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feature request: allow packed types #1704

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bnoordhuis opened this issue Jan 30, 2012 · 3 comments
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feature request: allow packed types #1704

bnoordhuis opened this issue Jan 30, 2012 · 3 comments
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A-type-system Area: Type system C-enhancement Category: An issue proposing an enhancement or a PR with one.

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@bnoordhuis
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Would it be possible to add support for packed types? Types appear to be unpacked right now (which is fine in itself) but it blocks interop with C APIs like epoll_wait.

Example: on x86_64, (0u32, 0u64) is 12 bytes when packed and 16 bytes when unpacked.
@brson
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brson commented Jan 30, 2012

While I do think we should support this in the language, you could probably hack around the problem with unsafe pointers.

bnoordhuis added a commit to bnoordhuis/rust-epoll that referenced this issue Feb 6, 2012
@bnoordhuis
Add failing test.
3d6ab4d 
The kernel expects a packed (no holes) epoll_event struct but Rust doesn't
support packed types yet.

Depends on rust-lang/rust#1704.
@graydon
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graydon commented Feb 15, 2012

I'm ok taking a patch to add packed as a prefix type operator to a record, vector or tuple type. It'll be a bit of a pain to support but does seem to be part of the world we live in.

@graydon graydon mentioned this issue Feb 15, 2012
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@graydon graydon mentioned this issue Mar 14, 2013
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@huonw huonw mentioned this issue Apr 6, 2013
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huonw added a commit to huonw/rust that referenced this issue Apr 9, 2013
@huonw
librustc: implement a #[packed] attribute for structs.
b5ceba1 
A struct (inc. tuple struct) can be annotated with #[packed], so that there
is no padding between its elements, like GCC's `__attribute__((packed))`.

Closes rust-lang#1704.
@huonw huonw mentioned this issue Apr 10, 2013
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huonw added a commit to huonw/rust that referenced this issue Apr 10, 2013
@huonw
librustc: implement a #[packed] attribute for structs.
cad2260 
A struct (inc. tuple struct) can be annotated with #[packed], so that there
is no padding between its elements, like GCC's `__attribute__((packed))`.

Closes rust-lang#1704
bors added a commit that referenced this issue Apr 10, 2013
@bors
auto merge of #5816 : dbaupp/rust/rustc-packed-v2, r=nikomatsakis
5d01f64 
#5758 take 2.

This adds a `#[packed]` attribute for structs, like GCC's `__attribute__((packed))`, e.g.

```rust
#[packed]
struct Size5 {
   a: u8,
   b: u32
}
```

It works on normal and tuple structs, but is (silently) ignored on enums.

Closes #1704.
@thestinger
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Fixed by cad2260

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@graydon @brson @bnoordhuis @thestinger