diff --git a/androscalpel/src/dex_fragment.rs b/androscalpel/src/dex_fragment.rs
index aaea8db..e369844 100644
--- a/androscalpel/src/dex_fragment.rs
+++ b/androscalpel/src/dex_fragment.rs
@@ -10,6 +10,7 @@ use crate::Result;
 use crate::*;
 use androscalpel_serializer::*;
 
+use crate::dex_writer::DexIndex;
 use crate::ins::{CallSite, Instruction};
 use crate::instructions::*;
 use androscalpel_serializer::Instruction as InsFormat;
@@ -572,12 +573,13 @@ impl DexFragment {
         Ok(())
     }
 
+    // TODO: find if there is a way to efficiently link code item.
     /// Insert a code_item.
     ///
-    /// # Warning
-    ///
-    /// This is currently a stub that probably serialize invalid references to data.
-    fn insert_code_item(&mut self, code: &Code, index: &FragIndex) -> Result<()> {
+    /// This item cannot be cached, because the jump instructions depend on the size of
+    /// instructions that depend on the size of the descriptor ids that depend on the
+    /// list of all descriptors in the dex file.
+    fn insert_code_item(&mut self, code: &Code, index: &DexIndex) -> Result<()> {
         // Estimate instructions addresses
         let mut min_addr = 0;
         let mut max_addr = 0;
@@ -1563,11 +1565,14 @@ impl DexFragment {
             let access_flags =
                 Uleb128(class.direct_methods.get(id).unwrap().get_raw_access_flags());
             let code_off = if let Some(code) = &class.direct_methods.get(id).unwrap().code {
-                let code_off = self.section_manager.get_aligned_size(FragSection::CodeItem);
-                self.insert_code_item(code, index).with_context(|| {
-                    format!("Failed to convert serialize code of {}", id.__str__())
-                })?;
-                Uleb128(code_off + 1)
+                // CodeItems depend to much on the complte descriptor list to be generated
+                // prior to linking
+                //let code_off = self.section_manager.get_aligned_size(FragSection::CodeItem);
+                //self.insert_code_item(code, index).with_context(|| {
+                //    format!("Failed to convert serialize code of {}", id.__str__())
+                //})?;
+                //Uleb128(code_off + 1)
+                Uleb128(1)
             } else {
                 Uleb128(0)
             };
@@ -1597,11 +1602,14 @@ impl DexFragment {
                     .get_raw_access_flags(),
             );
             let code_off = if let Some(code) = &class.virtual_methods.get(id).unwrap().code {
-                let code_off = self.section_manager.get_aligned_size(FragSection::CodeItem);
-                self.insert_code_item(code, index).with_context(|| {
-                    format!("Failed to convert serialize code of {}", id.__str__())
-                })?;
-                Uleb128(code_off + 1)
+                // CodeItems depend to much on the complte descriptor list to be generated
+                // prior to linking
+                // let code_off = self.section_manager.get_aligned_size(FragSection::CodeItem);
+                // self.insert_code_item(code, index).with_context(|| {
+                //    format!("Failed to convert serialize code of {}", id.__str__())
+                // })?;
+                // Uleb128(code_off + 1)
+                Uleb128(1)
             } else {
                 Uleb128(0)
             };
@@ -1884,21 +1892,19 @@ impl DexFragment {
     /// linked before.
     pub fn link_global_ids(
         &mut self,
-        global_strings: &[DexString],
-        global_type_ids: &[IdType],
-        global_proto_ids: &[IdMethodType],
-        global_field_ids: &[IdField],
-        global_method_ids: &[IdMethod],
+        class: &Class,
