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Use repr(packed) If struct requires explicit alignment of 1. #1075

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merged 2 commits into from
Oct 11, 2017
Merged

Use repr(packed) If struct requires explicit alignment of 1. #1075

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2a57d7c
Refactor requires_explicit_align
pepyakin Oct 11, 2017
746c743
Handle explicit align=1.
pepyakin Oct 11, 2017
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3 changes: 1 addition & 2 deletions bindgen-integration/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -183,8 +183,7 @@ fn test_bitfields_sixth() {
fn test_bitfield_constructors() {
use std::mem;
let mut first = bindings::bitfields::First {
_bitfield_1: unsafe { mem::transmute(bindings::bitfields::First::new_bitfield_1(1, 2, 3)) },
__bindgen_align: [],
_bitfield_1: unsafe { mem::transmute(bindings::bitfields::First::new_bitfield_1(1, 2, 3)) }
};
assert!(unsafe {
first.assert(1, 2, 3)
Expand Down
197 changes: 104 additions & 93 deletions src/codegen/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1380,6 +1380,8 @@ impl CodeGenerator for CompInfo {

let used_template_params = item.used_template_params(ctx);

let mut packed = self.packed();

// generate tuple struct if struct or union is a forward declaration,
// skip for now if template parameters are needed.
//
Expand All @@ -1397,97 +1399,8 @@ impl CodeGenerator for CompInfo {
return;
}

let mut attributes = vec![];
let mut needs_clone_impl = false;
let mut needs_default_impl = false;
let mut needs_debug_impl = false;
let mut needs_partialeq_impl = false;
if let Some(comment) = item.comment(ctx) {
attributes.push(attributes::doc(comment));
}
if self.packed() {
attributes.push(attributes::repr_list(&["C", "packed"]));
} else {
attributes.push(attributes::repr("C"));
}

let is_union = self.kind() == CompKind::Union;
let mut derives = vec![];
if item.can_derive_debug(ctx) {
derives.push("Debug");
} else {
needs_debug_impl = ctx.options().derive_debug &&
ctx.options().impl_debug
}

if item.can_derive_default(ctx) {
derives.push("Default");
} else {
needs_default_impl = ctx.options().derive_default;
}

if item.can_derive_copy(ctx) && !item.annotations().disallow_copy() &&
ctx.options().derive_copy
{
derives.push("Copy");
if used_template_params.is_some() {
// FIXME: This requires extra logic if you have a big array in a
// templated struct. The reason for this is that the magic:
// fn clone(&self) -> Self { *self }
// doesn't work for templates.
//
// It's not hard to fix though.
derives.push("Clone");
} else {
needs_clone_impl = true;
}
}

if item.can_derive_hash(ctx) {
derives.push("Hash");
}

if item.can_derive_partialord(ctx) {
derives.push("PartialOrd");
}

if item.can_derive_ord(ctx) {
derives.push("Ord");
}

if item.can_derive_partialeq(ctx) {
derives.push("PartialEq");
} else {
needs_partialeq_impl =
ctx.options().derive_partialeq &&
ctx.options().impl_partialeq &&
ctx.lookup_can_derive_partialeq_or_partialord(item.id())
.map_or(true, |x| {
x == CannotDeriveReason::ArrayTooLarge
});
}

if item.can_derive_eq(ctx) {
derives.push("Eq");
}

if !derives.is_empty() {
attributes.push(attributes::derives(&derives))
}

let canonical_name = item.canonical_name(ctx);
let canonical_ident = ctx.rust_ident(&canonical_name);
let mut tokens = if is_union && self.can_be_rust_union(ctx) {
quote! {
#( #attributes )*
pub union #canonical_ident
}
} else {
quote! {
#( #attributes )*
pub struct #canonical_ident
}
};

// Generate the vtable from the method list if appropriate.
//
Expand Down Expand Up @@ -1540,6 +1453,8 @@ impl CodeGenerator for CompInfo {
});
}
}

let is_union = self.kind() == CompKind::Union;
if is_union {
result.saw_union();
if !self.can_be_rust_union(ctx) {
Expand Down Expand Up @@ -1612,10 +1527,17 @@ impl CodeGenerator for CompInfo {
fields.push(padding_field);
}

if let Some(align_field) =
layout.and_then(|layout| struct_layout.align_struct(layout))
{
fields.push(align_field);
if let Some(layout) = layout {
if struct_layout.requires_explicit_align(layout) {
if layout.align == 1 {
packed = true;
} else {
let ty = helpers::blob(Layout::new(0, layout.align));
fields.push(quote! {
pub __bindgen_align: #ty ,
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This will only work to increase alignment, right? So what if we are decreasing alignment (but not all the way to 1)? I guess that requires #pragma packed or __attribute__((aligned(..))) which we don't fully support yet.

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Yep. If one would try to decrease alignment it would lead to layout test failure... just as it is now.

