- Add a ReorderCustomSectionMutator (#954)

- Move AddCustomSectionMutator to custom.rs
- Add CustomSectionMutator to lib.rs so it starts getting used

Co-authored-by: Nick Fitzgerald <[email protected]>

Author: itsrainy

crates/wasm-mutate/src/info.rs

@@ -309,6 +309,31 @@ impl<'a> ModuleInfo<'a> {
         module
     }
 
+    /// Move a section from index `src_idx` to `dest_idx` in the Wasm module
+    pub fn move_section(&self, src_idx: usize, dest_idx: usize) -> wasm_encoder::Module {
+        log::trace!(
+            "moving section from index {} to index {}",
+            src_idx,
+            dest_idx
+        );
+        assert!(src_idx < self.raw_sections.len());
+        assert!(dest_idx < self.raw_sections.len());
+        assert_ne!(src_idx, dest_idx);
+        let mut module = wasm_encoder::Module::new();
+        self.raw_sections.iter().enumerate().for_each(|(i, s)| {
+            if src_idx < dest_idx && i == dest_idx {
+                module.section(&self.raw_sections[src_idx]);
+            }
+            if i != src_idx {
+                module.section(s);
+            }
+            if dest_idx < src_idx && i == dest_idx {
+                module.section(&self.raw_sections[src_idx]);
+            }
+        });
+        module
+    }
+
     /// Replace the `i`th section in this module with the given new section.
     pub fn replace_section(
         &self,

crates/wasm-mutate/src/lib.rs

@@ -17,12 +17,13 @@ mod mutators;
 pub use error::*;
 
 use crate::mutators::{
-    add_custom::AddCustomSectionMutator, add_function::AddFunctionMutator,
-    add_type::AddTypeMutator, codemotion::CodemotionMutator,
-    function_body_unreachable::FunctionBodyUnreachable, modify_const_exprs::ConstExpressionMutator,
-    modify_data::ModifyDataMutator, peephole::PeepholeMutator, remove_export::RemoveExportMutator,
-    remove_item::RemoveItemMutator, remove_section::RemoveSection,
-    rename_export::RenameExportMutator, snip_function::SnipMutator, Item,
+    add_function::AddFunctionMutator, add_type::AddTypeMutator, codemotion::CodemotionMutator,
+    custom::AddCustomSectionMutator, custom::CustomSectionMutator,
+    custom::ReorderCustomSectionMutator, function_body_unreachable::FunctionBodyUnreachable,
+    modify_const_exprs::ConstExpressionMutator, modify_data::ModifyDataMutator,
+    peephole::PeepholeMutator, remove_export::RemoveExportMutator, remove_item::RemoveItemMutator,
+    remove_section::RemoveSection, rename_export::RenameExportMutator, snip_function::SnipMutator,
+    Item,
 };
 use info::ModuleInfo;
 use mutators::Mutator;
@@ -213,6 +214,8 @@ impl<'wasm> WasmMutate<'wasm> {
             &CodemotionMutator,
             &FunctionBodyUnreachable,
             &AddCustomSectionMutator,
+            &ReorderCustomSectionMutator,
+            &CustomSectionMutator,
             &AddTypeMutator {
                 max_params: 20,
                 max_results: 20,

crates/wasm-mutate/src/mutators.rs

@@ -20,7 +20,6 @@
 //! functions is processed in order to construct an equivalent piece of code.
 //!
 
-pub mod add_custom;
 pub mod add_function;
 pub mod add_type;
 pub mod codemotion;

crates/wasm-mutate/src/mutators/add_custom.rs

@@ -72,10 +72,97 @@ impl Mutator for CustomSectionMutator {
     }
 }
 
+#[derive(Clone, Copy)]
+pub struct AddCustomSectionMutator;
+
+const MAX_NEW_DATA_LEN: usize = 100;
+const MAX_NEW_NAME_LEN: usize = 20;
+
+impl Mutator for AddCustomSectionMutator {
+    fn can_mutate(&self, config: &crate::WasmMutate) -> bool {
+        !config.reduce
+    }
+
+    fn mutate<'a>(
+        &self,
+        config: &'a mut crate::WasmMutate,
+    ) -> crate::Result<Box<dyn Iterator<Item = crate::Result<wasm_encoder::Module>> + 'a>> {
+        let num_sections = config.info().raw_sections.len();
+        let new_custom_section_idx = config.rng().gen_range(0..=num_sections);
+        let mut name = vec![];
+        config.raw_mutate(&mut name, MAX_NEW_NAME_LEN)?;
+        let name = String::from_utf8_lossy(&name);
+        let mut data = vec![];
+        config.raw_mutate(&mut data, MAX_NEW_DATA_LEN)?;
+
+        Ok(Box::new(std::iter::once(Ok(config.info().insert_section(
+            new_custom_section_idx,
+            &wasm_encoder::CustomSection {
+                name: &name,
+                data: &data,
+            },
+        )))))
+    }
+}
+
+#[derive(Copy, Clone)]
+pub struct ReorderCustomSectionMutator;
+
+impl Mutator for ReorderCustomSectionMutator {
+    fn can_mutate(&self, config: &crate::WasmMutate) -> bool {
+        config.info().has_custom_section() && config.info().raw_sections.len() > 1
+    }
+
+    fn mutate<'a>(
+        &self,
+        config: &'a mut crate::WasmMutate,
+    ) -> crate::Result<Box<dyn Iterator<Item = crate::Result<wasm_encoder::Module>> + 'a>> {
+        let custom_section_indices: Vec<_> = config
+            .info()
+            .raw_sections
+            .iter()
+            .enumerate()
+            .filter(|(_i, s)| s.id == wasm_encoder::SectionId::Custom as u8)
+            .map(|(i, _s)| i)
+            .collect();
+        assert!(!custom_section_indices.is_empty());
+
+        let src_idx = *custom_section_indices.choose(config.rng()).unwrap();
+        let num_sections = config.info().raw_sections.len();
+        let mut dest_idx;
+        loop {
+            dest_idx = config.rng().gen_range(0..num_sections);
+            if dest_idx != src_idx {
+                break;
+            }
+            config.consume_fuel(1)?;
+        }
+
+        Ok(Box::new(std::iter::once(Ok(config
+            .info()
+            .move_section(src_idx, dest_idx)))))
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
 
+    #[test]
+    fn test_add_custom_section() {
+        crate::mutators::match_mutation(
+            r#"
+                (module)
+            "#,
+            AddCustomSectionMutator,
+            r#"
+                (module
+                    (@custom "a" "b")
+                )
+            "#,
+        );
+    }
+
     #[test]
     fn test_grow_custom_section() {
         crate::mutators::match_mutation(
@@ -143,4 +230,23 @@ mod tests {
             "#,
         );
     }
+
+    #[test]
+    fn test_reorder_custom_section() {
+        crate::mutators::match_mutation(
+            r#"
+            (module
+                (@custom "name" "data")
+                (@custom "name2" "data")
+            )
+            "#,
+            ReorderCustomSectionMutator,
+            r#"
+            (module
+                (@custom "name2" "data")
+                (@custom "name" "data")
+            )
+            "#,
+        )
+    }
 }