+        index: &DexIndex,
         nb_method_handle_before_fragment: usize,
     ) -> Result<()> {
         self.link_state.start_linking_idx()?;
         let string_reindex = Vec::with_capacity(self.strings.len());
+        // TODO: considering we have the map, this can be simplified a lot
         let mut global_idx = 0;
         for s in self.strings {
-            while global_idx < global_strings.len() && global_strings[global_idx] != s {
+            while global_idx < index.strings_list.len() && index.strings_list[global_idx] != s {
                 global_idx += 1;
             }
-            if global_idx == global_strings.len() {
+            if global_idx == index.strings_list.len() {
                 bail!("String {} not found in global index", s.__str__());
             }
             string_reindex.push(global_idx as u32);
@@ -1906,10 +1912,10 @@ impl DexFragment {
         let type_reindex = Vec::with_capacity(self.type_ids.len());
         let mut global_idx = 0;
         for ty in self.type_ids {
-            while global_idx < global_type_ids.len() && global_type_ids[global_idx] != ty {
+            while global_idx < index.type_ids_list.len() && index.type_ids_list[global_idx] != ty {
                 global_idx += 1;
             }
-            if global_idx == global_type_ids.len() {
+            if global_idx == index.type_ids_list.len() {
                 bail!("Type {} not found in global index", ty.__str__());
             }
             type_reindex.push(global_idx as u32);
@@ -1917,10 +1923,12 @@ impl DexFragment {
         let proto_reindex = Vec::with_capacity(self.proto_ids.len());
         let mut global_idx = 0;
         for proto in self.proto_ids {
-            while global_idx < global_proto_ids.len() && global_proto_ids[global_idx] != proto {
+            while global_idx < index.proto_ids_list.len()
+                && index.proto_ids_list[global_idx] != proto
+            {
                 global_idx += 1;
             }
-            if global_idx == global_proto_ids.len() {
+            if global_idx == index.proto_ids_list.len() {
                 bail!("Prototype {} not found in global index", proto.__str__());
             }
             proto_reindex.push(global_idx as u32);
@@ -1928,10 +1936,12 @@ impl DexFragment {
         let field_reindex = Vec::with_capacity(self.field_ids.len());
         let mut global_idx = 0;
         for field in self.field_ids {
-            while global_idx < global_field_ids.len() && global_field_ids[global_idx] != field {
+            while global_idx < index.field_ids_list.len()
+                && index.field_ids_list[global_idx] != field
+            {
                 global_idx += 1;
             }
-            if global_idx == global_field_ids.len() {
+            if global_idx == index.field_ids_list.len() {
                 bail!("Field {} not found in global index", field.__str__());
             }
             field_reindex.push(global_idx as u16);
@@ -1939,18 +1949,23 @@ impl DexFragment {
         let method_reindex = Vec::with_capacity(self.method_ids.len());
         let mut global_idx = 0;
         for meth in self.method_ids {
-            while global_idx < global_method_ids.len() && global_method_ids[global_idx] != meth {
+            while global_idx < index.method_ids_list.len()
+                && index.method_ids_list[global_idx] != meth
+            {
                 global_idx += 1;
             }
-            if global_idx == global_method_ids.len() {
+            if global_idx == index.method_ids_list.len() {
                 bail!("Method {} not found in global index", meth.__str__());
             }
             method_reindex.push(global_idx as u16);
         }
 
