size: state.file.metadata().context("failed to get initfs size")?.len().into(),
         };
         write_all_at(&*state.file, &header_bytes, header_offset, "writing header")
             .context("failed to write header")?;
@@ -475,3 +500,28 @@ pub fn archive(&Args { destination_path, max_size, source }: &Args) -> Result<()
 
     Ok(())
 }
+
+fn elf_entry(data: &[u8]) -> u64 {
+    assert!(&data[..4] == b"\x7FELF");
+    match (data[4], data[5]) {
+        // 32-bit, little endian
+        (1, 1) => u32::from_le_bytes(
+            <[u8; 4]>::try_from(&data[0x18..0x18 + 4]).expect("conversion cannot fail"),
+        ) as u64,
+        // 32-bit, big endian
+        (1, 2) => u32::from_be_bytes(
+            <[u8; 4]>::try_from(&data[0x18..0x18 + 4]).expect("conversion cannot fail"),
+        ) as u64,
+        // 64-bit, little endian
+        (2, 1) => u64::from_le_bytes(
+            <[u8; 8]>::try_from(&data[0x18..0x18 + 8]).expect("conversion cannot fail"),
+        ),
+        // 64-bit, big endian
+        (2, 2) => u64::from_be_bytes(
+            <[u8; 8]>::try_from(&data[0x18..0x18 + 8]).expect("conversion cannot fail"),
+        ),
+        (ei_class, ei_data) => {
+            panic!("Unsupported ELF EI_CLASS {} EI_DATA {}", ei_class, ei_data);
+        }
+    }
+}
diff --git a/tools/src/bin/archive.rs b/tools/src/bin/archive.rs
index 6fc48c66b4..5258f75ee3 100644
--- a/tools/src/bin/archive.rs
+++ b/tools/src/bin/archive.rs
@@ -24,6 +24,11 @@ fn main() -> Result<()> {
                 .required(true)
                 .help("Specify the source directory to build the image from."),
         )
+        .arg(
+            Arg::new("BOOTSTRAP_CODE")
+                .required(false)
+                .help("Specify the bootstrap ELF file to include in the image.")
+        )
         .arg(
             Arg::new("OUTPUT")
                 .required(true)
@@ -47,12 +52,15 @@ fn main() -> Result<()> {
         .get_one::<String>("SOURCE")
         .expect("expected the required arg SOURCE to exist");
 
+    let bootstrap_code = matches.get_one::<String>("BOOTSTRAP_CODE");
+
     let destination = matches
         .get_one::<String>("OUTPUT")
         .expect("expected the required arg OUTPUT to exist");
 
     let args = Args {
         source: Path::new(source),
+        bootstrap_code: bootstrap_code.map(|bootstrap_code| Path::new(bootstrap_code)),
         destination_path: Path::new(destination),
         max_size,
     };