From: Matt Corallo Date: Sun, 18 Jul 2021 02:09:45 +0000 (+0000) Subject: Provide full (new) struct to trait clone functions X-Git-Tag: v0.0.99.3~4^2~8 X-Git-Url: http://git.bitcoin.ninja/index.cgi?a=commitdiff_plain;h=d7a6aee121ef6089376b0c856e11c4b1d70521b6;p=ldk-c-bindings Provide full (new) struct to trait clone functions Previously, when we went to clone a trait-implementation struct, we'd provide only the `this_arg` void pointer, requiring that the `this_arg` pointer be cloned into a new object while all remaining fields are copied over exactly. This has a few important limitations: * When a struct is cloned, it is not possible to set a `free` function to free any new data placed in `this_arg` without it also being set on the original struct. * Supertrait fields cannot be updated in the subtrait clone method, including the `this_arg` and `free` methods. The first limitation prevents us from setting `free` after a clone when the original trait may or may not have had `free` set. For example, if the original trait was created with a `Obj_as_Trait` method, cloned copies would never be free'd. The second limitation prevents us from keeping the super and subtrait `this_arg` fields in sync, in addition to limitations similar to the above. This resulted in Java code double-free'ing the `this_arg` field in `InMemorySigner` objects which were accessed as both `Sign` and `BaseSign` traits. --- diff --git a/c-bindings-gen/src/main.rs b/c-bindings-gen/src/main.rs index b08f234..4c14074 100644 --- a/c-bindings-gen/src/main.rs +++ b/c-bindings-gen/src/main.rs @@ -237,7 +237,7 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty writeln!(w, "\t/// An opaque pointer which is passed to your function implementations as an argument.").unwrap(); writeln!(w, "\t/// This has no meaning in the LDK, and can be NULL or any other value.").unwrap(); writeln!(w, "\tpub this_arg: *mut c_void,").unwrap(); - let mut generated_fields = Vec::new(); // Every field's (name, is_clonable) except this_arg, used in Clone generation + let mut generated_fields = Vec::new(); // Every field's (name, Option) except this_arg, used in Clone generation for item in t.items.iter() { match item { &syn::TraitItem::Method(ref m) => { @@ -271,14 +271,14 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty // happen) as well as provide an Option<>al function pointer which is // called when the trait method is called which allows updating on the fly. write!(w, "\tpub {}: ", m.sig.ident).unwrap(); - generated_fields.push((format!("{}", m.sig.ident), true)); + generated_fields.push((format!("{}", m.sig.ident), None)); types.write_c_type(w, &*r.elem, Some(&meth_gen_types), false); writeln!(w, ",").unwrap(); writeln!(w, "\t/// Fill in the {} field as a reference to it will be given to Rust after this returns", m.sig.ident).unwrap(); writeln!(w, "\t/// Note that this takes a pointer to this object, not the this_ptr like other methods do").unwrap(); writeln!(w, "\t/// This function pointer may be NULL if {} is filled in when this object is created and never needs updating.", m.sig.ident).unwrap(); writeln!(w, "\tpub set_{}: Option,", m.sig.ident, trait_name).unwrap(); - generated_fields.push((format!("set_{}", m.sig.ident), true)); + generated_fields.push((format!("set_{}", m.sig.ident), None)); // Note that cbindgen will now generate // typedef struct Thing {..., set_thing: (const struct Thing*), ...} Thing; // which does not compile since Thing is not defined before it is used. @@ -291,7 +291,7 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty } write!(w, "\tpub {}: extern \"C\" fn (", m.sig.ident).unwrap(); - generated_fields.push((format!("{}", m.sig.ident), true)); + generated_fields.push((format!("{}", m.sig.ident), None)); write_method_params(w, &m.sig, "c_void", types, Some(&meth_gen_types), true, false); writeln!(w, ",").unwrap(); }, @@ -300,29 +300,24 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty } } // Add functions which may be required for supertrait implementations. - let mut requires_clone = false; - walk_supertraits!