+        self.link_id_class_data_and_gen_code(class, &field_reindex, &method_reindex, index)?;
         self.link_id_class_def(&string_reindex, &type_reindex);
         self.link_id_method_handle(&field_reindex, &method_reindex);
 
+        // GEN CODE
+
         todo!()
     }
 
@@ -1977,51 +1992,6 @@ impl DexFragment {
         }
     }
 
-    fn link_id_code(&mut self, string_reindex: &[u32], type_reindex: &[u32]) {
-        let mut total_size = 0;
-        let mut code_item_relocation = if let FragLinkState::LinkedIdx {
-            code_item_relocation,
-            ..
-        } = self.link_state
-        {
-            code_item_relocation
-        } else {
-            // link_global_ids() should prevent that
-            panic!("link_id_code should not be run outside of fn link_global_ids(..)");
-        };
-        for code in self.code_items {
-            let current_size = code.size();
-            for ins in &mut code.insns {
-                Self::link_id_ins(ins, string_reindex);
-            }
-            // TODO: TryItem recompute handler_off
-            if let Some(handlers) = code.handlers {
-                let mut handler_off_reindex = HashMap::new();
-                let mut current_offset = handlers.size_field().size();
-                let mut old_offset = handlers.size_field().size();
-                for handlers in handlers.list {
-                    handler_off_reindex.insert(old_offset as u16, current_offset as u16);
-                    old_offset += handlers.size();
-                    for handler in handlers.handlers {
-                        handler.type_idx.0 = type_reindex[handler.type_idx.0 as usize];
-                    }
-                    current_offset += handlers.size();
-                }
-                for try_ in code.tries {
-                    try_.handler_off = *handler_off_reindex
-                        .get(&try_.handler_off)
-                        .expect("Something whent wrong with the handle reindexing");
-                }
-            }
-        }
-    }
-    fn link_id_ins(ins: &mut InsFormat, string_reindex: &[u32]) {
-        match ins {
-            InsFormat::Format31C { op: 0x1b, b, .. } => *b = string_reindex[b as usize],
-            InsFormat::Format21C { op: 0x1a, b, .. } => todo!(), // TODO FUCK this
-            _ => todo!(),
-        }
-    }
     fn link_id_string_data(&mut self) {
         todo!()
     }
@@ -2037,8 +2007,103 @@ impl DexFragment {
     fn link_id_annotation_dir(&mut self) {
         todo!()
     }
-    fn link_id_class_data(&mut self) {
-        todo!()
+
+    /// Link ids in [`ClassDataItem`] *and* generate the [`CodeItem`].
+    fn link_id_class_data_and_gen_code(
+        &mut self,
+        class: &Class,
+        field_reindex: &[u16],
+        method_reindex: &[u16],
+        index: &DexIndex,
+    ) -> Result<()> {
+        if let Some(data) = self.class_data {
+            let mut last_local_id = 0;
+            let mut last_global_id = 0;
+            for field in data.static_fields {
+                let new_local_id = last_local_id + field.field_idx_diff.0;
+                let new_global_id = field_reindex[new_local_id as usize];
+                field.field_idx_diff.0 = (new_global_id - last_global_id) as u32;
+                last_local_id = new_local_id;
+                last_global_id = new_global_id;
+            }
+            let mut last_local_id = 0;
+            let mut last_global_id = 0;
+            for field in data.instance_fields {
+                let new_local_id = last_local_id + field.field_idx_diff.0;
+                let new_global_id = field_reindex[new_local_id as usize];
+                field.field_idx_diff.0 = (new_global_id - last_global_id) as u32;
+                last_local_id = new_local_id;
+                last_global_id = new_global_id;
+            }
+
+            let mut last_local_id = 0;
+            let mut last_global_id = 0;
+            for meth in data.direct_methods {
+                let new_local_id = last_local_id + meth.method_idx_diff.0;
+                let new_global_id = field_reindex[new_local_id as usize];
+                meth.method_idx_diff.0 = (new_global_id - last_global_id) as u32;
+                if meth.code_off.0 != 0 {
+                    let meth_id = index.method_ids_list[new_global_id as usize];
+                    let code = class
+                        .direct_methods
+                        .get(&meth_id)
+                        .ok_or(anyhow!(
+                            "direct method {} expected from fragment but not found in {}",
+                            meth_id.__str__(),
+                            class.__str__()
+                        ))?
+                        .code;
+                    if let Some(code) = code {
+                        let code_off = self.section_manager.get_aligned_size(FragSection::CodeItem);
+                        self.insert_code_item(&code, index)?;
+                        meth.code_off.0 = code_off + 1;
+                    } else {
+                        bail!(
+                            "Inconsistant fragment: fragment expect a code item for {}\
+                            but none was found in {}",
+                            meth_id.__str__(),
+                            class.__str__()
+                        );
+                    }
+                }
+                last_local_id = new_local_id;
+                last_global_id = new_global_id;
+            }
+            let mut last_local_id = 0;
+            let mut last_global_id = 0;
+            for meth in data.virtual_methods {
+                let new_local_id = last_local_id + meth.method_idx_diff.0;
+                let new_global_id = field_reindex[new_local_id as usize];
+                meth.method_idx_diff.0 = (new_global_id - last_global_id) as u32;
+                if meth.code_off.0 != 0 {
+                    let meth_id = index.method_ids_list[new_global_id as usize];
+                    let code = class
+                        .virtual_methods
+                        .get(&meth_id)
+                        .ok_or(anyhow!(
+                            "virtual method {} expected from fragment but not found in {}",
+                            meth_id.__str__(),
+                            class.__str__()
+                        ))?
+                        .code;
+                    if let Some(code) = code {
+                        let code_off = self.section_manager.get_aligned_size(FragSection::CodeItem);
+                        self.insert_code_item(&code, index)?;
+                        meth.code_off.0 = code_off + 1;
+                    } else {
+                        bail!(
+                            "Inconsistant fragment: fragment expect a code item for {}\
+                            but none was found in {}",
+                            meth_id.__str__(),
+                            class.__str__()
+                        );
+                    }
+                }
+                last_local_id = new_local_id;
+                last_global_id = new_global_id;
+            }
+        }
+        Ok(())
     }
 }
 
