diff --git a/src/arch/x86_64/test/bin.rs b/src/arch/x86_64/test/bin.rs
index e181297..238065f 100644
--- a/src/arch/x86_64/test/bin.rs
+++ b/src/arch/x86_64/test/bin.rs
@@ -1,6 +1,6 @@
 use crate::{
     arch::x86_64::*,
-    backend::{Instr as BInstr, Program, pe::Import},
+    backend::{Instr as BInstr, Program, pe::LibImport},
 };
 use std::{fs::OpenOptions, io::Write, os::unix::fs::OpenOptionsExt, process::Command};
 
@@ -72,14 +72,18 @@ fn linux() {
 fn windows() {
     let mut program = Program::<X86_64>::default();
     let entry = program.func([BInstr::Asm(Asm {
-        instrs: vec![push(39), pop(rax), Instr::Ret],
+        instrs: vec![
+            push(39),
+            pop(rax),
+            Instr::Ret
+        ],
     })]);
     program.entry = Some(entry);
     let linked = program.compile().expect("failed to compile");
 
-    let imports = &[Import {
+    let imports = &[LibImport {
         name: "KERNEL32.dll".to_string(),
-        names: ["GetStdHandle", "WriteFile", "ExitProcess"]
+        syms: ["GetStdHandle", "WriteFile", "ExitProcess"]
             .map(String::from)
             .to_vec(),
     }];
diff --git a/src/backend/container/pe/import.rs b/src/backend/container/pe/import.rs
index eda26f6..e8487a0 100644
--- a/src/backend/container/pe/import.rs
+++ b/src/backend/container/pe/import.rs
@@ -2,12 +2,17 @@ use crate::backend::pe::data_dir::DataDir;
 
 use super::ByteEncoder;
 
-pub struct Import {
+pub struct LibImport {
     pub name: String,
-    pub names: Vec<String>,
+    pub syms: Vec<SymImport>,
 }
 
-pub fn encode(data: &mut ByteEncoder, imports: &[Import]) -> DataDir {
+pub struct SymImport {
+    name: String,
+    usages: Vec<usize>,
+}
+
+pub fn encode(data: &mut ByteEncoder, imports: &[LibImport]) -> DataDir {
     let start = data.pos() as u32;
     let idt = data.reserve_arr::<ImportDirTable>(imports.len());
     // null entry to mark end
@@ -23,12 +28,12 @@ pub fn encode(data: &mut ByteEncoder, imports: &[Import]) -> DataDir {
         // lookup table
         data.align(size_of::<ImportLookupEntry>());
         let lookup_start = data.pos();
-        let lookup = data.reserve_arr::<ImportLookupEntry>(import.names.len());
+        let lookup = data.reserve_arr::<ImportLookupEntry>(import.syms.len());
         data.pad(size_of::<ImportLookupEntry>());
         let lookup_end = data.pos();
 
-        for (i, name) in import.names.iter().enumerate() {
-            let rva = hint_name_entry(data, 0, name);
+        for (i, sym) in import.syms.iter().enumerate() {
+            let rva = hint_name_entry(data, 0, &sym.name);
             data[lookup][i] = ImportLookupEntry::name(rva);
         }
 
diff --git a/src/backend/container/pe/mod.rs b/src/backend/container/pe/mod.rs
index 6a6de9f..88665c7 100644
--- a/src/backend/container/pe/mod.rs
+++ b/src/backend/container/pe/mod.rs
@@ -7,9 +7,9 @@ use crate::backend::LinkedProgram;
 
 use data_dir::*;
 use header::*;
-pub use import::Import;
+pub use import::LibImport;
 
-pub fn create(program: &[u8], start_offset: u64, imports: &[Import]) -> Vec<u8> {
+pub fn create(program: &[u8], start_offset: u64, imports: &[LibImport]) -> Vec<u8> {
     let mut data = ByteEncoder::default();
     let file_align = 1;
     let section_align = 1;
@@ -105,7 +105,7 @@ pub fn create(program: &[u8], start_offset: u64, imports: &[Import]) -> Vec<u8>
 }
 
 impl LinkedProgram<u64> {
-    pub fn to_pe(&self, imports: &[Import]) -> Vec<u8> {
+    pub fn to_pe(&self, imports: &[LibImport]) -> Vec<u8> {
         create(&self.code, self.entry.expect("no start"), imports)
     }
 }
diff --git a/src/backend/ir/mod.rs b/src/backend/ir/mod.rs
index 7daad48..f18e211 100644
--- a/src/backend/ir/mod.rs
+++ b/src/backend/ir/mod.rs
@@ -9,6 +9,7 @@ pub struct Program<A: Arch> {
     pub ro_data: Vec<Data>,
     pub funcs: Vec<Func<A>>,
     pub entry: Option<Symbol>,
+    pub external: Vec<External>,
 
     sym_count: usize,
 }
@@ -23,6 +24,11 @@ pub struct Func<A: Arch> {
     pub sym: Symbol,
 }
 
+pub struct External {
+    pub file: String,
+    pub syms: Vec<Symbol>,
+}
+
 pub enum Instr<A: Arch> {
     Set { dst: VarId, src: Vec<u8> },
     Call { dst: FnId, args: Vec<VarId> },
@@ -56,6 +62,22 @@ impl<A: Arch> Program<A> {
         sym
     }
 
+    pub fn external<const LEN: usize>(
+        &mut self,
+        file: impl Into<String>,
+        names: [impl Into<String>; LEN],
+    ) -> [Symbol; LEN] {
+        let syms = names.map(|s| {
+            let sym = self.reserve();
+            sym
+        });
+        self.external.push(External {
+            file: file.into(),
+            syms: syms.to_vec(),
+        });
+        syms
+    }
+
     fn reserve(&mut self) -> Symbol {
         let res = Symbol(self.sym_count);
         self.sym_count += 1;
@@ -78,6 +100,7 @@ impl<A: Arch> Default for Program<A> {
             funcs: Default::default(),
             entry: Default::default(),
             sym_count: Default::default(),
+            external: Default::default(),
         }
     }
 }