});
}
}
}
}

Expand Down Expand Up @@ -1674,6 +1596,95 @@ impl CodeGenerator for CompInfo {
quote! { }
};

let mut attributes = vec![];
let mut needs_clone_impl = false;
let mut needs_default_impl = false;
let mut needs_debug_impl = false;
let mut needs_partialeq_impl = false;
if let Some(comment) = item.comment(ctx) {
attributes.push(attributes::doc(comment));
}
if packed {
attributes.push(attributes::repr_list(&["C", "packed"]));
} else {
attributes.push(attributes::repr("C"));
}

let mut derives = vec![];
if item.can_derive_debug(ctx) {
derives.push("Debug");
} else {
needs_debug_impl = ctx.options().derive_debug &&
ctx.options().impl_debug
}

if item.can_derive_default(ctx) {
derives.push("Default");
} else {
needs_default_impl = ctx.options().derive_default;
}

if item.can_derive_copy(ctx) && !item.annotations().disallow_copy() &&
ctx.options().derive_copy
{
derives.push("Copy");
if used_template_params.is_some() {
// FIXME: This requires extra logic if you have a big array in a
// templated struct. The reason for this is that the magic:
// fn clone(&self) -> Self { *self }
// doesn't work for templates.
//
// It's not hard to fix though.
derives.push("Clone");
} else {
needs_clone_impl = true;
}
}

if item.can_derive_hash(ctx) {
derives.push("Hash");
}

if item.can_derive_partialord(ctx) {
derives.push("PartialOrd");
}

if item.can_derive_ord(ctx) {
derives.push("Ord");
}

if item.can_derive_partialeq(ctx) {
derives.push("PartialEq");
} else {
needs_partialeq_impl =
ctx.options().derive_partialeq &&
ctx.options().impl_partialeq &&
ctx.lookup_can_derive_partialeq_or_partialord(item.id())
.map_or(true, |x| {
x == CannotDeriveReason::ArrayTooLarge
});
}

if item.can_derive_eq(ctx) {
derives.push("Eq");
}

if !derives.is_empty() {
attributes.push(attributes::derives(&derives))
}

let mut tokens = if is_union && self.can_be_rust_union(ctx) {
quote! {
#( #attributes )*
pub union #canonical_ident
}
} else {
quote! {
#( #attributes )*
pub struct #canonical_ident
}
};
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This whole chunk is just code motion right?

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Yes!


tokens.append(quote! {
#generics {
#( #fields )*
Expand Down
13 changes: 2 additions & 11 deletions src/codegen/struct_layout.rs
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Expand Up @@ -288,18 +288,9 @@ impl<'a> StructLayoutTracker<'a> {
}
}

pub fn align_struct(&self, layout: Layout) -> Option<quote::Tokens> {
if self.max_field_align < layout.align &&
pub fn requires_explicit_align(&self, layout: Layout) -> bool {
self.max_field_align < layout.align &&
layout.align <= mem::size_of::<*mut ()>()
{
let ty = helpers::blob(Layout::new(0, layout.align));

Some(quote! {
pub __bindgen_align: #ty ,
})
} else {
None
}
}

fn padding_bytes(&self, layout: Layout) -> usize {
Expand Down
3 changes: 1 addition & 2 deletions tests/expectations/tests/bitfield-32bit-overflow.rs
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Expand Up @@ -4,11 +4,10 @@
#![allow(dead_code, non_snake_case, non_camel_case_types, non_upper_case_globals)]


#[repr(C)]
#[repr(C, packed)]
#[derive(Debug, Default, Copy)]
pub struct MuchBitfield {
pub _bitfield_1: [u8; 5usize],
pub __bindgen_align: [u8; 0usize],
}
#[test]
fn bindgen_test_layout_MuchBitfield() {
Expand Down
3 changes: 1 addition & 2 deletions tests/expectations/tests/bitfield-method-same-name.rs
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Expand Up @@ -4,11 +4,10 @@
#![allow(dead_code, non_snake_case, non_camel_case_types, non_upper_case_globals)]


#[repr(C)]
#[repr(C, packed)]
#[derive(Debug, Default, Copy)]
pub struct Foo {
pub _bitfield_1: u8,
pub __bindgen_align: [u8; 0usize],
}
#[test]
fn bindgen_test_layout_Foo() {
Expand Down
35 changes: 35 additions & 0 deletions tests/expectations/tests/issue-1034.rs
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@@ -0,0 +1,35 @@
/* automatically generated by rust-bindgen */


#![allow(dead_code, non_snake_case, non_camel_case_types, non_upper_case_globals)]


#[repr(C, packed)]
#[derive(Debug, Default, Copy)]
pub struct S2 {
pub _bitfield_1: u16,
}
#[test]
fn bindgen_test_layout_S2() {
assert_eq!(
::std::mem::size_of::<S2>(),
2usize,
concat!("Size of: ", stringify!(S2))
);
assert_eq!(
::std::mem::align_of::<S2>(),
1usize,
concat!("Alignment of ", stringify!(S2))
);
}
impl Clone for S2 {
fn clone(&self) -> Self {
*self
}
}
impl S2 {
#[inline]
pub fn new_bitfield_1() -> u16 {
0
}
}
3 changes: 1 addition & 2 deletions tests/expectations/tests/only_bitfields.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,11 +4,10 @@
#![allow(dead_code, non_snake_case, non_camel_case_types, non_upper_case_globals)]


#[repr(C)]
#[repr(C, packed)]
#[derive(Debug, Default, Copy)]
pub struct C {
pub _bitfield_1: u8,
pub __bindgen_align: [u8; 0usize],
}
#[test]
fn bindgen_test_layout_C() {
Expand Down
4 changes: 4 additions & 0 deletions tests/headers/issue-1034.h
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@@ -0,0 +1,4 @@

struct S2 {
unsigned : 11
};