@@ -2305,7 +2370,7 @@ impl FragSectionManager {
     }
 }
 
-/// Index that associate a type to its local id in a fragment.
+/// Index that associate descriptors to their local id in a fragment.
 #[derive(Debug, Clone)]
 struct FragIndex {
     pub strings: HashMap<DexString, usize>,
diff --git a/androscalpel/src/dex_writer.rs b/androscalpel/src/dex_writer.rs
index 840872c..854bb73 100644
--- a/androscalpel/src/dex_writer.rs
+++ b/androscalpel/src/dex_writer.rs
@@ -1,34 +1,38 @@
 //! The structure that generate a .dex from classes.
-use std::collections::{HashSet, VecDeque};
+use std::collections::{HashMap, HashSet, VecDeque};
 
 use crate::dex_fragment::DexFragment;
-use crate::{DexString, IdField, IdMethod, IdMethodType, IdType};
+use crate::{Class, DexString, IdField, IdMethod, IdMethodType, IdType, Result};
 
 #[derive(Debug, Clone)]
-pub struct DexWriter {
-    fragments: VecDeque<DexFragment>,
+pub struct DexWriter<'a> {
+    classes: VecDeque<&'a Class>,
 }
 
-impl Default for DexWriter {
+impl<'a> Default for DexWriter<'a> {
     fn default() -> Self {
         Self {
-            fragments: VecDeque::new(),
+            classes: VecDeque::new(),
         }
     }
 }
 
-impl DexWriter {
+impl<'a> DexWriter<'a> {
     pub fn new() -> Self {
         Self::default()
     }
 
     pub fn empty(&self) -> bool {
-        self.fragments.is_empty()
+        self.classes.is_empty()
+    }
+
+    pub fn add_class(&mut self, class: &'a Class) {
+        self.classes.push_back(class)
     }
 
     /// Take as many fragments as possible and convert them to a dex file.
-    pub fn generate_next_dex_file(&mut self) -> Vec<u8> {
-        let mut fragments = vec![];
+    pub fn generate_next_dex_file(&mut self) -> Result<Vec<u8>> {
+        let mut fragments_in_file = vec![];
         let mut string_set: HashSet<DexString> = HashSet::new();
         let mut type_set: HashSet<IdType> = HashSet::new();
         let mut proto_set: HashSet<IdMethodType> = HashSet::new();
@@ -37,8 +41,16 @@ impl DexWriter {
         let mut type_list_set: HashSet<Vec<IdType>> = HashSet::new();
         let mut nb_method_handle = 0;
         let mut nb_method_handle_before = vec![];
+        let fragments: VecDeque<(&'a Class, DexFragment)> = self
+            .classes
+            .into_iter()
+            .map(|class| match DexFragment::new(class) {
+                Ok(frag) => Ok((class, frag)),
+                Err(err) => Err(err),
+            })
+            .collect()?;
         loop {
-            let new_fragment = if let Some(new_fragment) = self.fragments.pop_front() {
+            let (class, new_fragment) = if let Some(new_fragment) = fragments.pop_front() {
                 new_fragment
             } else {
                 break;
@@ -52,7 +64,7 @@ impl DexWriter {
                         .count()
                     > u16::MAX as usize
             {
-                self.fragments.push_front(new_fragment);
+                fragments.push_front((class, new_fragment));
                 break;
             }
             if proto_set.len() + new_fragment.proto_ids().len() > u16::MAX as usize
@@ -64,7 +76,7 @@ impl DexWriter {
                         .count()
                     > u16::MAX as usize
             {
-                self.fragments.push_front(new_fragment);
+                fragments.push_front((class, new_fragment));
                 break;
             }
             if field_set.len() + new_fragment.field_ids().len() > u16::MAX as usize
@@ -76,7 +88,7 @@ impl DexWriter {
                         .count()
                     > u16::MAX as usize
             {
-                self.fragments.push_front(new_fragment);
+                fragments.push_front((class, new_fragment));
                 break;
             }
             if method_set.len() + new_fragment.method_ids().len() > u16::MAX as usize
@@ -88,7 +100,7 @@ impl DexWriter {
                         .count()
                     > u16::MAX as usize
             {
-                self.fragments.push_front(new_fragment);
+                fragments.push_front((class, new_fragment));
                 break;
             }
             string_set.extend(new_fragment.strings().iter().cloned());
@@ -99,32 +111,89 @@ impl DexWriter {
             type_list_set.insert(new_fragment.interfaces().to_vec());
             nb_method_handle_before.push(nb_method_handle);
             nb_method_handle += new_fragment.method_handles().len();
-            fragments.push(new_fragment);
+            fragments_in_file.push((class, new_fragment));
         }
         type_list_set.extend(proto_set.iter().map(|proto| proto.parameters.clone()));
-        let mut strings: Vec<DexString> = string_set.into_iter().collect();
+        let mut strings: Vec<DexString> = string_set.iter().cloned().collect();
         strings.sort();
-        let mut type_ids: Vec<IdType> = type_set.into_iter().collect();
+        let mut type_ids: Vec<IdType> = type_set.iter().cloned().collect();
         type_ids.sort();
-        let mut proto_ids: Vec<IdMethodType> = proto_set.into_iter().collect();
+        let mut proto_ids: Vec<IdMethodType> = proto_set.iter().cloned().collect();
         proto_ids.sort();
-        let mut field_ids: Vec<IdField> = field_set.into_iter().collect();
+        let mut field_ids: Vec<IdField> = field_set.iter().cloned().collect();
         field_ids.sort();
-        let mut method_ids: Vec<IdMethod> = method_set.into_iter().collect();
+        let mut method_ids: Vec<IdMethod> = method_set.iter().cloned().collect();
         method_ids.sort();
-        let mut type_lists: Vec<Vec<IdType>> = type_list_set.into_iter().collect();
+        let mut type_lists: Vec<Vec<IdType>> = type_list_set.iter().cloned().collect();
+        let index = DexIndex::new(&strings, &type_ids, &proto_ids, &field_ids, &method_ids);
 