(t, Some(&types), ( - ("Clone", _) => requires_clone = true, - (_, _) => {} - ) ); walk_supertraits!(t, Some(&types), ( ("Clone", _) => { - writeln!(w, "\t/// Creates a copy of the object pointed to by this_arg, for a copy of this {}.", trait_name).unwrap(); - writeln!(w, "\t/// Note that the ultimate copy of the {} will have all function pointers the same as the original.", trait_name).unwrap(); - writeln!(w, "\t/// May be NULL if no action needs to be taken, the this_arg pointer will be copied into the new {}.", trait_name).unwrap(); - writeln!(w, "\tpub clone: Option *mut c_void>,").unwrap(); - generated_fields.push(("clone".to_owned(), true)); + writeln!(w, "\t/// Called, if set, after this {} has been cloned into a duplicate object.", trait_name).unwrap(); + writeln!(w, "\t/// The new {} is provided, and should be mutated as needed to perform a", trait_name).unwrap(); + writeln!(w, "\t/// deep copy of the object pointed to by this_arg or avoid any double-freeing.").unwrap(); + writeln!(w, "\tpub cloned: Option,", trait_name, trait_name).unwrap(); + generated_fields.push(("cloned".to_owned(), None)); }, ("std::cmp::Eq", _)|("core::cmp::Eq", _) => { writeln!(w, "\t/// Checks if two objects are equal given this object's this_arg pointer and another object.").unwrap(); writeln!(w, "\tpub eq: extern \"C\" fn (this_arg: *const c_void, other_arg: &{}) -> bool,", trait_name).unwrap(); - generated_fields.push(("eq".to_owned(), true)); + generated_fields.push(("eq".to_owned(), None)); }, ("std::hash::Hash", _)|("core::hash::Hash", _) => { writeln!(w, "\t/// Calculate a succinct non-cryptographic hash for an object given its this_arg pointer.").unwrap(); writeln!(w, "\t/// This is used, for example, for inclusion of this object in a hash map.").unwrap(); writeln!(w, "\tpub hash: extern \"C\" fn (this_arg: *const c_void) -> u64,").unwrap(); - generated_fields.push(("hash".to_owned(), true)); + generated_fields.push(("hash".to_owned(), None)); }, ("Send", _) => {}, ("Sync", _) => {}, (s, i) => { @@ -330,25 +325,22 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty let (docs, name, ret) = convert_trait_impl_field(s); writeln!(w, "\t/// {}", docs).unwrap(); writeln!(w, "\tpub {}: extern \"C\" fn (this_arg: *const c_void) -> {},", name, ret).unwrap(); - (name, true) // Assume clonable + (name, None) // Assume clonable } else { // For in-crate supertraits, just store a C-mapped copy of the supertrait as a member. writeln!(w, "\t/// Implementation of {} for this object.", i).unwrap(); - writeln!(w, "\tpub {}: crate::{},", i, s).unwrap(); let is_clonable = types.is_clonable(s); - if !is_clonable && requires_clone { - writeln!(w, "\t/// Creates a copy of the {}, for a copy of this {}.", i, trait_name).unwrap(); - writeln!(w, "\t/// Because {} doesn't natively support copying itself, you have to provide a full copy implementation here.", i).unwrap(); - writeln!(w, "\tpub {}_clone: extern \"C\" fn (orig_{}: &{}) -> {},", i, i, i, i).unwrap(); - } - (format!("{}", i), is_clonable) + writeln!(w, "\tpub {}: crate::{},", i, s).unwrap(); + (format!("{}", i), if !is_clonable { + Some(format!("crate::{}_clone_fields", s)) + } else { None }) }); } ) ); writeln!(w, "\t/// Frees any resources associated with this object given its this_arg pointer.").unwrap(); writeln!(w, "\t/// Does not need to free the outer struct containing function pointers and may be NULL is no resources need to be freed.").unwrap(); writeln!(w, "\tpub free: Option,").unwrap(); - generated_fields.push(("free".to_owned(), true)); + generated_fields.push(("free".to_owned(), None)); writeln!(w, "}}").unwrap(); macro_rules! impl_trait_for_c { @@ -453,6 +445,20 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty writeln!(w, "unsafe impl Send for {} {{}}", trait_name).unwrap(); writeln!(w, "unsafe impl Sync for {} {{}}", trait_name).unwrap(); + writeln!(w, "#[no_mangle]").unwrap(); + writeln!(w, "pub(crate) extern \"C\" fn {}_clone_fields(orig: &{}) -> {} {{", trait_name, trait_name, trait_name).unwrap(); + writeln!(w, "\t{} {{", trait_name).unwrap(); + writeln!