diff --git a/Cargo.lock b/Cargo.lock
index 4e695c7..3b5f9b8 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1415,6 +1415,13 @@ checksum = "c08c74e62047bb2de4ff487b251e4a92e24f48745648451635cec7d591162d9f"
 name = "revive-builtins"
 version = "0.1.0"
 
+[[package]]
+name = "revive-extensions"
+version = "0.1.0"
+dependencies = [
+ "inkwell",
+]
+
 [[package]]
 name = "revive-integration"
 version = "0.1.0"
diff --git a/crates/extensions/Cargo.toml b/crates/extensions/Cargo.toml
new file mode 100644
index 0000000..06fc411
--- /dev/null
+++ b/crates/extensions/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "revive-extensions"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+inkwell = { workspace = true, no-default-features = true, features = ["target-riscv", "no-libffi-linking", "llvm16-0"] }
diff --git a/crates/extensions/bswap.ll b/crates/extensions/bswap.ll
new file mode 100644
index 0000000..36a4b4a
--- /dev/null
+++ b/crates/extensions/bswap.ll
@@ -0,0 +1,13 @@
+target datalayout = "e-m:e-p:32:32-i64:64-n32-S128"
+target triple = "riscv32-unknown-unknown-elf"
+
+define dso_local noundef i256 @__bswap(i256 noundef %0) local_unnamed_addr #0 {
+  %2 = tail call i256 @llvm.bswap.i256(i256 %0)
+  ret i256 %2
+}
+
+; Function Attrs: mustprogress nocallback nofree nosync nounwind speculatable willreturn memory(none)
+declare i256 @llvm.bswap.i256(i256) #1
+
+attributes #0 = { alwaysinline mustprogress nofree norecurse nosync nounwind willreturn memory(none) }
+attributes #1 = { mustprogress nocallback nofree nosync nounwind speculatable willreturn memory(none) }
diff --git a/crates/extensions/build.rs b/crates/extensions/build.rs
new file mode 100644
index 0000000..c7b657a
--- /dev/null
+++ b/crates/extensions/build.rs
@@ -0,0 +1,40 @@
+use std::{env, fs, path::Path, process::Command};
+
+fn compile(source_path: &str, output_path: &str) {
+    let output = Command::new("llc")
+        .args([
+            "-O3",
+            "-filetype=asm",
+            "-mattr=+zbb,+e",
+            source_path,
+            "-o",
+            output_path,
+        ])
+        .output()
+        .expect("should be able to invoke llc");
+
+    assert!(
+        output.status.success(),
+        "failed to compile {}: {:?}",
+        source_path,
+        output
+    );
+}
+
+fn main() {
+    let in_file = "bswap.ll";
+    let out_file = "bswap.s";
+    let out_dir = env::var_os("OUT_DIR").expect("env should have $OUT_DIR");
+    let out_path = Path::new(&out_dir).join(out_file);
+    compile(
+        in_file,
+        out_path.to_str().expect("$OUT_DIR should be UTF-8"),
+    );
+
+    let src_path = Path::new(&out_dir).join("bswap.rs");
+    let src = format!("pub static ASSEMBLY: &str = include_str!(\"{out_file}\");");
+    fs::write(src_path, src).expect("should be able to write in $OUT_DIR");
+
+    println!("cargo:rerun-if-changed=build.rs");
+    println!("cargo:rerun-if-changed=bswap.ll");
+}
diff --git a/crates/extensions/src/lib.rs b/crates/extensions/src/lib.rs
new file mode 100644
index 0000000..171705b
--- /dev/null
+++ b/crates/extensions/src/lib.rs
@@ -0,0 +1,40 @@
+//! Custom RISC-V extension in PolkaVM that are partially supported.
+//! We use inline assembly to emit partially supported instructions.
+
+use inkwell::{context::Context, module::Module, support::LLVMString};
+
+include!(concat!(env!("OUT_DIR"), "/bswap.rs"));
+
+/// Returns a LLVM module containing a `__bswap` function, which
+/// - Takes a `i256` value argument
+/// - Byte swaps it using `rev8` from the `zbb` extension
+/// - Returns the `i256` value
+///
+/// Returns `Error` if the module fails to validate, which should never happen.
+pub fn module<'context>(
+    context: &'context Context,
+    module_name: &str,
+) -> Result<Module<'context>, LLVMString> {
+    let module = context.create_module(module_name);
+
+    module.set_inline_assembly(ASSEMBLY);
+    module.verify()?;
+
+    Ok(module)
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn assembly_contains_rev8_instruction() {
+        assert!(crate::ASSEMBLY.contains("rev8"));
+    }
+
+    #[test]
+    fn module_is_valid() {
+        inkwell::targets::Target::initialize_riscv(&Default::default());
+        let context = inkwell::context::Context::create();
+
+        assert!(crate::module(&context, "polkavm_bswap").is_ok());
+    }
+}
diff --git a/crates/linker/polkavm_guest.bc b/crates/linker/polkavm_guest.bc
deleted file mode 100644
index fa532df..0000000
Binary files a/crates/linker/polkavm_guest.bc and /dev/null differ