-        for (i, fragment) in fragments.iter().enumerate() {
-            fragment.link_global_ids(
-                &strings,
-                &type_ids,
-                &proto_ids,
-                &field_ids,
-                &method_ids,
-                nb_method_handle_before[i],
-            );
+        for (i, (class, fragment)) in fragments_in_file.iter().enumerate() {
+            fragment.link_global_ids(&index, nb_method_handle_before[i]);
         }
 
-        vec![]
+        Ok(vec![])
+    }
+}
+
+/// Index that associate descriptors to their id in the dex file.
+#[derive(Debug, Clone)]
+pub(crate) struct DexIndex<'a> {
+    pub strings: HashMap<DexString, usize>,
+    pub types: HashMap<IdType, usize>,
+    pub protos: HashMap<IdMethodType, usize>,
+    pub fields: HashMap<IdField, usize>,
+    pub methods: HashMap<IdMethod, usize>,
+    pub strings_list: &'a [DexString],
+    pub type_ids_list: &'a [IdType],
+    pub proto_ids_list: &'a [IdMethodType],
+    pub field_ids_list: &'a [IdField],
+    pub method_ids_list: &'a [IdMethod],
+}
+
+impl<'a> DexIndex<'a> {
+    fn new(
+        strings_list: &'a [DexString],
+        type_ids_list: &'a [IdType],
+        proto_ids_list: &'a [IdMethodType],
+        field_ids_list: &'a [IdField],
+        method_ids_list: &'a [IdMethod],
+    ) -> Self {
+        Self {
+            strings_list,
+            type_ids_list,
+            proto_ids_list,
+            field_ids_list,
+            method_ids_list,
+            strings: strings_list
+                .iter()
+                .cloned()
+                .enumerate()
+                .map(|(x, y)| (y, x))
+                .collect(),
+            types: type_ids_list
+                .iter()
+                .cloned()
+                .enumerate()
+                .map(|(x, y)| (y, x))
+                .collect(),
+            protos: proto_ids_list
+                .iter()
+                .cloned()
+                .enumerate()
+                .map(|(x, y)| (y, x))
+                .collect(),
+            fields: field_ids_list
+                .iter()
+                .cloned()
+                .enumerate()
+                .map(|(x, y)| (y, x))
+                .collect(),
+            methods: method_ids_list
+                .iter()
+                .cloned()
+                .enumerate()
+                .map(|(x, y)| (y, x))
+                .collect(),
+        }
     }
 }