(w, "\t\tthis_arg: orig.this_arg,").unwrap(); + for (field, clone_fn) in generated_fields.iter() { + if let Some(f) = clone_fn { + // If the field isn't clonable, blindly assume its a trait and hope for the best. + writeln!(w, "\t\t{}: {}(&orig.{}),", field, f, field).unwrap(); + } else { + writeln!(w, "\t\t{}: Clone::clone(&orig.{}),", field, field).unwrap(); + } + } + writeln!(w, "\t}}\n}}").unwrap(); + // Implement supertraits for the C-mapped struct. walk_supertraits!(t, Some(&types), ( ("std::cmp::Eq", _)|("core::cmp::Eq", _) => { @@ -469,17 +475,9 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty writeln!(w, "#[no_mangle]").unwrap(); writeln!(w, "/// Creates a copy of a {}", trait_name).unwrap(); writeln!(w, "pub extern \"C\" fn {}_clone(orig: &{}) -> {} {{", trait_name, trait_name, trait_name).unwrap(); - writeln!(w, "\t{} {{", trait_name).unwrap(); - writeln!(w, "\t\tthis_arg: if let Some(f) = orig.clone {{ (f)(orig.this_arg) }} else {{ orig.this_arg }},").unwrap(); - for (field, clonable) in generated_fields.iter() { - if *clonable { - writeln!(w, "\t\t{}: Clone::clone(&orig.{}),", field, field).unwrap(); - } else { - writeln!(w, "\t\t{}: (orig.{}_clone)(&orig.{}),", field, field, field).unwrap(); - writeln!(w, "\t\t{}_clone: orig.{}_clone,", field, field).unwrap(); - } - } - writeln!(w, "\t}}\n}}").unwrap(); + writeln!(w, "\tlet mut res = {}_clone_fields(orig);", trait_name).unwrap(); + writeln!(w, "\tif let Some(f) = orig.cloned {{ (f)(&mut res) }};").unwrap(); + writeln!(w, "\tres\n}}").unwrap(); writeln!(w, "impl Clone for {} {{", trait_name).unwrap(); writeln!(w, "\tfn clone(&self) -> Self {{").unwrap(); writeln!(w, "\t\t{}_clone(self)", trait_name).unwrap(); @@ -805,13 +803,10 @@ fn writeln_impl(w: &mut W, i: &syn::ItemImpl, types: &mut Typ } } let mut requires_clone = false; - walk_supertraits!(trait_obj, Some(&types), ( - ("Clone", _) => requires_clone = true, - (_, _) => {} - ) ); walk_supertraits!(trait_obj, Some(&types), ( ("Clone", _) => { - writeln!(w, "\t\tclone: Some({}_clone_void),", ident).unwrap(); + requires_clone = true; + writeln!(w, "\t\tcloned: Some({}_{}_cloned),", trait_obj.ident, ident).unwrap(); }, ("Sync", _) => {}, ("Send", _) => {}, ("std::marker::Sync", _) => {}, ("std::marker::Send", _) => {}, @@ -829,9 +824,6 @@ fn writeln_impl(w: &mut W, i: &syn::ItemImpl, types: &mut Typ } } write!(w, "\t\t}},\n").unwrap(); - if !types.is_clonable(s) && requires_clone { - writeln!(w, "\t\t{}_clone: {}_{}_clone,", t, ident, t).unwrap(); - } } else { write_trait_impl_field_assign(w, s, ident); } @@ -916,27 +908,21 @@ fn writeln_impl(w: &mut W, i: &syn::ItemImpl, types: &mut Typ _ => unimplemented!(), } } - walk_supertraits!(trait_obj, Some(&types), ( - (s, t) => { - if let Some(supertrait_obj) = types.crate_types.traits.get(s) { - if !types.is_clonable(s) && requires_clone { - writeln!(w, "extern \"C\" fn {}_{}_clone(orig: &crate::{}) -> crate::{} {{", ident, t, s, s).unwrap(); - writeln!(w, "\tcrate::{} {{", s).unwrap(); - writeln!(w, "\t\tthis_arg: orig.this_arg,").unwrap(); - writeln!(w, "\t\tfree: None,").unwrap(); - for item in supertrait_obj.items.iter() { - match item { - syn::TraitItem::Method(m) => { - write_meth!(m, supertrait_obj, ""); - }, - _ => {}, - } - } - write!(w, "\t}}\n}}\n").unwrap(); + if requires_clone { + writeln!(w, "extern \"C\" fn {}_{}_cloned(new_obj: &mut crate::{}) {{", trait_obj.ident, ident, full_trait_path).unwrap(); + writeln!(w, "\tnew_obj.this_arg = {}_clone_void(new_obj.this_arg);", ident).unwrap(); + writeln!(w, "\tnew_obj.free = Some({}_free_void);", ident).unwrap(); + walk_supertraits!(trait_obj, Some(&types), ( + (s, t) => { + if types.crate_types.traits.get(s).is_some() { + assert!(!types.is_clonable(s)); // We don't currently support cloning with a clonable supertrait + writeln!(w, "\tnew_obj.{}.this_arg = new_obj.this_arg;", t).unwrap(); + writeln!(w, "\tnew_obj.{}.free = None;", t).unwrap(); } } - } - ) ); + ) ); + writeln!(w, "}}").unwrap(); + } write!(w, "\n").unwrap(); } else if path_matches_nongeneric(&trait_path.1, &["From"]) { } else if path_matches_nongeneric(&trait_path.1, &["Default"]) {